DFT and TDDFT study of some bifunctional hemithioindigo chromophores

DFT and TDDFT study of some bifunctional hemithioindigo chromophores

Accepted Manuscript Research paper DFT and TDDFT study of some bifunctional hemithioindigo chromophores Samaneh Bagheri Novir PII: DOI: Reference: S0...

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Accepted Manuscript Research paper DFT and TDDFT study of some bifunctional hemithioindigo chromophores Samaneh Bagheri Novir PII: DOI: Reference:

S0009-2614(17)30976-4 https://doi.org/10.1016/j.cplett.2017.10.043 CPLETT 35192

To appear in:

Chemical Physics Letters

Received Date: Accepted Date:

2 September 2017 22 October 2017

Please cite this article as: S. Bagheri Novir, DFT and TDDFT study of some bifunctional hemithioindigo chromophores, Chemical Physics Letters (2017), doi: https://doi.org/10.1016/j.cplett.2017.10.043

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DFT and TDDFT study of some bifunctional hemithioindigo chromophores

Samaneh Bagheri Novir a,* a

Department of Pharmaceutical Chemistry, Faculty of Pharmaceutical Chemistry, Pharmaceutical Sciences Branch, Islamic Azad University, Tehran, Iran

*Corresponding author: S. Bagheri Novir; E-mail: [email protected], [email protected], Tel: +98-9123548308, Fax: +98-21-22600099

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Abstract Quantum chemical study of some of the bifunctional hemithioindigo chromophores has been performed with the aim to determine their cis (Z) and trans (E) properties and to specify the changes of their quantum parameters as a result of the Z/E isomerization. Electronic, photochromic, spectroscopic and other

molecular

properties of these compounds, have been considered by DFT and TDDFT methods. The results of this study show that Cpd. 3c is relatively the most efficient chromophore among the other studied chromophores in this work.

Keywords: Hemithioindigo ; Chromophore; DFT; TDDFT; Absorption spectra

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1. Introduction Photochromic molecules with reversible structural changes from one state into the other through light radiation, have been applied in different fields specially biological applications [1-5]. Generally, Photochromic compounds have been employed in several biological functions such as ion transport [4-7], biocatalysis [5,8,9], cell adhesion [5,10] and protein folding [4,5,11,12]. The structure of bio-molecules such as nucleotides, proteins, peptides and lipids containing reversible photoswitchable chromophores can be changed using light radiation which causes the change of the biological activity of these compounds by light-triggering [5,13]. Most previous studies have been focused on chemical variation of bio-molecules containing azobenzene chromophore as a common reversible photoswitch [4-11]. Numerous types of bio-molecules based on azobenzenebased amino acids such as APB, AMPB, AMPP [13-18] have been employed for particular biological systems. Azobenzene molecule can induce significant geometrical variations of these bio-molecules by isomerization around N=N double bond in reaction to light radiation, while dithienylethenes or spiropyranes chromophores induce the significant changes of electronic properties as s result of the photoswitching of these molecules [1,14,19,20]. Although, the use of azobenzene chromophore in the living organisms or in vivo/vitro investigations may be limited, because the stability of azobenzene chromopeptides strongly depend on their chemical environments. So, novel chromophores with suitable optical properties have been applied for appropriate biological designs [13,14]. Hemithioindigos (HTIs) chromophores have been known as an interesting class of chromophores because of their thermal stability, their frequent reversibility of the isomerizations and their very interesting physical and photophysical properties [1,4,5,21].

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Hemithioindigos are asymmetrical molecules consisting of a thioindigo part connected to a stilbene part via a central C=C bond which this double bond induces that HTIs can be switched under light radiation between the metastable E-isomer (trans) and the thermodynamically most stable Z-isomer (cis). Photoisomerization in both Z to E and E to Z configurations of HTIs can be happened via visible light which is more favorable compared to the application of UV light for azobenzenes isomerization, which this property is the most interesting property of HTIs [1,2,22-24]. Some of bifunctional hemithioindigo chromophores such as ω-amino acid derivatives and dicarboxylic acid esters for connection to proteins and peptides, have been explored [4]. These chromophores can switch around the central C=C bond upon UV-Vis radiation. They are useful for the light alternation of protein structure and related biological systems with large spatial and temporal regulation [13,14,23,25]. The structures of some of the synthesized hemithioindigo-based dicarboxylic acid esters (compounds 3a-3c in Ref. 4) and hemithioindigo-based ω-amino acid derivatives (compounds 9 and 10 in Ref. 4) have been shown in Fig. 1. In compounds 3a-3c, the CO2CH3 group is constantly linked to the thioindigo-part and different substituent groups are linked to the stilbene-part in the para position. In hemithioindigo-based ωamino acid derivatives (Cpds. 9 and 10), the COOH group is constantly attached to the thioindigo-part and the groups in the para position of the stilbene-part of the molecules have been changed. When these HTI-derivatives have been used as a switchable trigger for different protein and peptide structures, significant changes have been observed via isomerization of these compounds [4]. These photochromic hemithioindigo-based dicarboxylic acid esters and ω-amino acid derivatives have not been investigated by quantum computational methods until now. Therefore, quantum chemical calculations have been carried out on both Z- and E-

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isomers of these molecules to study the effects of different substitution groups of both Z- and E-isomers of these compounds and to compare some of the calculated quantum parameters of these molecules in order to explanation and correlation between the experimental biological properties of Z- and E-isomers of the HTI-derivatives and their quantum parameters. The geometrical structure, electronic and nonlinear optical properties, electronic absorption spectra, MEP analysis, thermodynamic properties and other molecular properties of Z- and E-isomers of these photochromic hemithioindigobased dicarboxylic acid esters and ω-amino acid derivatives on the basis of density functional theory (DFT) and time-dependent DFT (TDDFT) methods, are the important purpose of this study.

2. Computational methods In this study, quantum chemical calculations on Z- and E-isomers of some of the photochromic hemithioindigo-derivatives have been carried out by DFT and TDDFT methods in order to study the effects of different substituents on the electronic, optical and spectroscopic properties of these compounds. All calculations in this study, have been carried out with Gaussian 03 package [26]. All the ground states geometries have been optimized by DFT [27] with the B3LYP functional [28-30] and 6-311+G** basis set in methanol solvent by the conductor polarizable continuum model (CPCM) [31-33]. Frequency calculations of the optimized structures have been carried out at the same level to confirm that the optimized structures reach a stationary point and to compute polarizability, hyperpolarizability and thermodynamic quantities of these compounds. Also, the natural population analysis (NPA) and molecular electrostatic potential (MEP) of these molecules have been analyzed at the same level. Excitation energies, maximum absorbances (λmax), oscillator strengths (f) and absorption spectra of all these 5

chromophores have been obtained via the linear response time-dependent DFT (LRTDDFT) method at B3LYP/6-311+G** level for the lowest 30 singlet–singlet transitions of all these compounds . The excitation energies and oscillator strengths have been obtained by calculation of the Casida equations [34-37]. The extinction quantity has been obtained for evaluation of computational and experimental results, from the calculated oscillator strengths with Gaussian functions with an appropriate full width at half maximum, Δ1/2 as [38,39]:

 ( )  2.174  10 8  I

 fI ( 2   2 ) 2  exp 2.773 I 2  1 / 2 1 / 2  

(1)

In this equation, ωI and fI are the excitation frequencies and the oscillator strengths, respectively. Also, the solvent effects in the excited-state calculations have been investigated by the CPCM model. The GaussView molecular visualization program [40] has been used to analyze and presentations of the results of this study.

3. Results and discussion 3.1. Optimized ground-state structure The B3LYP/6-311+G** optimized ground state structures of both Z- and E-isomers of the bifunctional hemithioindigo chromophores in methanol solvent are shown in Fig. 2 and key bond lengths, bond angles and dihedral angles are listed in Table 1. The S7-C8C13-C14 dihedral angles of Z- and E-isomers of all the molecules are virtually

and

, respectively, while their C9-C8-C13-C14 dihedral angles are practically and

, respectively, that show that both Z and E ground state structures of the

molecules are almost planar. Because of steric repulsion, the C8-C13-C14 bond angles 6

value for sp2-

of all the molecules are enlarged slightly rom the predictable hybridi ed carbon atom to to

-

that this bond angle for the Z-isomers were from

, while the ran e or the -isomers

ere rom

to

. Also, the

S7-C8-C13 bond angles of the Z-isomers of all the molecules are in the range between 128. to 128. , while this range for the E-isomers are between 116. to 116. . It is clear that the S7-C8-C13 bond angles of the Z-isomers of all the molecules are larger than those of the E-isomers, while the C8-C13-C14 bond angles of the Z-isomers of all the molecules are somewhat smaller than those of the E-isomers. For all of the studied molecules, the S7-C8, C8-C13 and C13-C14 bond lengths of the E-isomer is somewhat longer than those of the Z-isomer. Among these molecules, Cpd. 3b shows the shortest S7-C8 and C8-C13 bond lengths and the longest C13-C14 bond lengths for both Z- and E-isomers of the molecule. The S7-C8 bond lengths are almost similar ranging from 1.776 to 1.781

or the -isomers and 1.799 to 1.803

or the

isomers. Similarly, The C8-C13 bond lengths are almost similar ranging from 1.352 to 1.355

or the -isomers and 1.359 to 1.364

or the -isomers, and also the C13-

C14 bond lengths are virtually similar ranging from 1.447 to 1.453 and 1.449 to 1.458

or the

or the -isomers

-isomers of the molecules. Therefore, different

substituents appear to decrease the S7-C8 and C8-C13 bond lengths and increase the C13-C14 bond length of Cpd. 3b with the CO2Me in the para-position of the stilbenepart and the COOMe in the thioindigo-part of the molecule, compared to the other molecules. On the basis of the above data, we can conclude that all the bond lengths and bond angles were not significantly altered by isomeric effects except dihedral angles of the molecules which were changed by Z/E isomerization around the C=C double bond of all the molecules.

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3.2. Energetic properties The calculated the highest occupied MO (EHOMO) and the lowest unoccupied MO (ELUMO) values, HLG (ELUMO − EHOMO), total energies and the difference between the energy of the Z structures and the energy of the E structures (relative energies (EZ-EE)) calculated with B3LYP/6-311+G** method in the solvent phase, for optimized structures of both Z- and E-isomers of the bifunctional hemithioindigo chromophores, are listed in Table 2. The values of the relative energies display that the Z-isomers of all the molecules are somewhat more stable than their E-isomers. The ground state energy differences between the Z- and E-isomers of all these molecules were found to be very similar ranging from 0.183 eV for Cpd. 3a to 0.197 eV for the other compounds. It shows that the relative energies were not significantly changed by changing of the R1 groups in the stilbene-part of the compounds, while the relative energies by changing of the R2 group in the thioindigo-part of the compounds were slightly changed. It is clear that, the values of total energies of both Z- and E-isomers of each molecule are very close to each other and have not been considerably changed by Z/E isomerization and by changing of the R1 group in the para-positions of the stilbene-part. However, both isomers of Cpd. 3c with R1=OCH2CO2tBu group and R2=COOMe group shows the lowest total energy levels compared to the other molecules. On the basis of the results of Table 2, the HOMO energy levels of the Z -isomers of Cpds. 3a, 3b, 3c, 9 and 10 in the solvent phase have been observed at -6.08, -6.35, 6.07, -6.11 and -6.24 eV, respectively, and their corresponding LUMO energy levels have been located at -2.90, -3.18, -2.89, -2.92 and -2.97 eV, respectively. Similarly, The HOMO energy levels of the E-isomers of Cpds. 3a, 3b, 3c, 9 and 10 have been seen at 6.01, -6.28, -5.99, -6.04 and -6.16 eV, respectively, and their corresponding LUMO energy levels have been located at -2.93, -3.21, -2.92, -2.95 and -3.01 eV, respectively. 8

These results display that the HOMO energy levels of the Z-isomers of all the molecules are lower than the HOMO energy levels of their E-isomers, while, the LUMO energy levels of their Z-isomers are somewhat higher than their E-isomers. Therefore, the HLG values of the Z-isomers of all these molecules are larger than those of the E- isomers and the HLG values of all these compounds are almost close to each other. On the basis of the above information, the HOMO and LUMO energy levels of both Z- and E-isomers of Cpd. 3b with R1=CO2Me and R2=COOMe, have been observed lower than the other molecules and the HOMO and LUMO energy levels of both isomers of Cpd. 3c with R1=OCH2CO2tBu and R2=COOMe are slightly higher than the other molecules.

3.3. Natural charge distributions and Molecular electrostatic potential (MEP) The natural population analysis (NPA) atomic charges for both Z- and E-isomers of all the bifunctional hemithioindigo chromophores have been calculated with B3LYP/6311+G** method in methanol solvent. The natural atomic charges of some of the atoms with more negative and more positive charges and the natural charges of stilbene-part and thioindigo-part of each molecule, which are the sum of every atomic natural charge in these groups, are listed in Table 3. The NPA atomic charges show that the highest negative atomic charges of Cpds. 3a-3c have been observed for O33, O34 and O36 atoms of the stilbene-part of the molecules, respectively, and the highest positive atomic charges of Cpds. 3a-3c have been observed for C32, C11 and C35 atoms of the molecules, respectively. In Cpds. 9 and 10, the highest negative atomic charges have been observed for O12 atom of the carboxy group of the molecules, but the C32 atom of the carboxy group of Cpd. 9, shows the most positive atomic charge and the C32 atom 9

of Cpd. 10 which is linked to the N31 atom of the molecule, shows the most positive atomic charge among the other atoms. Also, among all the H atoms of Cpds. 9 and 10, the H atoms of the carboxy groups shows the highest positive atomic charge. Moreover, the stilbene-part of the molecules which are the region bearing the donating group of the molecules shows positive natural charge, while the thioindigo-part which are the region bearing the acceptor group shows negative natural charge. For all these molecules, the natural charges of stilbene-part of E-isomers of the molecules are higher than the Zisomers that means that the aromatic ring that connected to the R1 groups, acts as an electron donor. For E-isomers of these molecules, the net charge of stilbene-part of the molecules is in decreasing order: 9 (0.22556) > 3c (0.22499) > 3a (0.22228) > 10 (0.19959) > 3b (0.13598), and this order for Z-isomers of these molecules are: 3c (0.21029) > 9 (0.20986) > 3a (0.20779) > 10 (0.18606) > 3b (0.11936). It means that the stilbene-part of Cpds. 9 and 3c, show relatively the stronger electron donating property. Molecular electrostatic potential (MEP) is a useful way to study the charge distributions of molecules as three dimensional which information about the charge distributions can be used to identify how molecules interact with one another and also to specify processes based on the ‘‘reco nition’’ o one compound by another, as in en yme– substrate and drug-receptor interactions. This counter map is an appropriate way to distinguish both electrophilic and nucleophilic reactive sites of molecules for study of biological systems [41-43]. The MEP for both Z- and E-isomers of the molecules at the B3LYP/6-311+G** optimized geometry with the electron density isosurface of 0.0004 a.u. have been presented in Fig. 3. Commonly, the various values of the electrostatic potential are distinguished by different colors. The potential values increase as follows: red < orange < yellow < green < blue. The red and yellow colors on MEP map, show

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the negative regions of the molecule which are suitable area for electrophilic reaction, especially the red color which is the preferred site for electrophilic reaction. While, the blue color on this map show the appropriate sites for nucleophilic reactions. The MEP maps of all these molecules show that the red and yellow colors or negative charges are more focused around the oxygen atoms of the molecules because of the more electronegativity of O atoms which shows that these regions of the molecules are appropriate regions for electrophilic reactions. The blue color or positive charges are focused on the over the hydrogen atoms of the carboxy group of the Cpds. 9 and 10 which shows that these regions are the suitable sites for nucleophilic reactions. According to Fig. 3, the color code of the Z-isomers of Cpds. 3a,3b,3c,9 and 10 are between -0.06388 and +0.06388; -0.05689 and +0.05689; -0.06456 and +0.06456; 0.07370 and +0.07370; and -0.07305 and +0.07305, respectively, and also, for the Eisomers of Cpds. 3a,3b,3c,9 and 10 are between -0.05577 and +0.05577; -0.05878 and +0.05878; -0.05620 and +0.05620; -0.07224 and +0.07224; and -0.06972 and +0.06972, respectively. These data show that for both isomers of these molecules, the electrostatic potential values of Cpd. 9 and 10 are higher than the other molecules which are in accordance with the strength of electron donating groups and the stronger electron accepting group of COOH of these compounds. For all of the molecules, except Cpd. 3b, the electrostatic potential values of the Z-isomers are higher than the E-isomers.

3.4. Nonlinear optical properties and other molecular properties In order to study the relationships among molecular structures and nonlinear optical properties (NLO) of the bifunctional hemithioindigo chromophores, the polarizability (α), first hyperpolarizabilitiy (β) and second hyperpolari ability (γ) of all these 11

molecules have been obtained by the frequency calculation at the B3LYP/6-311+G** level in methanol. Dipole moment, polarizability and first hyperpolarizability are important physical quantities of organic molecules that could be affected by changing the molecular structure. The nonlinear optical (NLO) properties are beneficial properties in data storage and electro-optic applications [44]. The second hyperpolari ability (γ), is the microscopic origin of third-order nonlinear optical (NLO) property which can be obtained from hexadecapole moment components [45-47]. The total dipole can be applied as a descriptor to display the charge transfer inside the molecule and can be obtained by the vector components of dipole moment [41,48,49]. Polarizability (α) and first hyperpolarizability (βtot) demonstrate the reaction of a molecule in an electric field and can be obtained from the tensor components of polarizability and tensor components of hyperpolarizability, which can be obtained using a frequency calculation in Gaussian [41,48,50]. The chemical potential (ρ), chemical hardness (η) and so tness (σ), electronegativity (χ) and electrophilicity index (ω) o a molecule are chemical reactivity descriptors which have been computed by Koopman’s theorem [51-53]. At fixed external potential V(r), the first and the second derivative of total energy (E) of a molecule with respect to the number of electrons (N) is defined as the chemical potential (ρ), and the hardness of a molecule, respectively [54,55]. electronegativity (χ) can be obtained by the following equation [54,55]: χ= 

1 ( E HOMO  E LUMO ) 2

(2)

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The chemical hardness (η) is a measure of the resistance of a molecule to charge transfer and has been related to the stability and reactivity of a molecule, can be computed by the following equation:

1 1 η= [ IP  EA]  [ E LUMO  E HOMO ] 2 2

(3)

which IP≈EHOMO and EA≈ELUMO which EA is defined as electron a finity and IP is defined as ionization potential [41,50,54]. The chemical softness, which is defined as the inverse of the chemical hardness, σ =

1 , 

determines the capacity of a molecule to attract electrons and identify simplicity of charge transfer. The chemical softness has been associated to the polarizability values. It means that the soft and hard molecules have high and low polarizability, respectively [41,54,56]. The electrophilicity index (ω) which measures the affinity of chemical molecules to attract electrons, can be calculated by the following equation [41,56]:



2 2

(4)

The polarizability values and these global quantities, have been recognized as proper quantities for an explanation of the chemical reactivity of a molecule [47,54]. All these parameters for both Z- and E-isomers of the bifunctional hemithioindigo chromophores in the solvent phase calculated with the B3LYP/6-311+G** method has been gathered in Table 4. For all the molecules, dipole moment values of the Z-isomers are higher than the E-isomers and both isomers of Cpds. 3b and 10 have higher μ values compared to the other compounds. Since the higher dipole moment in a molecule,

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displays the strong intermolecular interactions [41], the Z-isomer of Cpds. 3b and 10 show the strongest intermolecular interactions relative to the other molecules. The results of Table 4 indicate that the polarizability and hyperpolarizability values ( α and βtot) of E-isomers of the molecules are higher than the Z-isomers. These values for both isomers of these molecules decreased in the order of 3c > 3b > 3a > 9 > 10. Comparing α and β values of Cpds. 3a-3c and 9-10, shows that Cpds. 3a-3c with a slightly weaker acceptor group (R2=COOMe) have larger α and β values than Cpds. 910 with slightly the stronger acceptor group (R2=COOH). As well as, both isomers of Cpd. 10 show the smallest α and β values among the other molecules. Also, switching ratios (γZ / γE) [45] of all the compounds shows that this value for Cpd. 3c is larger than the other compounds and for Cpd. 10 is smaller than the other compounds. These results show that Cpd. 3c has the highest NLO properties compared to the other molecules and is the most efficient NLO switch among the hemithioindigo chromophores treated here, which this result is in accordance with the other molecular properties (chemical softness) which have been discussed in the following. Chemical hardness of a molecule determines the charge transfer and the chemical reactivity of the molecule. Hard molecules with higher chemical hardness show the less reactivity than the soft molecules with smaller chemical hardness [41,56,57]. As seen in Table 4, chemical hardness of all the molecules is almost close to each other and the chemical softness of Cpds. 3b and 3c are a little more than the other molecules. For all of the molecules, the chemical hardness of the Z-isomers are larger than the E-isomers, while, the chemical softness of the E-isomers are higher than the Z-isomers. It means that the charge transfer and the chemical reactivity of the E-isomers of the molecules are easier than the Z-isomers which can be attributed to the better electron donating property of the E-isomers of the molecules.

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According to the polarizability and hyperpolarizability and chemical hardness values, an inverse relationship between α, βtot values and the chemical hardness (η) of the molecules has been observed, practically. The less chemical hardness of Cpds. 3b and 3c and therefore the higher chemical softness of them, shows that the electron density of these molecules is more easily influenced and the molecules would be more reactive. The higher polarizabilities values of these molecules indicate that these molecules increases the distortion o the electron cloud by an electric field and causes a higher intramolecular charge transfer ability [58,59]. As observed in Table 4, the order of absolute value o chemical potential (σ), the electronegativity (χ) and the electrophilicity index (ω) of both isomers of these molecules is identical and the order of these values is 3b > 10 > 9 > 3a > 3c. It shows that Cpd. 3c, with relatively the strongest electron donating group, has the smallest χ, σ and ω values. The electronegativity and absolute value of chemical potential of the Zisomers of the molecules are larger than the E isomers, while the electrophilicity index of the E-isomers are higher than the Z-isomers. It means that the affinity of the Eisomers of the chemical molecules to attract electrons is higher than the Z-isomers. Concerning to these results, it is clear that the chemical hardness, electronegativity, absolute value of the chemical potential and electrophilicity index of both isomers of Cpd. 3c is smaller than those of the other molecules, while NLO properties and the chemical softness of Cpd. 3c is higher than the other molecules. Therefore, the E-isomer of Cpd. 3c, shows the best chemical reactivity on the basis of these chemical reactivity descriptors, relatively.

3.5. Electronic absorption spectra

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The absorption properties such as excitation energies, maximum wavelengths (λmax), oscillator strengths (f), main transition and its electronic transition confi urations and the lifetime of the first excited state of both Z- and E-isomers of all the bifunctional hemithioindigo chromophores calculated through TDDFT calculations by B3LYP/6311+G** method in methanol solvent, are gathered in Table 5. Also, the simulated absorption spectra of Z-isomers and E-isomers of each molecule with a Gaussian line broadening of 0.333 eV, which have been plotted by the Grace 5.1.23 software [60], have been presented in Fig. 4. Our calculations show that both isomers of all the molecules in the UV-Vis range, show two-three noticeable absorption bands. Three calculated absorption bands (λmax) of the E-isomer of Cpd. 3a have been observed at 464.75 nm with an oscillator strength f=0.2551, at 354.34 nm with an oscillator strength f=0.7344 and at 236.17 nm with an oscillator strength f=0.2252 Also, the λmaxs of the Z-isomer of this molecule have been found at 442.47 nm with an increased oscillator strength f=0.4168, at 351.90 nm with a reduced oscillator strength f=0.5371 and at 220.90 nm with an increased oscillator strength f=0.2479. The λmaxs and oscillator strengths of both isomers of the other molecules, which are shown in Table 5, show that similar properties have been observed in the absorption properties of the other molecules. It means that, the calculated absorption bands (λ maxs) of the E-isomers of all the molecules are higher than those of the Z-isomers. However, the E isomers show weaker oscillator strengths than the Z-isomers for the first transitions and third main transitions; and show higher oscillator strengths than the Z-isomers for the second main transitions. All the results are in qualitative agreement with the experimental results [4]. The structures of the frontier molecular orbitals associated with the main transitions of Z-isomers and E-isomers of all the molecules have been shown in Fig. 5 and Fig. 6, respectively. For both isomers of all the molecules, it is clear that the first transitions are

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attributed to the HOMO → LUMO (π→π*) transitions. For Cpds. 3a and 3c, the second transitions correspond to the HOMO → LUMO+1 (π→π*) transitions,

hile or the

other molecules correspond to the HOMO-1 → LUMO (π→π*) transitions. But, the third transitions of all the molecules correspond to different molecular orbital (π→π*) transitions. As shown in Figs. 5 and 6, since the frontier molecular orbitals are mainly composed of p atomic orbitals, so, all the electronic transitions correspond to π→π* transitions. According to the results of Table 5 and the calculated absorption spectra of both isomers of all the molecules, which are shown in Fig. 7, the order of the maximum absorption bands (λmaxs) related to the first transitions of both isomers (Vis range) of all the molecules is: 3b > 3c > 3a > 9 > 10. The order of the second absorption bands (near UV range) of both isomers as follows: 9 > 3c > 3a > 10 > 3b, which this order is almost in agreement with the experimental results [4]. Also, the order of the third absorption bands (UV range) of the Z- and E-isomers is: 3b > 3a > 3c > 9 > 10 and 3c > 9 > 3a > 10 > 3b, respectively. On the basis of the above results and the electron donating ability of the R1 groups in the stilben-part of all the molecules which as follows: 10 > 3c > 3a > 9 > 3b, and since electron accepting strength of R2=COOH is higher than R2=COOMe, we can conclude that the order of the second maximum absorption bands of both isomers of Cpds. 3a-3c with R2=COOMe group which is almost accordance with the experimental results and the order of the third maximum absorption bands of the E-isomers of Cpds. 3a-3c, depend on the strength of electron donating capability of the R1 groups. It means that among Cpds. 3a, 3b and 3c, the absorption bands shift to the longer wavelength by increasing the electron donating capability of the R1 groups. Comparing the calculated and experimental absorption bands of Cpds. 9 and 10 show that the calculated absorption bands are qualitatively in agreement with the

17

experimental results. However, the electron donating ability of R1 group in Cpd. 10 is slightly more than that of Cpd. 9, because of the high strength of electron accepting of the COOH group in these compounds, the maximum absorption bands of Cpd. 9 is higher than Cpd. 10. Also, In order to evaluate the solvatochromic behavior of these compounds by quantum chemical calculations, the absorption spectra of these compounds in methanol and dichloromethane (DCM) solvents have been obtained by TDDFT-B3LYP/6-311+G** method and compared to each other which have been shown in Fig. 8 and Table 6. In order to evaluate the solvent effect on the absorption spectra, we adopted the CPCM for DCM and methanol as the solvent model. The Solvatochromic effect or solvatochromic shift denotes to a strong dependence of absorption spectra with the solvent polarity. Since polarities of the ground and excited state of a chromophore are dissimilar, a variation in the solvent polarity will lead to different stabilization of the ground and excited states, and consequently, a variation in the energy gap between these electronic states. Thus, observation of variations in the position, intensity, and shape of the absorption spectra, as a result of the changing of solvent polarity, means that the chromophore has the solvatochromic behavior. It means that the excitation energies and therefore maximum absorption wavelengths are in principle changed by the solvents [61,62]. The results of Table 6 and Fig. 8 shows that the calculated maximum absorption wavelengths of all the compounds in methanol and DCM, except Cpd. 9 and 10, are slightly larger than the experimental values [4]. Also, for all the compounds, the maximum absorption wavelengths of the E-isomer is slightly larger than the Z-isomer. According to the results, Cpds. 3a-3c with the R2=COOMe group show slightly the higher solvatochromism switching behavior than Cpds. 9 and 10 with the R2=COOH group. For example, Cpd. 3c shows relatively the higher solvatochromism. Because, the

18

maximum absorption peak of Cpd. 3c shows the bathochromic shift ( 17 nm (for Eisomer) and 10 nm (for Z-isomer)). It means that the excitation energies and maximum absorption wavelengths are changed a little more than the other compounds, by the variation of the solvent polarity. Cpds. 9 and 10 show very small solvatochromism. Especially, the E-isomer of Cpd. 10 do not show the solvatochromism which is in agreement with the experimental results [4]. From these results, the shift of maximum absorption peak due to the solvent effect is predicted to depend on the donor and acceptor substituents. Cpds. 3a-3c having the COOMe group as the slightly weaker acceptor group, show the higher peak shift than those having the slightly stronger COOH acceptor group. Among Cpds.3a, 3b and 3c, Cpd. 3c which have the stronger donating group, shows slightly the higher peak shift or the higher solvatochromism switching behavior. The lifetime of the first excited state (τ) of an organic molecule, which is a main factor for estimating the e ficiency o char e trans er, can be calculated from the following equation:

(5)

Which Ak,k′ is instein coe ficient or spontaneous emission, ћ, c and e are the reduced Planck’ s constant, the speed of light in vacuum, and the elementary charge, respectively. Also, rk,k′ and ∆Ek,k′ are transition dipole moment and the transition energy from states k to k′, respectively [63-66]. The calculated li etime o the first excited state of both isomers of all the molecules has been presented in Table 5. It can be found that, the order of the lifetime values of the Z-isomers of all the molecules is: 3b (9.92 ns) > 10 (9.08 ns) > 9 (7.25 ns) > 3a (7.03 ns) > 3c (6.79 ns). Also, the order of the lifetime 19

values of the E-isomers of all the molecules is: 10 (17.16 ns) > 3b (16.48 ns) > 9 (13.29 ns) > 3a (12.68 ns) > 3c (12.14 ns). Therefore, for both isomers of Cpds. 3a-3c, the order of the τ values is: 3b > 3a > 3c, which can be concluded that for these molecules there is a reverse correlation bet een the τ values and the stren th o electron donatin of the R1 groups. Cpd. 3c which have slightly stronger electron donating group compared to the other molecules, speed up the isomerization reaction which is in accordance with the higher charge transfer of this molecule and smaller τ values. Also, the slowest lifetime among these molecules has been observed for Cpds. 3b and 10, that means that Cpd. 3b with the weakest electron donating R1 group show the slowest reaction and charge transfer. Also, comparing the lifetime of Z- and E-isomers of these molecules show that the E-isomers have higher τ values than the Z-isomers. It means that the reaction and charge transfer of the Z-isomer of these molecules are faster than the E-isomers.

3.6. Thermodynamic properties The thermodynamic quantities such as total thermal energy (E), heat capacity (C), entropy (S), and enthalpy change (∆H) of both isomers of all the bifunctional hemithioindigo chromophores which have been calculated with the frequency calculations at the B3LYP/6-311+G** level of theory in methanol solvent has been listed in Table 7. A minimum structure of all the molecules must be obtained and used for estimation of thermodynamic quantities because the vibrational partition function can be influenced by the frequencies. The entropy (S), internal thermal energy (E) and heat capacity (C) which can be obtained from the related equations and the more information about thermochemistry quantities accomplished by Gaussian, are given in

20

Refs. 67-69 [67-69]. As seen in Table 7, for both Z- and E-isomers of all the molecules, all the obtained thermodynamic parameters are almost close to each other and do not show pronounced changes. All thermodynamic quantities of both isomers of these molecules decreased as 3c > 9 > 10 > 3a > 3b. Since Cpd. 3c has higher NLO properties and higher hyperpolarizability, we can conclude that the higher thermodynamic quantities of both isomers of this molecule can be associated to the better reactivity of this molecule.

4. Conclusions In this study, the Z- and E-isomers of a novel class of bifunctional hemithioindigo chromophores have been studied by DFT and TDDFT calculations. The molecular structures, energetic properties, NPA and MEP analysis, nonlinear optical properties, switching

ratios,

UV-Vis

absorption

spectra,

solvatochromic

behavior

and

thermodynamic properties of both isomers of these chromophores, have been considered via quantum computational methods for comparison of the obtained quantities of both isomers of the molecules and clarify why Cpd. 3c is relatively the best reactive molecule among the other molecules. As a result of the molecular structure analysis, we can conclude that both isomers of the molecules are almost planar around the famous dihedral angles. The energetic properties show that the EHOMO and ELUMO levels of both isomers of Cpd. 3c are higher than those of the other molecules, and these values for both isomers of Cpd. 3b are lower than the other molecules, which the higher HOMO and LUMO energy levels of Cpd. 3c is in accordance with the more strength of the electron donating property of this molecule. NPA and MEP analysis show that the electrostatic potential values of Cpds. 9 and 10 with the stronger acceptor group

21

(R2=COOH) are higher than Cpds. 3a-3c with the weaker acceptor group (R2=COOMe). The optical and molecular properties of these molecules show that the NLO properties of Cpd. 3c is higher than the other molecules, while the chemical hardness, electronegativity, absolute value of chemical potential and electrophilicity index of both isomers of this molecule is smaller than those of the other molecules that means that this compound shows the best chemical reactivity on the basis of these chemical reactivity descriptors and the highest switching ratios and therefore the best NLO switch among the other chromophors. TDDFT calculation results show that among Cpds. 3a, 3b and 3c, the absorption bands shift to the higher wavelength by increasing the electron donating ability of the R1 groups. The calculated lifetime of the first excited state o both isomers o all the molecules sho s that among Cpds. 3a-3c, the order o the τ values is: 3b > 3a > 3c, which can be concluded that for these molecules there is a reverse correlation bet een the τ values and the stren th o electron donating of the R1 groups. Also, the slowest lifetime among these molecules has been observed for Cpds. 3b and 10, that means that Cpd. 3b with the weakest electron donating R1 group show the slowest reaction and charge transfer and the reaction and charge transfer of the Z-isomer of these molecules are faster than the E-isomers. Also, Cpd. 3c shows the higher solvatochromism because of the higher peak shift due to the variation of solvent polarity. Cpd. 3c shows the higher thermodynamic quantities of both isomers of the molecule which can be associated to the better reactivity of this molecule. We can conclude that the higher thermodynamic quantities, the higher chemical softness, the higher NLO properties, the higher solvatochromic behavior and the larger absorption maximum of both isomers of Cpd. 3c can be attributed to the better reactivity of this molecule and this compound is the most efficient chromophore among the other chromophores studied here. Therefore, we obtained guiding principle

22

for the design of the solvatochromic chromophores. The present results for the design of new hemithioindigo chromophores based on the studied hemithioindigo switch, shows that the E-isomer of hemithioindigo chromophores with the slightly higher electron donating group in the stilbene part and the weaker electron accepting group in the thioindigo-part could be more efficient chromophore, relatively which can be designed by modifying the donor/acceptor substituents and/or photochromic molecular structure.

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28

Figure captions: Figure. 1. Structures of the bifunctional hemithioindigo chromophores. Compounds have been described in Ref. [4]

Figure. 2. Optimized molecular structures of Z- and E-isomers of the bifunctional hemithioindigo chromophores at the B3LYP/6-311+G** level in the solvent phase.

Figure. 3. MEP maps of both isomers of the bifunctional hemithioindigo chromophores.

Figure. 4. Electronic absorption spectra of Z- and E-isomers of each of the bifunctional hemithioindigo chromophores with TDDFT calculations using B3LYP/6-311+G** method in the solvent phase.

Figure. 5. Frontier molecular orbitals of Z-isomers of all the bifunctional hemithioindigo chromophores along with the molecular orbital energy levels calculated at B3LYP/6-311+G** level in the solvent phase.

Figure. 6. Frontier molecular orbitals of E-isomers of all the bifunctional hemithioindigo chromophores along with the molecular orbital energy levels calculated at B3LYP/6-311+G** level in the solvent phase.

Figure. 7. Calculated electronic absorption spectra of both isomers of all the bifunctional

hemithioindigo

chromophores,

with

TDDFT-B3LYP/6-311+G**

calculations in methanol.

Figure. 8. Calculated absorption spectra of all the bifunctional hemithioindigo chromophores in methanol and DCM, with TDDFT-B3LYP/6-311+G** method.

29

Table

Table 1 Selected geometrical parameters of Z and E isomers of the bifunctional hemithioindigo chromophores at B3LYP/6 311+G** level in the solvent phase. Compound

R(S7-C8)

R(C8-C13)

R(C13-C14)

A(S7-C8-C13)

A(C8-C13-C14)

D(S7-C8-C13-C14)

D(C9-C8-C13-C14)

3a Z

1.781

1.355

1.447

128.1

132.7

-0.132

-179.9

E

1.803

1.364

1.450

116.7

135.5

-180.0

0.000

Z

1.776

1.352

1.453

128.6

132.2

-0.027

-179.9

E

1.799

1.359

1.458

116.8

135.4

180.0

0.000

Z

1.781

1.355

1.447

128.0

132.7

-0.155

-179.9

E

1.803

1.364

1.449

116.7

135.5

180.0

0.000

Z

1.781

1.355

1.447

128.1

132.7

-0.008

-179.9

E

1.803

1.364

1.449

116.7

135.5

180.0

0.000

Z

1.781

1.354

1.451

128.1

132.5

0.224

179.8

E

1.803

1.362

1.454

116.7

135.5

-179.7

0.1410

3b

3c

9

10

Notes: Bond distances (in Å), angles (in degrees)

Table

Table 2 EHOMO (eV), ELUMO (eV), HLG (eV), total energy (eV) and relative energy ΔE = E Z - E E (eV) of Z and E isomers of the bifunctional hemithioindigo chromophores with B3LYP/6-311+G** method in the solvent phase. Compound

EHOMO

ELUMO

HLG

Total energy

Z

-6.08

-2.90

3.18

-44129.319

E

-6.01

-2.93

3.08

-44129.136

Z

-6.35

-3.18

3.17

-41012.072

E

-6.28

-3.21

3.06

-41011.884

Z

-6.07

-2.89

3.18

-47339.818

E

-5.99

-2.92

3.07

-47339.633

Z

-6.11

-2.92

3.19

-41989.959

E

-6.04

-2.95

3.09

-41989.764

Z

-6.24

-2.97

3.27

-45730.033

E

-6.16

-3.01

3.15

-45729.836

Relative energy ΔE = E Z - E E

3a -0.183

3b -0.188

3c -0.185

9 -0.195

10 -0.197

Table

Table 3 Natural charges of different groups and the most negative and the most positive charges of atoms of Z and E isomers of the bifunctional hemithioindigo chromophores in the solvent phase. 3a-Z

3a-E

3b-Z

3b-E

3c-Z

3c-E

9-Z

9-E

10-Z

10-E

S7 = 0.38116

S7 = 0.38779

S7 = 0.40484

S7 = 0.39906

S7 = 0.38100

S7 = 0.38737

S7 = 0.38430

S7 = 0.39321

S7 = 0.38643

S7 = 0.39481

C9 = 0.51381

C9 = 0.50428

C9 = 0.53156

C9 = 0.50543

C9 = 0.51344

C9 = 0.50385

C9 = 0.51401

C9 = 0.49379

C9 = 0.59752

C9 = 0.49838

O10 = -0.61772

O10 = -0.61837

O10 = -0.59750

O10 = -0.59880

O10 = -0.61834

O10 = -0.61905

O10 = -0.61585

O10 = -0.61781

O10 = -0.60682

O10 = -0.61004

C11= 0.80970

C11= 0.80957

C11= 0.81000

C11= 0.80951

C11= 0.80968

C11= 0.80951

C11= 0.80194

C11= 0.80102

C11= 0.80208

C11= 0.80115

O12= -0.54447

O12= -0.54471

O12= -0.54350

O12=-0.54387

O12= -0.54452

O12= -0.54479

O12= -0.68480

O12= -0.68584

O12= -0.68468

O12= -0.68547

O20= -0.63173

O20= -0.63428

O20= -0.63068

O20= -0.63279

O20= -0.63175

O20= -0.63432

O20= -0.63099

O20= -0.63355

O20= -0.63059

O20= -0.63305

O21= -0.53403

O30= -0.53392

C21= 0.80542

C30= 0.80569

O33= -0.53214

O33= -0.53246

O21= -0.53511

H24= 0.50698

H25= 0.50766

H24= 0.50713

C32= 0.81186

C32= 0.81172

O34= -0.63579

O34= -0.63577

C35= 0.81559

C35= 0.81560

H25= 0.50744

O30= -0.53457

N31= -0.64692

N31= -0.64671

O33= -0.63668

O33= -0.63677

O35= -0.54628

O35= -0.54675

O36= -0.64452

O36= -0.64481

C32= 0.80433

C32= 0.80425

C32= 0.93420

C32= 0.93421

O34= -0.53142

O34= -0.53147

-----------------

-----------------

O37= -0.56922

O37= -0.56909

O33= -0.63079

O33= -0.63106

O33= -0.70815

O33= -0.70818

-----------------

-----------------

-----------------

-----------------

C39= -0.58879

C39= -0.58869

O34= -0.67032

O34= -0.67027

O34= -0.60641

O34= -0.60669

-----------------

-----------------

-----------------

-----------------

C40= -0.60815

C40= -0.60814

H37= 0.50708

H37= 0.50702

C36= -0.58619

C36= -0.58613

-----------------

-----------------

-----------------

-----------------

C41= -0.60820

C41= -0.60814

-----------------

-----------------

C37= -0.60665

C37= -0.60677

-----------------

-----------------

-----------------

-----------------

-----------------

-----------------

-----------------

-----------------

C38= -0.60678

C38= -0.60680

Stilbene-part

Stilbene-part

Stilbene-part

Stilbene-part

Stilbene-part

Stilbene-part

Stilbene-part

Stilbene-part

Stilbene-part

Stilbene-part

0.20779

0.22228

0.11936

0.13598

0.21029

0.22499

0.20986

0.22556

0.18606

0.19959

Thioindigo-part

Thioindigo-part

Thioindigo-part

Thioindigo-part

Thioindigo-part

Thioindigo-part

Thioindigo-part

Thioindigo-part

Thioindigo-part

Thioindigo-part

-0.20779

-0.22228

-0.11936

-0.13598

-0.21029

-0.22499

-0.20986

-0.22556

-0.18606

-0.19959

Table

Table 4 Dipole moment μ (Debye), mean polarizability α, total hyperpolarizability βtot, chemical hardness η, chemical softness σ (eV), Electronegativity (χ), Chemical potential (ρ), Electrophilicity index (ω) values, second hyperpolarizability γ( γxxxx ) and switching ratio (γZ / γE) of Z and E isomers of the bifunctional hemithioindigo chromophores calculated with the B3LYP/6-311+G** method in the solvent phase. Compound

μ

α (10-22 esu)a

βtot (10-28 esu)a

η

σ

χ

ρ

ω

γ / a.u.

γZ / γ E

3a Z

2.68

0.647

0.996

1.592

0.6281

4.49

-4.49

6.33

104339.24

E

1.66

0.661

1.390

1.540

0.6493

4.46

-4.46

6.48

26215.889

Z

6.74

0.658

1.020

1.587

0.6300

4.76

-4.76

7.16

110105.85

E

4.80

0.694

1.403

1.533

0.6522

4.74

-4.74

7.35

26920.745

Z

2.59

0.729

1.120

1.588

0.6294

4.48

-4.48

6.32

113430.01

E

1.83

0.734

1.421

1.537

0.6504

4.46

-4.46

6.47

27266.828

Z

2.11

0.636

0.998

1.594

0.6270

4.52

-4.52

6.41

97098.61

E

0.78

0.660

1.386

1.543

0.6478

4.50

-4.50

6.56

25485.19

Z

5.34

0.629

0.438

1.633

0.6120

4.60

-4.60

6.49

95307.47

E

3.40

0.658

0.543

1.576

0.6344

4.58

-4.58

6.66

25280.49

3.98

3b 4.09

3c 4.16

9 3.81

10

a

(α; 1 a.u. = 1.48176 *10

-25

esu, β; 1 a.u. = 8.63993 * 10

-33

esu)

3.77

Table

Table 5 Calculated spectroscopic properties including excitation energies (eV)/maximum wavelengths (λmax) (nm), oscillator strengths (f), lifetimes for the first excited states (τ)(ns), main transition and its electronic transition configurations of the E and Z isomers of the bifunctional hemithioindigo chromophores in methanol, with the TDDFT-B3LYP/6-311+G** method. Compound

state

excitation energies (eV)/λmax (nm)

f

lifetime (ns)

main transition(electronic transition

configurations)

3a E 1 4 18

2.66 / 464.75 3.49 / 354.34 5.25 / 236.17

0.2551 0.7344 0.2252

12.68 2.56 3.71

H→L (96.31%) π→π* H→L+1 (76.69%) π→π* H-4→L+2 (47.46%) π→π*

1 4 23

2.80 / 442.47 3.52 / 351.90 5.61 / 220.90

0.4168 0.5371 0.2479

7.03 3.45 2.94

H→L (95.63%) π→π* H→L+1 (73.25%) π→π* H-1→L+2 (33.71%)

1 4 21

2.59 / 478.64 3.64 / 340.60 5.34 / 232.09

0.2082 1.1001 0.1616

16.48 1.58 4.99

H→L (96.95%) π→π* H-1→L (73.25%) π→π* H-4→L+1 (48.14%)

1 4 23

2.71 / 456.15 3.66 / 337.94 5.51 / 224.72

0.3140 0.8741 0.2198

9.92 1.95 3.44

H→L (96.11%) π→π* H-1→L (72.85%) π→π* H-3→L+2 (24.59%

1 4 17

2.66 / 465.05 3.49 / 355.11 5.22 / 237.18

0.2668 0.7347 0.1625

12.14 2.57 5.18

H→L (96.33%) H→L+1 (77.83%) H→L+4 (35.23%)

1 4 25

2.79 / 442.98 3.51 / 352.75 5.61 / 220.82

0.4325 0.5397 0.2516

6.79 3.45 2.90

H→L (95.69%) π→π* H→L+1 (74.05%) π→π* H-1→L+2 (33.78%) π→π*

1 4 18

2.67 / 463.16 3.46 / 358.21 5.24 / 236.41

0.2418 0.8670 0.2240

13.29 2.21 3.74

H→L (96.35%) H-1→L (50.85%) H-4→L+1 (51.48%)

π→π* π→π* π→π*

1 4

2.81 / 441.20 3.48 / 355.33

0.4021 0.6084

7.25 3.11

H→L (95.70%) H-1→L (62.45%)

π→π* π→π*

Z

3b E

Z

3c E π→π* π→π*

Z

9 E

Z

26

5.75 / 215.61

0.3397

2.05

H-8→L+1 (56.20%)

π→π*

1 4 20

2.69 / 459.65 3.58 / 345.67 5.25 / 235.88

0.1844 0.8949 0.1630

17.16 2.00 3.96

H→L (96.66%) H-1→L (77.75%) H→L+4 (44.87%)

π→π* π→π* π→π*

2.83 / 437.02 3.62 / 342.16 5.84 / 212.29

0.3148 0.7001 0.2103

9.08 2.50 4.14

H→L (95.82%) H-1→L (78.99%) H-11→L (51.45%)

π→π* π→π* π→π*

10 E

Z 1 4 30

Table

Table 6 Calculated absorption peaks in methanol and dichloromethane (DCM) (in nm) and peak shifts between in DCM and in methanol solutions (in nm) of 3a-3c and 9 and 10 with the TDDFT-B3LYP/6-311+G** method. Compound

peaks in methanol (nm)

peaks in DCM (nm)

Peak shift (nm)

λmax (exp) in methanol

λmax (exp) in DCM

3a E

464

455

13

457

450

Z

442

449

7

438

440

E

478

470

8

-

447

Z

456

440

16

-

438

E

465

448

17

-

-

Z

442

439

10

-

-

E

463

461

2

461

-

Z

441

437

4

444

-

E

459

459

0

450

450

Z

437

435

2

442

438

3b

3c

9

10

Table

Table 7 Thermodynamic properties of Z and E isomers of the bifunctional hemithioindigo chromophores, at the B3LYP/6-311+G** level in the solvent phase at T=298.15K. Compound

Total thermal energy (E)

Heat Capacity (C) -1

-1

Entropy (S) -1

-1

Enthalpy changes (ΔH)

(kcal mol -1)

(kcal mol -1)

(cal mol K )

Z

216.955

91.877

179.869

217.530

E

216.978

91.867

179.082

217.553

Z

195.093

83.429

165.528

195.670

E

195.114

83.418

164.830

195.695

Z

271.522

108.550

197.550

272.090

E

271.542

108.539

198.256

272.113

Z

264.791

106.375

193.945

263.363

E

264.813

106.356

193.706

263.386

Z

261.450

104.371

191.201

262.021

E

261.472

104.267

190.501

262.044

(cal mol K )

3a

3b

3c

9

10

Figure

Z-Isomer

E-Isomer

R2=COOMe

R2=COOH

R1=OCH2CO2Me

(3a)

R1=OCH2COOH (9)

R1=CO2Me

(3b)

R1=CH2NHCOOtBu (10)

R1=OCH2CO2tBu

(3c)

Figure

Z-isomer

3a

3b

3c

9

10

E-isomer

Figure Compound

3a

3b

3c

9

Z

E

10

Figure

Figure

3a (Z-isomer)

3b (Z-isomer)

3c (Z-isomer)

9 (Z-isomer)

LUMO+1

10

(Z-isomer)

------------------------------

LUMO+2

LUMO+2

LUMO+1

LUMO

LUMO +1

LUMO

LUMO

LUMO

HOMO

LUMO

HOMO

HOMO

HOMO-1

HOMO-1

HOMO-8

HOMO-11

HOMO

HOMO-1

HOMO-1

HOMO-3

LUMO +2

HOMO

HOMO-1

Figure

3a (E-isomer)

3b (E-isomer)

3c (E-isomer)

9 (E-isomer)

10

(E-isomer)

----------------------LUMO+2

LUMO+1

LUMO+4

LUMO+1

LUMO+1

LUMO

LUMO +1

LUMO

LUMO+4

LUMO

HOMO

LUMO

HOMO

LUMO

HOMO-1

HOMO

HOMO-1

HOMO

HOMO-4

HOMO-1

HOMO

-------------------------------------

HOMO-4

HOMO-4

Figure

Figure

Highlights 

Z- and E- isomers of some HTI-chromophores were studied by quantum methods.



Molecule 3c shows the higher NLO properties.



The slowest lifetime has been observed for molecules 3b and 10.

30

Graphical Abstract

31