Bromo-and chloro-derivatives of dibenzylideneacetone: Experimental and theoretical study of the first molecular hyperpolarizability and two-photon absorption

Accepted Manuscript Title: Bromo-and chloro-derivatives of dibenzylideneacetone: Experimental and theoretical study of the first molecular hyperpolarizability and two-photon absorption Authors: Francisco A. Santos, Luis M.G. Abeg˜ao, Ruben D. Fonseca, Aline M. Alcˆantara, Cleber R. Mendonc¸a, Marcelo S. Valle, M.A.R.C. Alencar, Kenji Kamada, Leonardo De Boni, J.J. Rodrigues Jr. PII: DOI: Reference:

S1010-6030(18)31066-9 https://doi.org/10.1016/j.jphotochem.2018.10.012 JPC 11528

To appear in:

Journal of Photochemistry and Photobiology A: Chemistry

Received date: Revised date: Accepted date:

24-7-2018 11-9-2018 4-10-2018

Please cite this article as: Santos FA, Abeg˜ao LMG, Fonseca RD, Alcˆantara AM, Mendonc¸a CR, Valle MS, Alencar MARC, Kamada K, De Boni L, Rodrigues JJ, Bromo-and chloro-derivatives of dibenzylideneacetone: Experimental and theoretical study of the first molecular hyperpolarizability and two-photon absorption, Journal of Photochemistry and amp; Photobiology, A: Chemistry (2018), https://doi.org/10.1016/j.jphotochem.2018.10.012 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Bromo-and chloro-derivatives of dibenzylideneacetone: experimental and theoretical study of the first molecular hyperpolarizability and twophoton absorption Francisco A. Santosa, Luis M.G. Abegãoa,f, Ruben D. Fonsecab,d, Aline M. Alcântarac,

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Cleber R. Mendonçab, Marcelo S. Vallec, M. A. R. C. Alencara, Kenji Kamadae, Leonardo De Bonib and J.J. Rodrigues Jr.a* a

Departamento de Física, Universidade Federal de Sergipe, 49100-000 São Cristovão, SE, Brazil

b

Instituto de Física de São Carlos, Universidade de São Paulo, CP 369, 13560-970 São Carlos, SP, Brazil

c

Departamento de Ciências Naturais, Universidade Federal de São João del Rei, 36301-160, MG,

Universidad popular del Cesar, Departamento de Fisica, Barrio Sabana, 2000004, Valledupar,

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d

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Brazil

Cesar, Colombia.

IFMRI, National Institute of Advanced Industrial Science and Technology, Ikeda, Osaka 563-

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e

f

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8577, Japan

Department of Radiology & Biomedical Imaging, Yale University, 330 Cedar St, New Haven,

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Connecticut 06520, USA

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* Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel.: +55-79-

Highlights

The first molecular hyperpolarizability (βHRS) of two DBA molecules was investigated Two-photon absorption cross-section (σ2PA) spectra of two DBA molecules were measured Calculated βHRS and σ2PA showed good accordance with the experimental results

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

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2105-6630; Fax: +55-79-2105-6630.

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 

Abstract: This work reports the study of the second- and third-order nonlinear optical properties of two dibenzylideneacetone derivatives: (1E,4E)-1,5-bis(4-bromophenyl)penta1,4-dien-3-one (4-DBDBA) and (1E,4E)-1,5-bis(4-chlorophenyl)penta-1,4-dien-3-one (4DCDBA) in dichloromethane solution. The nonlinear optical properties investigated were

the first molecular hyperpolarizability and the two-photon absorption (2PA) cross-section by using the hyper-Rayleigh scattering (HRS) and Z-scan techniques respectively. The values of the first molecular hyperpolarizability obtained by HRS ( 𝛽𝐻𝑅𝑆 ) were 25 × 10−30 cm4 statvolt −1

for

4-DBDBA

whereas

for

4-DCDBA

was

27 ×

10−30 cm4 statvolt −1. The peak value for 2PA cross-section by the spectral measurement

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was around 24 GM for 4-DBDBA and 17 GM for 4-DCDBA. In addition, quantum

chemical calculations were performed to support the interpretation from experimental results.

Keywords: dibenzylideneacetone derivatives; organic molecules; first molecular

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hyperpolarizability; two-photon absorption; hyper-Rayleigh scattering; Z-Scan 1. INTRODUCTION

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Materials that exhibit nonlinear optical (NLO) effects can be employed in several

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applications such as: optical switches [1], optical limiting [2], 3D microfabrication [3], two-

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photon excited fluorescence microscopy [4], optical data storage [5] and photodynamic therapy [6]. In the search for optical materials for such applications, organic molecules have been widely explored in this area due to their high nonlinearity coupled with ultrafast

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response [7]. Moreover, the magnitude of this NLO response can be improved with some

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strategic changes in their molecular structure. Previous works have shown that molecules with large conjugated structure and donor or acceptor groups linked to the structure's end

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tend to show larger nonlinear optical response [8-11]. Such changes in the molecular structure result in greater electronic delocalization, leading to higher hyperpolarizabilities.

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On the other hand, molecules with large molecular structure have usually a more complex and expensive synthesis process [12, 13]. Due to these conditions, many efforts have been

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done to design small molecules with large NLO response. In particular, dibenzylideneacetone (DBA) is an α,β-unsaturated ketone with two

aromatic rings interconnected by a conjugated bridge with a carbonyl group in the center [14]. These compounds were widely used as agents in biological activities such as antitumor, antimitotic and antiproliferative properties [15-17]. They have been also used as a sunscreen component [18, 19], due to its high coefficient of extinction in the violet region. Evidences were shown during the last years that these types of materials have

potential to be integrated in photonics devices [20-23]. Although such works have presented results on the second harmonic generation (SHG) achieved by the powder method and two-photon absorption (2PA) obtained with nanosecond pulses, their first molecular hyperpolarizability in solution with picoseconds pulses and 2PA cross-section (σ2PA) spectra with femtosecond pulses have never been reported. It is of relevant

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importance to investigate these microscopic properties, so that one can understand how to optimize the NLO responses through the design of each molecule.

In the present study, we report the second- and third-order nonlinear optical properties of the 4-DBDBA and 4-DCDBA in dichloromethane solution. The first

molecular hyperpolarizability in solution (βHRS) was obtained by using the hyper-Rayleigh

scattering (HRS) technique with picosecond pulses, whereas the experimental σ2PA spectra

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were measured with femtosecond pulses by the Z-scan technique. The Sum-Over-States

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(SOS) approach was used to fit the experimental σ2PA spectra, which allows to determine the transition dipole moments. To support the experimental data, quantum chemical

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calculations (QCC) were made to obtain theoretical values of βHRS and σ2PA by employing

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the time-dependent density functional theory (TD-DFT).

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2. EXPERIMENTAL SECTION

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Structures of the studied molecules are shown in Fig. 1. The compounds were prepared through the following synthesis procedure: into a round-bottom flask, a solution of the

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aromatic aldehyde (1.41 g, 10 mmol) in ethanol (10 mL) was added to a solution of acetone (0.29 g, 5 mmol) in sodium hydroxide (0.40 g, 10 mmol) in ethanol (10 mL) at 0 ˚C and

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allowed to come to room temperature. The reaction mixture was stirred for 15 to 60 min and monitored by thin layer chromatography (TLC) to confirm consumption of the starting material. The precipitate was filtered and/or added a portion of cold mixture of

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ethanol/water, to force the recrystallization, to yield DBA derivatives (4-DBDBA, 88% yield, 1.72 g, 4.39 mmol; 4-DCDBA, 93% yield, 1.42 g, 4.68 mmol). The compounds were characterized by nuclear magnetic resonance (NMR) and infrared spectroscopies. The 1H NMR (500 MHz) and 13C NMR (125 MHz) spectra were recorded as solutions in CDCl3 on a Bruker spectrometer. The chemical shifts were expressed as  (in ppm) with respect to a

standard internal TMS reference (1H NMR). In the Supplementary material, 1H NMR, 13C

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NMR and infrared data have been provided.

Figure 1. Synthesis of bromo-and chloro-derivatives of dibenzylideneacetone.

The DBA derivatives were dissolved in dichloromethane in a concentration of about

10−5 mol L−1 for a UV visible absorption (i.e. one-photon absorption, 1PA) measurement.

The samples were hold in 10-mm fused quartz cuvettes and the spectra were recorded by

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using a Shimadzu UV-1800 spectrophotometer. Additionally, fluorescence emission was

carried out at room temperature with the same concentration and optical path-length by

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using a Hitachi F4500 fluorescence spectrophotometer. No evidences of any emission were

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observed.

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The βHRS was obtained by using an extension of the conventional HRS technique introduced by Franzen et al [22]. The excitation source employed was a Nd:YAG, Q-

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switched and mode-locked laser operating at the fundamental frequency (1064 nm) that provide pulses of 100 ps, in pulse trains containing 20 pulses (separated by approximately

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13 ns) with a repetition rate of 300 Hz. A mechanical shutter was used to block the laser beam during background determination and after the measurements, avoiding sample

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exposure for a long time to the pump. The maximum intensity of excitation was controlled by two crossed polarizers. The HRS signal was collected perpendicularly to the pump beam

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direction by a fast photomultiplier tube (PMT). To improve the signal-to-noise ratio, it was added a spherical mirror to collect part of the signal that is scattered in the opposite

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direction of the PMT. A 532 nm narrow bandpass filter (10 nm band width) was used to warrant that only the SHG is detected by the PMT. In order to avoid interference of any external light in the measured signal, the HRS experimental setup was isolated in a dark chamber. More detailed description related to the experimental setup can be found in Ref. [24].

The HRS signal originates from the contribution individual of the nonlinear scatterers. The magnitude of signal scattered by a single molecule at double-frequency (𝐼2𝜔 ) is related to an intensity of excitation (𝐼𝜔 ) by [25]: 2 2 〉 2 𝐼2𝜔 = 𝐺(𝑁𝑠 〈𝛽𝐻𝑅𝑆 𝑠 + 𝑁𝑐 〈𝛽𝐻𝑅𝑆 〉𝑐 )𝐼𝜔

(1)

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in which, G is a parameter related to the scattering geometry, local field factors at ω and

2ω, as well as other optical and instrumental conditions. N is the fractional concentration of 2 〉 the used samples and 〈𝛽𝐻𝑅𝑆 is the squared value of the orientationally-averaged first

hyperpolarizability. The subscripts s and c refer to the solvent and chromophore

2 〉 investigated, respectively. The 〈𝛽𝐻𝑅𝑆 is related to the molecular tensor components 〈𝛽𝑖𝑗𝑘 〉

through the polarization state of both fundamental and harmonic beams, the molecular

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symmetry and the geometry of the experimental setup [26]. In general, the collection of the

N

signal on frequency-doubled light scattered on HRS experiments is carried out

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perpendicular to the excitation. Assuming that the fundamental light beam propagation is in the X-direction and polarized in the Z-direction, then the average value of the βHRS can be

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calculated by the following expression [27, 28]:

(2)

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2 ⟩ 2 ⟩ ⟨𝛽𝐻𝑅𝑆 ⟩ = √⟨𝛽𝑍𝑍𝑍 + ⟨𝛽𝑋𝑍𝑍

2 〉 2 〉 in which, 〈𝛽𝑍𝑍𝑍 and 〈𝛽𝑋𝑍𝑍 are macroscopic averages. In this case, we adopted the

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laboratory system of reference by the X, Y and Z coordinates, and the molecular system of reference by the x, y and z coordinates [29]. These macroscopic averages were written as a function of the molecular first-order hyperpolarizability tensor components (molecular

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system of reference), as reported elsewhere [27, 30]. In order to obtain the σ2PA spectra in DBA derivatives dissolved in dichloromethane,

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we use wavelength-tunable femtosecond Z-scan technique on the open-aperture mode [31]. A Ti:sapphire laser (MXR-CLARK) delivering pulses with approximately 150 fs and operating at 1 kHz repetition rate was used as the excitation source for an optical parametric amplifier (Quantronix, model TOPAS, OPA) that provides pulses with approximately 120 fs in the wavelength range used on this work, 480 up to 790 nm. The OPA output was employed as the light source of the Z-scan measurements. To guarantee a

Gaussian beam spatial profile, a spatial filter was used. The samples were conditioned in fused silica cuvettes of 2 mm in optical path and translated through the focal plane of a convergent lens of 15 cm in focal length [24]. The well-known relationship between the normalized transmittance and position

T(z) =

1 √πq 0 (z, 0)

+∞ 2

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measured through Z-scan technique with a Gaussian beam spatial profile is given by [31]: ∫ ln[1 + q 0 (z, 0)e−τ ] dτ −∞

(3)

in which, q 0 (𝑧, 0) = 𝛼2 𝐼0 𝐿(1 + 𝑧 2 /𝑧02 )−1, 𝛼2 is the 2PA coefficient, 𝐼0 is the intensity of

the pulse, L is the optical path, 𝑧0 is the Rayleigh length, and z is the sample position. The

2PA cross-section values were obtained using σ2PA = ℎ𝜈𝛼2 /𝑁, in which ℎ𝜈 is the energy

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of the incident photon, and 𝑁 is the number of molecules per cm3 . The 𝜎 2PA values are

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molecule-1.

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1

N

usually expressed in Göppert-Mayer units (GM), in which 1GM =1×10-50 cm4 s photon-

3. THEORETICAL CALCULATION SECTION

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To confirm the allowed electronic transitions from both experimental 1PA and 2PA

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spectra, QCC were carried out at TD-DFT theory level using the Gaussian09 program package [32]. The equilibrium geometries of the model molecules were optimized at the CAM-B3LYP/6-311+G(d,p) level of theory and the optimized geometries are presented in

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Table S1 in the Supplementary material. Then TD calculations were performed on the optimized geometry, using the same functional and basis set. Transition dipole moments

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from the ground state to the j-th excited state (𝜇0𝑗 , j>0), transition dipole moments between excited states (𝜇𝑖𝑗 , 𝑖, 𝑗 > 0 and 𝑗 ≠ 𝑖), permanent dipole moments in the ground state (𝜇00 )

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and excited states (𝜇𝑗𝑗 , j>0) to obtain the dipole moments difference (Δ𝜇0𝑗 = 𝜇𝑗𝑗 − 𝜇00 , 𝑗 > 0 ), and the excitation energies were calculated by using the Tamm-Dancoff approximation (TDA) [33]. The lowest fifteen excited states were considered in the simulated spectrum and the SOS formulation used for the spectral simulation were reported previously [34].

To compute the first-order hyperpolarizability tensor (𝛽𝑖𝑗𝑘 ) the CAM-B3LYP/6311+G(d,p) level of theory was used to calculate the static and dynamic (frequencydependent) components of the respective tensor using the Gaussian09 program package [32], considering an incident wavelength of 1064 nm. The static and dynamic first hyperpolarizability values were obtained from the cartesian components of tensor

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calculated in the molecular frame following the relation presented in Table S2 on the Supplementary material.

4. RESULTS AND DISCUSSION

The 1PA spectra of the two DBA derivatives in dichloromethane solvent medium present a band located at approximately 330 nm with molar absorption coefficient (ε) of

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about 2×104 M-1cm-1 (2.31×104 M-1cm-1 at 332 nm for 4-DBDBA and 1.97×104 M-1cm-1 at

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326 nm for 4-DCDBA, Fig. S7 in the Supplementary material). The small bathochromic

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shift between the two samples was attributed to the electron-donating nature of the substituents groups Br and Cl where the former is stronger than the latter [22]. The broad

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shape of the absorption band suggests that two electronic transitions are superimposed. Spectral decomposition with Gaussian band-shape (Fig. 3) revealed the absorption band

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consists of the two components centered at 3.67 eV (338 nm) and 4.12 eV (301 nm) for 4-

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DBDBA and at 3.76 eV (329 nm) and 4.13 eV (300 nm) for 4-DCDBA (Table 2). The region of transparency for both compounds for wavelengths longer than 450 nm, make these samples extremely suitable for HRS measurement when excited with a

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pulsed laser at 1064 nm. To measure the HRS signal from both molecules, the external reference used to obtain experimental G was the molecular structure of 4-nitroaniline

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(PNA) dissolved in dichloromethane, which have a βHRS value approximately 17 × 10−30 cm4 statvolt −1 [35]. The studied samples present a small conjugated molecular

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structure, as one can check in Fig. 1. Consequently, the βHRS is expected to be close to the value of the PNA molecule. The theory for second-order nonlinear effects indicates that centrosymmetric molecular structures should not present second-order nonlinear optical effects [36, 37]. The molecular structures (molecular orbitals) have shown that both 4DBDBA and 4-DCDBA have a high-level of symmetry of the molecular structure (charge distribution), consequently, it is excepted a weak HRS signal. On the other hand, previous

experimental and theoretical studies have reported that HRS signal can be observed in centrosymmetric structures [38, 39]. Indeed, the HRS signal observed (Fig. 2) correspond to the values of the 25 × 10−30 cm4 statvolt −1 and 27 × 10−30 cm4 statvolt −1 for 4DBDBA and 4-DCDBA respectively, which are in the same order of magnitude of the

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N

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PNA.

Figure 2. Experimental first hyperpolarizability scattering signals for PNA (squares), 4-DBDBA

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(circles) and 4-DCDBA (triangles) as a function of the pump intensity. The solid lines represent the second order polynomial fits. The inset shows the linear dependence between HRS signal and the

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molecules concentrations. The solid lines represent the linear fits.

The results of the QCC for the static (βHRS(0;0,0)) and dynamic (βHRS(-2ω;ω,ω))

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first molecular hyperpolarizability of DBA derivatives in gas-phase and solvent environment are displayed in Table 1. For both compounds the theoretical values obtained evidence the effect of the solvent in the first molecular hyperpolarizability, revealing an increase of approximately 100% for static and 60% for dynamic hyperpolarizability. A good agreement between theoretical and experimental results for dynamic first molecular

hyperpolarizability is observed, by taken into account of the experimental error (20%) in HRS measurement. In Vacuum

In Dichloromethane

𝛽(0; 0,0) 𝛽(−2𝜔; 𝜔, 𝜔) 𝛽(0; 0,0) 𝛽(−2𝜔; 𝜔, 𝜔)

4-DBDBA

4

21

9

4-DCDBA

4

17

7

Experimental 𝛽(−2𝜔; 𝜔, 𝜔)

34

25 ± 5

26

27 ± 5

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Molecule

Table 1. Theoretical values obtained for the static and dynamic first-order hyperpolarizabilities of the DBA derivatives. 𝛽 is given in 10−30 cm4 statvolt −1 and 𝜆𝜔 = 1064 nm.

For 2PA measurements, the samples were dissolved in dichloromethane at a concentration of about 1019 molecules/cm3. It was excited with a femtosecond laser pulsed

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tuned from 470 to 790 nm, providing the 2PA experimental spectra. The experimental Zscan signatures corresponding to the maximum of 2PA band, from both molecular

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structures, are presented in Fig. S8 and S9 of the Supplementary material. The 2PA spectra

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of 4-DBDBA and 4-DCDBA are also presented in Fig. 3, showing a σ2PA maximum value

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of 24 GM at 620 nm and 17 GM at 600 nm, respectively. It is worth mentioning that the TPA peak was located close to the higher energy peak of the Gaussian decomposition for After this spectral region, a decrease of σ2PA is evident, however

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each compound.

approximately at 690 nm this decrease ends, showing a σ2PA value of about 7 GM.

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A previous work [21] have reported experimental 2PA coefficients values recorded at a fixed wavelength of 532 nm, obtained by a nanosecond pulsed laser, for the

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same family of dibenzylideneacetone molecules, which is two orders of magnitude larger than the reported in our study. These overestimation in 2PA coefficients values obtained

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from nanosecond pulses were observed in other molecules [40, 41]. Such difference of values is probably related to the long duration of nanosecond pulses that could trigger an

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excited state absorption, masking the pure electronic effect. In fact, the results obtained in this work are in the same order of magnitude obtained from organic compounds with similar conjugated length, such as chalcones derivatives [24], dibenzoylmethane [39] and emissive oxazole dyes [42] measured with femtosecond pulses.

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M

A

N

a)

b)

Figure 3 – a) 4-DBDBA, b) 4-DCDBA. 1PA experimental (black solid lines), decomposition of the 1PA

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experimental spectra (dashed and dotted lines) and 2PA experimental (symbols) spectra of DBA derivatives. The red solid lines represent the theoretical fitting obtained with SOS approach.

To further interpretation, we assign the observed one- and two-photon absorption, bands to the, QCC results. The first five of the fifteen calculated excited states (Table S3 of

Supplementary material) are presented in Table 2, as well the transition energy of decomposed experimental 1PA bands. The molecular orbitals (MO) obtained from the QCC are presented in Fig. 4 for the three first excited states (S1, S2 and S3). Generally, electronic transitions from non-bonding orbital (n) to antibonding π-orbital (π*), i.e. n-π* transition, are forbidden, resulting in a small molar absorption coefficient (ε=101~103 Mcm-1) whereas transitions from bonding π-orbital (π) to π*-orbital, i.e. π-π* transition, are

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1

strongly allowed (ε =104~105 M-1cm-1) [43]. One can check that the calculated S0 →S1

transition presents n-π* character because the MO on oxygen atom of HOMO-4 has no node on the molecular plane (n-orbital), while S0→S2 and S0→S3 transitions are π-π*. Two

decomposed peaks of observed 1PA-spectrum have ε in the order of 104 M-1cm-1 and the transition energies are close to those of the calculated results, consequently it is reasonable

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to assign them to the π-π* transitions regarding S2 and S3. On the other hand, the tail of the

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1PA spectra at the wavelength longer than 400 nm has ε less than 103 M-1cm-1 and can be

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assigned to the n-π* transition to S1.

The two π-π* excited states, S2 and S3, can be respectively assigned to lower and

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higher energy peaks of the decomposed 1PA spectrum by considering the symmetry of MOs involved. In the strict sense, the molecules are not centrosymmetric; nevertheless their

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π-orbitals have large extent of the centrosymmetric character and the discussion based on

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the (quasi)centrosymmetry is still useful. In this context, S2 consists of the HOMO-LUMO transition where HOMO is gerade, g (-like) and LUMO is ungerade, u (-like) MOs against

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the center of the molecule. Thus, S2 is g-u transition and has mostly 1PA-allowed and 2PAforbidden based on Laporte selection rule [44]. On the other hand, S3 is HOMO-1→LUMO

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transition where HOMO-1 is u (-like) MO and is mostly 1PA-forbidden and 2PA-allowed [43, 45]. This assignment can explain why the 2PA peak only overlap with the higher energy peak of the decomposed 1PA spectrum but does not with the lower energy one (Fig.

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3).

State 4-DBDBA

Experimental E [eV] (λ [nm])

Calculated E [eV] (λ [nm])

f

Orbital (contribution)

Transition nature

4-DCDBA S1 S2 S3 S4 S5

<3.18 (390) 3.67 (338) 4.12 (301)

3.48 (356.23) 3.65 (340.03) 4.14 (299.57) 4.79 (258.69) 4.79 (258.67)

0.0000 2.0224 0.1548 0.0236 0.0035

H-4→L (0.66535) H→L (0.66867) H-1→L (0.66403) H-2→L (0.48620) H-3→L (0.48691)

n-π* π-π* π-π*

<3.18 (390) 3.76 (329) 4.13 (300)

3.46 (357.92) 3.73 (332.32) 4.23 (293.45) 4.84 (256.27) 4.84 (256.26)

0.0000 1.9468 0.1385 0.0295 0.0057

H-2→L (0.67188) H→L (0.67370) H-1→L (0.67014) H-3→L (0.48738) H-4→L (0.48846)

n-π* π-π* π-π*

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S1 S2 S3 S4 S5

Table 2. Calculated energy levels (E) of the first 5 excited states, as well the oscillator strength (f) and the

orbital contribution and transition nature for 4-DBDBA and 4-DCDBA, by using TDA-DFT CAM-B3LYP/6-

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311+G(d,p).

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A

N

a)

b)

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Figure 4. Calculated molecular orbitals to the first three excited states (transition energy and oscillator

strength (f) are shown in parentheses) of the a) 4-DBDBA and b) 4-DCDBA in DCM medium. The u (-like)

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and g (-like) correspond the approximate symmetries, that is, ungerade- and gerade-like, respectively.

For further interpretation of the 2PA spectra, the sum-over-states (SOS) model was

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used to fit the experimental spectra (red lines in Fig. 3). In this work, only the contribution

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of the three-state can be relevant for the 2PA spectra (as it can be seen in Fig. S11 in

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Supplementary material), and the 2PA cross-section spectrum was explained by Eq. (4) for one intermediate state (k) and two destination states (f, f’) [46]: 2

2

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|𝜇0𝑘 |2 |𝜇𝑘𝑓′ | Γ0𝑓′ |𝜇0𝑘 |2 |𝜇𝑘𝑓 | Γ0𝑓 32 𝜋 3 𝐿4 𝑣2 [ ( + )] 2 2 2 2 2 5 (𝑐ℎ𝑛)2 (𝑣0𝑘 − 𝑣)2 + Γ0𝑘 (𝑣0𝑓 − 2𝑣) + Γ0𝑓 (𝑣0𝑓′ − 2𝑣) + Γ0𝑓 ′

(4)

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𝜎 2𝑃𝐴 (𝜈) =

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in which ν is the frequency of the laser, 𝑐 is the speed of light, ℎ is the Planck constant and 3𝑛2

L is the Onsager local field factor (𝐿 = 2𝑛2 +1, in which 𝑛 = 1.424 for dichloromethane).

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The spectroscopic parameters, 𝜈𝑖𝑗 , 𝛤𝑖𝑗 and 𝜇𝑖𝑗 , correspond to transition frequency, damping constant and transition dipole moments, respectively, of 𝑖 → 𝑗 transition (𝑖 = 0, 𝑘 and 𝑗 =

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𝑘, 𝑓, 𝑓 ′ ). Most of the parameters in Eq. (4) were obtained from 1PA spectra, such as the transitions frequency and damping constants. In addition, the transition dipole moment (𝜇0𝑘 ) between the ground and the k excited state can be estimated from 1PA spectra using [47]

3 𝑐ℎ 1

𝜇0𝑘 = √8𝜋3

𝑁 𝜈0𝑘

∫ 𝛼(𝜈0𝑘 )𝑑𝜈,

(5)

in which, N is the number of molecules per cm3 and 𝛼 is the absorption coefficient in cm−1 . The transition dipole moments between the excited states (𝜇𝑘𝑓 , 𝜇𝑘𝑓′ ) cannot be obtained

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directly from the experiments and were determined as adjustable parameters, retrieved by the SOS approach. Table 3 summarizes the spectroscopic parameters provided by the SOS fitting and by theoretical calculations.

4-DBDBA Exp.

Theo. (QCC) (k = S2, f = S3, f’ = S6)

6.80

12.09

𝝁𝒌𝒇 (D)

6.47

11.93

𝝁𝒌𝒇′ (D)

4.29

𝝂𝟎𝒌 (×1014 Hz)

8.63

𝝂𝒌𝒇 (×1014 Hz)

9.77

𝝂𝒌𝒇′ (×10 Hz)

12.55

𝚪𝟎𝒌 (×1013 Hz)

6.11

𝚪𝟎𝒇 (×1013 Hz)

11.73

6.90

11.00

8.27

2.38

8.74

8.82

8.98

9.02

10.03

9.80

10.23

13.08

12.79

13.32

6.11i

7.45

7.45 i

6.66

6.11 i

9.40

7.45 i

7.29

6.11 i

4.06

7.45 i

EP

𝚪𝟎𝒇′ (×1013 Hz)

(k = S2, f = S3, f’ = S8)

7.19

A

D

TE

14

Theo. (QCC)

M

𝝁𝟎𝒌 (D)

Exp.

N

parameters

4-DCDBA

U

SOS

Table 3: Spectroscopic parameters obtained through the SOS fitting of the experimental 2PA spectra (labeled “Exp.” values) and by quantum chemical calculations (labeled “Theo.(QCC)” values).

i

Taken from the

CC

experimental value of Γ0k and applied to be the same for Γ0f and Γ0f’.

A

Both simulated 1PA and 2PA spectra, shown in Fig. 5, have predicted the

displacement of the peak positions of the one- and two-photon absorption, which is also detected in the experimental spectra in agreement with selection rules due to the centrosymmetric-like molecular structures of the studied samples as discussed above. On this simulation, one can see that the lowest 2PA band presents a shoulder located at approximately 610 nm. These spectra are similar to the ones measured experimentally with

the Z-Scan technique. It indicates that S3 is more allowed for 2PA than S2. Also, the opposite behavior is observed on the 1PA simulated spectra, which agree very well with the

U

SC RI PT

1PA and 2PA experimental results.

c)

EP

TE

D

M

A

N

a)

b)

d)

CC

Figure 5. Experimental and simulated one-photon absorption (black solid line and blue dashed line) of a) 4DBDBA and c) 4-DCDBA compounds. In b) and d) the red dashed line represents simulated two-photon

A

absorption while the symbols represent 2PA experimental for 4-DBDBA and 4-DCDBA, respectively.

5. CONCLUSIONS In summary, we investigated, theoretically and experimentally, the second- and third-order nonlinear optical properties of two DBA derivatives. Employing the HRS technique, the experimental βHRS values obtained were 25 × 10−30 and 27 × 10−30 cm4 statvolt −1 for 4-DBDBA and 4-DCDBA respectively. The 2PA experimental

spectra we recorded using Z-scan technique. The maxima σ2PA values measured were 24 GM for 4-DBDBA and 17 GM for 4-DCDBA. Theoretical results obtained by QCC were carried out at TD-DFT theory level using the Gaussian 09 program package; in particular the spectral behavior, presents a good agreement with experimental results. In addition, it was observed an opposite behavior on the amplitudes of the transitions to S2 and S3 excited

SC RI PT

states between the 2PA and 1PA spectra. Both experimental and theoretical results showed that the g-u (-like) transition (S2) most allowed for 1PA was less allowed for 2PA and vice

versa u-u (-like) transition (S3). This behavior is supported by the selection rules, which are

related with the centrosymmetric-like nature of the studied compounds. In fact, the calculated MO have shown that HOMO-1, HOMO and LUMO have a high level of charge distribution symmetry, which suggests that the addition of distinct lateral substituents,

A

N

nonlinear optical response of this type of compounds.

U

increasing the charge asymmetry distribution, would contribute to the optimization of the

M

Acknowledgments

D

Financial support from FAPESP (Fundacao de Amparo a Pesquisa do Estado de Sao

TE

Paulo —, 2011/23587-1, 2016/20886-1), CNPQ (Conselho Nacional de Desenvolvimento Cientifico e Tecnologico), CAPES (Coordenacao de Aperfeicoamento de Pessoal de Nivel

EP

Superior) and the Air Force Office of Scientific Research (FA9550-12-1-0028 and FA9550-15-1-0521) are acknowledged. This work was performed in the framework of the

CC

National Institute of Photonics (INCT de Fotonica), Grant Number 465763/2014-

A

6,MCTI/CNPq/FACEPE.

References Castet, F.d.r., et al., Design and characterization of molecular nonlinear optical switches. Accounts of chemical research, 2013. 46(11): p. 2656-2665.

2.

Ekbote, A., et al., Structural, third-order optical nonlinearities and figures of merit of (E)-1-(3-substituted phenyl)-3-(4-fluorophenyl) prop-2-en-1-one under CW regime: new chalcone derivatives for optical limiting applications. Dyes and Pigments, 2017. 139: p. 720-729.

3.

Xing, J.-F., M.-L. Zheng, and X.-M. Duan, Two-photon polymerization microfabrication of hydrogels: an advanced 3D printing technology for tissue engineering and drug delivery. Chemical Society Reviews, 2015. 44(15): p. 50315039.

4.

Liu, Y., et al., A series of triphenylamine-based two-photon absorbing materials with AIE property for biological imaging. Journal of Materials Chemistry B, 2014. 2(33): p. 5430-5440.

5.

Polyzos, I., et al., Two-photon absorption properties of novel organic materials for three-dimensional optical memories. Chemical Physics Letters, 2003. 369(3): p. 264-268.

6.

Garcia, G., et al., Carbohydrate-conjugated porphyrin dimers: Synthesis and photobiological evaluation for a potential application in one-photon and twophoton photodynamic therapy. Bioorganic & medicinal chemistry, 2013. 21(1): p. 153-165.

7.

Hales, J.M., et al., Design of organic chromophores for all-optical signal processing applications. Chemistry of Materials, 2013. 26(1): p. 549-560.

8.

Tang, X., et al., Enhanced microscopic nonlinear optical properties of novel Y-type chromophores with dual electron donor groups. Chemical Physics Letters, 2016. 648: p. 114-118.

CC

EP

TE

D

M

A

N

U

SC RI PT

1.

A

9.

Frenette, M., et al., Nonlinear optical properties of multipyrrole dyes. Chemical physics letters, 2014. 608: p. 303-307.

10.

Kamada, K., et al., Cationic two-photon absorption chromophores with double-and triple-bond cores in symmetric/asymmetric arrangements. The Journal of Physical Chemistry C, 2009. 113(27): p. 11469-11474.

11.

Albota, M., et al., Design of organic molecules with large two-photon absorption cross sections. Science, 1998. 281(5383): p. 1653-1656.

Tan, J., et al., Small molecules of chalcone derivatives with high two-photon absorption activities in the near-IR region. Journal of Materials Chemistry C, 2016. 4(15): p. 3256-3267.

13.

Suzuki, N., et al., Near infrared two-photon-excited and-emissive dyes based on a strapped excited-state intramolecular proton-transfer (ESIPT) scaffold. Chemical science, 2018. 9(10): p. 2666-2673.

14.

Gendron, T., E. Davioud-Charvet, and T.J. Müller, Versatile Synthesis of Dissymmetric Diarylideneacetones via a Palladium-Catalyzed Coupling– Isomerization Reaction. Synthesis, 2012. 44(24): p. 3829-3835.

15.

Aher, R.B., et al., Dibenzylideneacetone analogues as novel Plasmodium falciparum inhibitors. Bioorganic & medicinal chemistry letters, 2011. 21(10): p. 3034-3036.

16.

Cao, B., et al., Synthesis of the pyridinyl analogues of dibenzylideneacetone (pyrdba) via an improved Claisen–Schmidt condensation, displaying diverse biological activities as curcumin analogues. Organic & biomolecular chemistry, 2012. 10(6): p. 1239-1245.

17.

Sedighi, V., P. Azerang, and S. Sardari, Antimycobacterial evaluation of novel [4, 5‐dihydro‐1H‐pyrazole‐1‐carbonyl] pyridine derivatives synthesized by microwave‐mediated Michael addition. Drug testing and analysis, 2015. 7(6): p. 550-554.

18.

Lee, H.-E., et al., Inhibition of specificity protein 1 by dibenzylideneacetone, a curcumin analogue, induces apoptosis in mucoepidermoid carcinomas and tumor xenografts through Bim and truncated Bid. Oral oncology, 2014. 50(3): p. 189-195.

19.

Periasamy, R., et al., Spectral investigation and structural characterization of dibenzalacetone: β-Cyclodextrin inclusion complex. Journal of Molecular Structure, 2014. 1068: p. 155-163.

CC

EP

TE

D

M

A

N

U

SC RI PT

12.

A

20.

Kiran, A.J., et al., χ (3) measurements and optical limiting in dibenzylideneacetone and its derivatives. Chemical physics, 2006. 324(2): p. 699-704.

21.

Reddy, N.S.K., et al., Synthesis, characterization and nonlinear optical properties of symmetrically substituted dibenzylideneacetone derivatives. Chemical Physics Letters, 2014. 616: p. 142-147.

22.

Kiran, A.J., et al., Substituent dependence of third-order optical nonlinearity in chalcone derivatives. Japanese Journal of Applied Physics, 2008. 47(8R): p. 6312.

Rajashekar, B., et al., Synthesis, characterization and two-photon absorption based broadband optical limiting in diarylideneacetone derivative. Journal of Photochemistry and Photobiology A: Chemistry, 2012. 238: p. 20-23.

24.

Abegão, L.M., et al., Second-and third-order nonlinear optical properties of unsubstituted and mono-substituted chalcones. Chemical Physics Letters, 2016. 648: p. 91-96.

25.

Clays, K. and A. Persoons, Hyper-Rayleigh scattering in solution. Physical review letters, 1991. 66(23): p. 2980.

26.

Hendrickx, E., K. Clays, and A. Persoons, Hyper-Rayleigh scattering in isotropic solution. Accounts of Chemical Research, 1998. 31(10): p. 675-683.

27.

Bersohn, R., Y.H. Pao, and H. Frisch, Double‐Quantum Light Scattering by Molecules. The Journal of Chemical Physics, 1966. 45(9): p. 3184-3198.

28.

Verbiest, T., K. Clays, and V. Rodriguez, Second-order nonlinear optical characterization techniques: an introduction. 2009: CRC press.

29.

Brasselet, S. and J. Zyss, Multipolar molecules and multipolar fields: probing and controlling the tensorial nature of nonlinear molecular media. JOSA B, 1998. 15(1): p. 257-288.

30.

Cyvin, S., J. Rauch, and J. Decius, Theory of Hyper‐Raman Effects (Nonlinear Inelastic Light Scattering): Selection Rules and Depolarization Ratios for the Second‐Order Polarizability. The Journal of Chemical Physics, 1965. 43(11): p. 4083-4095.

31.

Sheik-Bahae, M., et al., Sensitive measurement of optical nonlinearities using a single beam. IEEE journal of quantum electronics, 1990. 26(4): p. 760-769.

32.

Frisch, M., et al., Gaussian 09, revision D. 01. 2009, Gaussian, Inc., Wallingford CT.

A

CC

EP

TE

D

M

A

N

U

SC RI PT

23.

33.

Hirata, S. and M. Head-Gordon, Time-dependent density functional theory within the Tamm–Dancoff approximation. Chemical Physics Letters, 1999. 314(3): p. 291299.

34.

Ohta, K., et al., Two-photon absorption properties of two-dimensional π-conjugated chromophores: combined experimental and theoretical study. The Journal of Physical Chemistry A, 2010. 115(2): p. 105-117.

Woodford, J., M. Pauley, and C. Wang, Solvent dependence of the first molecular hyperpolarizability of p-nitroaniline revisited. The Journal of Physical Chemistry A, 1997. 101(11): p. 1989-1992.

36.

de la Torre, G., T. Torres, and F. Agulló‐López, The phthalocyanine approach to second harmonic generation. Advanced Materials, 1997. 9(3): p. 265-269.

37.

Liu, X., et al., Molecular Structures and Second-Order Nonlinear Optical Properties of Ionic Organic Crystal Materials. Crystals, 2016. 6(12): p. 158.

38.

Yaliraki, S. and R. Silbey, Hyper-Rayleigh scattering of centrosymmetric molecules in solution. The Journal of chemical physics, 1999. 111(4): p. 1561-1568.

39.

Dwivedi, Y., et al., Nonlinear optical characterizations of dibenzoylmethane in solution. Optics Communications, 2013. 293: p. 119-124.

40.

Swiatkiewicz, J., P. Prasad, and B. Reinhardt, Probing two-photon excitation dynamics using ultrafast laser pulses. Optics communications, 1998. 157(1): p. 135-138.

41.

Kim, O.-K., et al., New class of two-photon-absorbing chromophores based on dithienothiophene. Chemistry of materials, 2000. 12(2): p. 284-286.

42.

Abegão, L.M., et al., Oxazole Dyes With Potential For Photoluminescence Bioprobes: A Two-Photon Absorption Study. The Journal of Physical Chemistry C, 2018. 122(19): p. 10526-10534.

43.

Balzani, V., P. Ceroni, and A. Juris, Photochemistry and photophysics: concepts, research, applications. 2014: John Wiley & Sons.

44.

Purc, A., et al., Strategy towards large two-photon absorption cross-sections for diketopyrrolopyrroles. Journal of Materials Chemistry C, 2015. 3(4): p. 742-749.

CC

EP

TE

D

M

A

N

U

SC RI PT

35.

A

45.

46.

Kamada, K., et al., Two-photon absorption properties of symmetric substituted diacetylene: drastic enhancement of the cross section near the one-photon absorption peak. Chemical Physics Letters, 2003. 372(3): p. 386-393. Vivas, M.G., et al., Experimental and theoretical study on the one-and two-photon absorption properties of novel organic molecules based on phenylacetylene and azoaromatic moieties. The Journal of Physical Chemistry B, 2012. 116(50): p. 14677-14688.

Day, P.N., K.A. Nguyen, and R. Pachter, TDDFT Study of One-and Two-Photon Absorption Properties: Donor− π− Acceptor Chromophores. The Journal of Physical Chemistry B, 2005. 109(5): p. 1803-1814.

A

CC

EP

TE

D

M

A

N

U

SC RI PT

47.