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Synthesis, characterization, crystal structure and DFT studies on 1′,3′-dihydrospiro[fluorene-9,2′-perimidine]
Spectrochimica Acta Part A 82 (2011) 56–62
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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Synthesis, characterization, crystal structure and DFT studies on 1 ,3 -dihydrospiro[fluorene-9,2 -perimidine] Zhuomin Li, Wenli Deng ∗ College of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, PR China
a r t i c l e
i n f o
Article history: Received 31 October 2010 Received in revised form 18 June 2011 Accepted 23 June 2011 Keywords: Synthesis Crystal structure Vibrational frequency Electronic absorption spectra DFT
a b s t r a c t The title compound, 1 ,3 -dihydrospiro[fluorene-9,2 -perimidine] has been synthesized and characterized by NMR, ESI-MS, IR, elemental analysis, UV–vis and fluorescence spectroscopy. The crystal structures of the title compound and its co-crsytal with 9-fluorenone have also been determined by X-ray single crystal diffraction. Density functional theory (DFT) calculations and vibrational frequencies have been performed at B3LYP/6-31G* level. The comparisons between the experimental vibrational frequencies and the predicted data show that B3LYP/6-31G* method can simulate the IR of the title compound on the whole. The theoretical electronic absorption spectra have been calculated by using TD-DFT method and compared with the experimental result. The solid-fluorescence determination of the title compound reveals two emission bans at 430 and 590 nm while its co-crystal reveals only one emission band at 590 nm. © 2011 Elsevier B.V. All rights reserved.
1. Introduction During the past twenty years, organic light-emitting diodes (OLEDs) have received much attention owing to their promising display applications. However, one of the main drawbacks of OLED technology is the shorter lifetime of blue emitting materials compared to the green and red materials. Therefore, materials with stable blue emission within an electroluminescent device continue to hold the attention of number of research groups [1]. Oligofluorenes (OF) and polyfluorenes (PF) have been recognized as potential blue light-emitting materials because of their good charge transport properties, high luminescence efficiency, and excellent processibility [2–11]. Many groups reported the synthesis and properties of molecular systems having fluorene unit, such as spirofluorenes [12–17], terfluorenes [18–20], oligofluorenes [21,22], and polyfluorenes [23–25]. The electronic and photophysical properties exhibited by these systems have made them important in organic light-emitting diodes [26–30], organic field effect transistors [31,32], organic photovoltaic cells [9,33] and organic nonlinear optical applications [34,35]. Perimidines are of interest because they constitute an important class of natural and non-natural products, many of which exhibit useful biological activity [36]. Recently, it was found that the dihydroperimidine system was very effective as aromatic
∗ Corresponding author. E-mail address: [email protected] (W. Deng). 1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2011.06.061
electron donor groups [37]. In this work, we are motivated to introduce the dihydroperimidine group to the 9 position of fluorene which could form the spiro structrue. Herein, we report the facile synthesis on the title compound of 1 ,3 -dihydrospiro[fluorene9,2 -perimidine]. The crystal structures of the title compound and its co-crsytal with 9-fluorenone have also been determined by X-ray single crystal diffraction. Density functional theory (DFT) calculational results are obtained and compared with the experimental ones. 2. Experimental details 2.1. Physical measurements Melting points were recorded with a BÜCHI B-500 melting point apparatus and uncorrected. 1 H NMR and 13 C NMR spectra were obtained on a Bruker AVANCE Digital 400 spectrometer. MS measurements were performed on a Bruker Esquire HCT PLUS spectrometer. Elemental analyses for carbon, hydrogen and nitrogen were carried out on an Elementar Vario EL elemental analyzer. IR spectra (4000–500 cm−1 ), as KBr pellets, were recorded on a SP2000 FT-IR spectrophotometer (Pye Unicam Ltd., England). Electronic absorption spectra were recorded on a HITACHI 3010 UV–vis spectrophotometer and solid state fluorescence spectra were measured on a F96-fluorospectrophotometer. Thermal gravimetric analysis was carried out on a TA Instruments DTG60 TGA. A heating rate of 10 ◦ C min−1 under flowing N2 was used with runs being conducted from room temperature 25 ◦ C to high temperature 700 ◦ C.
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Table 1 Crystal data and structure refinement.
Scheme 1. Synthetic route of compound 1.
2.2. Synthesis of 1 ,3 -dihydrospiro [fluorene-9,2 -perimidine] (1) All chemicals were obtained from a commercial source and used without further purification. The synthetic route is shown in Scheme 1. To an oven dried 100 ml three necked round bottom flask, 9fluorenone (1.8 g, 10 mmol) and naphthalane-1,8-diamine (1.58 g, 10 mmol) were dissolved in ethanol (40 ml). Then a few drops of acetic acid were added. The reaction mixture was heated with refluxing for 24 h. After then, the mixture was cool to room temperature and was filtrated to produce a brown solid. The crude product was purified by recrystallization with a mixture of chloroform/hexane (1:1/v:v) (yield: 65%). Single crystals of 1 suitable for X-ray diffraction were grown by solvent evaporation of chloroform solution for a few days. MP: 255–256 ◦ C. 1 H NMR (400 MHz, CDCl3 , TMS): ı 4.25 (br s, 2H), 6.43–6.48 (m, 2H), 7.13 (t, J = 7.2 Hz, 2H), 7.24–7.29 (m, 6H), 7.36 (t, J = 7.2 Hz, 2H), 7.62 (d, J = 7.6 Hz, 2H). 13 C NMR (100 MHz, CDCl3 , TMS): ı 107.02, 112.82, 117.85, 119.92, 123.93, 127.25, 128.56, 129.81, 134.35, 138.90, 140.14. ESIMS (M+ ): 320. Elemental analysis calculated (%): C 86.22, H 5.03, N 8.74; found: C 86.15, H 4.96, N 8.89.
Crystal
1
2
CCDC No. Color/shape Chemical formula Formula weight Temperature (K) Crystal system Space group Unit cell dimension a (Å) b (Å) c (Å) ˛ (◦ ) ˇ (◦ ) (◦ ) Volume (Å3 ) Z Density (calculated) (g/cm3 ) Absorption coefficient (mm−1 ) Diffractometer/scan
768329 Brown/block C23 H16 N2 320.38 173(2) Orthorhombic Pbca
768330 Red/block C36 H24 N2 O 500.57 173(2) Orthorhombic Pca2(1)
14.914(9) 16.2126(8) 26.4850(14) 90 90 90 6404(4) 16 1.329 0.078 Bruker AXS SMART 1000 CCD diffractometer 2.01–27.07 32,682 7013 (Rint = 0.0353)/4771 [I > 2(I)] 4349/0/345 1.047 R1 = 0.0513, wR2 = 0.1371 R1 = 0.0826, wR2 = 0.1612
18.0732(9) 7.7216(4) 17.8262(9) 90 90 90 2487.7(2) 4 1.337 0.081 Bruker AXS SMART 1000 CCD diffractometer 2.25–27.04 12,502 2800 (Rint = 0.0266)/2436 [I > 2(I)] 2800/1/352 1.170 R1 = 0.0386, wR2 = 0.0967 R1 = 0.0482, wR2 = 0.1026
range for data collection (◦ ) Reflections measured Independent/observed reflections
Data/restraints/parameters Goodness of fit on F2 Final R indices [I > 2(I)] R indices (all data)
2.3. Synthesis of co-crystal (2) The purified compound 1 (1.6 g, 5 mmol) and fluorenone (0.9 g, 5 mmol) were dissolved in ethanol and stirred at room temperature for 1 h. The undissolved solids were removed by filtration. The resulting solution was set aside to evaporate slowly. After a few days, red crystals (0.9 g) of 2 suitable for X-ray diffraction were obtained. Elemental analysis found (%): C 86.52, H 4.63, N 5.68, which is consistent with the calculated result (C 86.38, H 4.83, N 5.60). 2.4. Crystal structure determination X-ray crystallographic data were collected with a Bruker AXS SMART CCD diffractometer, using graphite-monochromated Mo ˚ The data were collected at 173 K K␣ radiation ( = 0.71073 A). and the structure was resolved by direct methods and refined by full-matrix least-squares on F2 . The computation was performed with the SHELXL-97 program [38]. All non-hydrogen atoms were anisotropically refined. The hydrogen atoms were located by difference synthesis and refined isotropically. The key crystallographic data are given in Table 1. CCDC-768329 for compound 1 and CCDC-768330 for co-crsytal 2 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre (CCDC), 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336 33; email: [email protected]. 3. Computational methods DFT calculations with a hybrid functional B3LYP (Becke’s three parameter hybrid functional using the LYP correlation functional) at basis set 6-31G* by the Berny method [39] were performed
Fig. 1. Molecular structure of compound 1 with the atomic numbering scheme.
with the Gaussian 03 software package [40]. Vibrational frequencies calculated ascertain the structure was stable (no imaginary frequencies). Time-dependent density functional theory (TD-DFT) [41–43] calculations of electronic absorption spectra were performed on the optimized structure.
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Fig. 2. A view of the crystal packing down the b axis for compound 1. H atoms have been omitted for clarity.
4. Results and discussion 4.1. Description for the crystal structures of 1 and 2 For compound 1, the displacement ellipsoid plot with the numbering scheme is shown in Fig. 1. Fig. 2 shows a perspective view of the crystal packing in the unit cell. Selected bond lengths and bond angles by X-ray diffractions are listed in Table 2 along with the calculated bond parameters. The molecular structure of compound 1 consists of 1,3dihydroperimidine group bonded to the fluorenyl group at the 9 position. All of the bond lengths and bond angles in the fluorenyl ring and naphthyl ring are in the normal range. All the C–N bond lengths are also in the normal range. The fluorenyl ring (C(1)–C(13)) defines a plane P1, with the biggest deviation being 0.030 A˚ for C(9) atom. The C(1), N(14) and N(25) atoms define a plane P2. The naphthyl ring (C(15)–C(24)) defines a plane P3, with the biggest deviation being 0.028 A˚ for C(15) atom. The dihedral angles between the P1–P2, P1–P3 and P2–P3 are 89.95(2)◦ , 86.77(2)◦ and 35.52(2)◦ , respectively. It means that the naphthalene moiety and the fluorene moiety are nearly orthogonal. The two -systems interconnect via a sp3 -hybridized atom C(1). In the crystal lattice, there are weak X–H. . . supramolecular interactions. The perpendicular arrangement of the molecule leads to a high steric demand of the resulting rigid structure, efficiently suppressing molecular interactions between the -systems [4]. It has been demonstrated that fluorenone derivatives are excellent model compounds for the investigation of the intramolecular
and intermolecular hydrogen bonding interactions [44–46]. As shown in Fig. 3, co-crystal 2 consists of two independent molecules of 1 and fluorenone. It has been reported that the molecular structure of fluorenone is planar in single crystalline phase [47], which agree with the current results of that existed in the co-crystalline phase. Additionally, due to its rigid structure, the configuration of molecule 1 is almost the same within the single crystalline or cocrystalline phase. It can be seen from Fig. 3 that molecules 1 and fluorenone recognize each other through the formation of a strong ˚ N. . .O: N–H. . .O C intermolecular hydrogen bond (O. . .H: 2.15 A; ˚ N–H. . .O: 146◦ ). Weak – interactions were observed 2.92 A; between the fluorenone molecule and the fluorene moiety in molecule 1. The interplanar distance, intercentroid distance, and ˚ respecthe displacement of the two rings are 3.68, 4.28 and 2.18 A, tively. As shown in Fig. 4, there are weak – interactions between the asymmetric units leading to the formation of -stacks that run parallel to the b-axis. Therefore, the co-crystal is stabilized by – and hydrogen bonded supramolecular interactions. 4.2. Optimized geometry The optimized geometry of compound 1 has been obtained at B3LYP/6-31G* level. Some optimized geometric parameters are also
Table 2 Selected structural parameters by X-ray and theoretical calculations.
Bond lengths (Å) C(1)–N(14) C(1)–N(25) N(14)–C(15) C(23)–N(25) C(1)–C(2) C(1)–C(13) C(7)–C(8) Bond angles (◦ ) C(2)–C(1)–C(13) C(2)–C(1)–N(14) C(13)–C(1)–N(14) C(2)–C(1)–N(25) C(13)–C(1)–N(25) C(1)–N(14)–C(15) C(1)–N(25)–C(23)
Experimental
Calculated
1.464(2) 1.459(2) 1.392(2) 1.392(2) 1.521(3) 1.535(3) 1.467(3)
1.467 1.467 1.396 1.396 1.528 1.546 1.474
101.49(16) 109.86(15) 113.37(15) 110.58(15) 114.39(16) 118.52(15) 119.58(15)
101.38 110.13 114.35 110.13 114.34 119.00 118.97
Fig. 3. Molecular structure of co-crystal 2.
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Table 3 Comparison of the observed and calculated vibrational spectra of compound 1. Assignments
Experimental IR (with KBr)
Calculated (B3LYP/6-31G*)
N–H str. Phenyl ring C–H str. C–N str. Phenyl ring C–C str. Phenyl ring C–H ip. def. Phenyl ring C–H ip. def. Phenyl ring C–H ip. def. Phenyl ring C–H ip. def. Phenyl ring C–H ip. def. N–H ip. def. Phenyl ring C–H ip. def. Phenyl ring C–H ip. def. Phenyl ring C–H ip. def. Phenyl ring C–H ip. def. Phenyl ring C–H opp. def. Phenyl ring C–H opp. def. Phenyl ring C–H opp. def. Phenyl ring C–H opp. def. Phenyl ring C–H opp. def. N–H opp. def. N–H opp. def. N–H opp. def. N–H opp. def.
3367 3037 1623 1598 1489 1448 1409 1380 1314 1278 1203 1165 1107 1070 929 838 811 761 733 661 640 601 544
3429 3091–3048 1611 1584 1478 1437 1393 1358 1305 1261 1180 1122 1093 1055 907 828 791 749 740 649 628 599 540
str, stretch; def, deform; ip, in plane; opp, out of plane.
the vibrational frequencies for the system studied here on the whole. 4.4. Electronic absorption spectra Fig. 4. A view of the crystal packing down the b axis for co-crystal 2. H atoms have been omitted for clarity.
listed in Table 2. Comparing the theoretical values with the experimental one indicates that all of the optimized bond lengths are slightly larger than the experimental values, as the theoretical calculations are performed for isolated a molecule in gaseous phase and the experimental results are for a molecule in solid state. The geometry of the solid-state structure is subject to intermolecular forces, such as van der Waals interactions and crystal packing forces [48]. The biggest differences of the bond lengths and bond angles between experimental and the predicted values are −0.009 A˚ for C(1)–C(13) bond distance and −0.98◦ for C(13)–C(1)–C(14) bond angle, which suggests that the calculation result is satisfactory and the B3LYP/6-31G* level of theory is suitable for the system studied here.
For compound 1, the UV–vis absorption spectra have been measured in dichloromethane solution at room temperature. To compare the experimental spectra with theoretical values, TD-DFT method has been applied to predict UV–vis spectra based on the B3LYP/6-31G* level optimized structure. Both the experimental and predicted UV–vis spectra are shown in Fig. 6. The theoretical UV–vis spectra are drawn using the SWizard program, revision 4.6 [51,52]. The detailed experimental and theoretical UV–vis spectra values are listed in Table 4. As shown in Fig. 6, in experiment, there exist three peaks at 268, 310 and 352 nm, respectively. In theory, there are four peaks at 270, 307, 358, and 398 nm for gas phase. Therefore, TD-DFT-B3LYP/6-31G* level can approximately simulate the experimental electronic spectra for this system. In view of calculated absorption spectra, the maximum absorption wavelength corresponds to the electronic transition from the highest occupied
4.3. Vibrational frequency The experimental IR spectra and the simulated IR spectra of compound 1 are shown in Fig. 5, where the calculated intensity is plotted against the harmonic vibrational frequencies. Vibrational frequencies calculated at B3LYP/6-31G* level were scaled by 0.96 [49], which is a typical scaled factor for the calculated method. Some primary calculated harmonic frequencies are listed in Table 3 and compared with the experimental data. The descriptions concerning the assignment have also been indicated in Table 3. Gauss-view program [50] was used to assign the calculated harmonic frequencies. As shown in Fig. 5, the predicted harmonic vibrational frequencies and the experimental data are very similar to each other except for the peak at 3367 cm−1 in experimental IR spectra, which is attributed to the influence to the unavoidable vO–H peak of water (broad peak at 3400 cm−1 ) in our experiment. In a word, the scaled frequencies of the DFT calculation are close to the corresponding FTIR vibration data and the DFT-B3LYP/6-31G* level can predicted
Fig. 5. Experimental IR spectra and predicted spectrum at B3LYP/6-31G* level of compound 1.
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Fig. 6. Experimental (dash line) and theoretical (solid line) electronic spectra of compound 1.
molecular orbital (HOMO) to lowest unoccupied molecular orbital (LUMO) with 99% contribution. The other wavelength, oscillator strength and calculated counterparts with major contributions can be seen in Table 4. It is well known that both the HOMO and LUMO are the main orbital taking part in chemical reaction. The HOMO energy characterizes the ability of electron giving, LUMO energy characterizes the ability of electron accepting, and the gap between HOMO and LUMO characterizes the molecular chemical stability [53,54]. Surfaces for the frontier orbitals were drawn to understand the bonding scheme of the present compound. Herein, two important molecular orbitals (MO) were examined for compound 1: the highest occupied MO and the lowest unoccupied MO can be seen in Fig. 7. The positive phase is red and the negative one is green. The HOMO presents a charge density localized on the naphthalene ring, but LUMO is characterized by a charge distribution on the fluorenyl residue, which indicates that the 9-substituted perimidine group can greatly influence the electronic transition.
Fig. 7. Isodensity surfaces of frontier molecular orbital for compound 1.
processes of the compounds. The thermal decomposition temperatures (5% weight loss) of 1 and 2 observed were about 340 ◦ C, 235 ◦ C, respectively (Fig. 9b). The residues of compound 1 and 2 at 600 ◦ C could be carbon formed at high temperature. Generally, these results demonstrated that both the compounds are thermally stable.
4.5. Fluorescence spectra Experimental solid-state fluorescence spectra of compound 1 and 2 are shown in Fig. 8. Both the spectra have the peak at 590 nm. It is distinct that compound 1 exhibit one more band around 430 nm, which may be attributed to the existence of the N–H. . .O C hydrogen bonds that increase the intermolecular charge transfer (ICT) and quench the fluorescence in the solid state [46]. 4.6. Thermal analysis The thermal properties of compound 1 and co-crystal 2 were investigated by thermogravimetric analysis (TGA). As shown in Fig. 9a, compound 1 has a sharp peak at 256 ◦ C while co-crsytal 2 has the peak at 160.8 ◦ C. Both peaks can be assigned to the melting
Fig. 8. Solid-state fluorescence spectra of compound 1 (solid line) and co-crystal 2 (dash line).
Table 4 Experimental and theoretical UV–vis values. Exp. Wavelength (nm) 268
310 352
Calc. (TD-DFT) log ε 1.12
0.65 1.25
Wavelength (nm) 270
307 358 398
Oscillator strength 0.1864
0.1037 0.0989 0.0267
Electronic transition modes HOMO-2 → LUMO (41%) HOMO-2 → LUMO+1 (28%) HOMO-4 → LUMO (22%) HOMO → LUMO+2 (94%) HOMO → LUMO+1 (97%) HOMO → LUMO (99%)
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Fig. 9. (a) DSC plots and (b) TG plots of compounds 1 and 2.
5. Conclusion Spiro[1,3-dihydroperimidine-2,9 -fluorene] and its co-crsytal with 9-fluoreone have been synthesized and characterized by NMR, ESI-MS, IR, elemental analysis, and UV–vis. The crystal structure determinations show that compound 1 and its co-crystal 2 crystallizes in orthorhombic, space group Pbca and Pca2(1). DFT-B3LYP/6-31G* method can simulate the crystal structure and vibrational spectra of compound 1 on the whole. The TD-DFT method at B3LYP/6-31G* level can be used to predict the electronic spectra approximately. The solid-fluorescence spectra suggest that the intermolecular hydrogen bond could quench the fluorescence of compound 1. Both of the compounds show moderate thermal stability in nitrogen. Acknowledgments This work was supported financially by the National Natural Science Foundation of China (No. 51073059 and No. 91023002), State Key Development Program for Basic Research of China (No. 2009CB930604) and Cooperation Project in Industry, Education and Research of Guangdong Province and Ministry of Education of China (No. 2010B090400123). References [1] K. Müllen, U. Scherf, Organic Light-Emitting Devices: Synthesis, Properties and Applications , Wiley-VCH, Weinheim, 2006.
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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Synthesis, characterization, crystal structure and DFT studies on 1 ,3 -dihydrospiro[fluorene-9,2 -perimidine] Zhuomin Li, Wenli Deng ∗ College of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, PR China
a r t i c l e
i n f o
Article history: Received 31 October 2010 Received in revised form 18 June 2011 Accepted 23 June 2011 Keywords: Synthesis Crystal structure Vibrational frequency Electronic absorption spectra DFT
a b s t r a c t The title compound, 1 ,3 -dihydrospiro[fluorene-9,2 -perimidine] has been synthesized and characterized by NMR, ESI-MS, IR, elemental analysis, UV–vis and fluorescence spectroscopy. The crystal structures of the title compound and its co-crsytal with 9-fluorenone have also been determined by X-ray single crystal diffraction. Density functional theory (DFT) calculations and vibrational frequencies have been performed at B3LYP/6-31G* level. The comparisons between the experimental vibrational frequencies and the predicted data show that B3LYP/6-31G* method can simulate the IR of the title compound on the whole. The theoretical electronic absorption spectra have been calculated by using TD-DFT method and compared with the experimental result. The solid-fluorescence determination of the title compound reveals two emission bans at 430 and 590 nm while its co-crystal reveals only one emission band at 590 nm. © 2011 Elsevier B.V. All rights reserved.
1. Introduction During the past twenty years, organic light-emitting diodes (OLEDs) have received much attention owing to their promising display applications. However, one of the main drawbacks of OLED technology is the shorter lifetime of blue emitting materials compared to the green and red materials. Therefore, materials with stable blue emission within an electroluminescent device continue to hold the attention of number of research groups [1]. Oligofluorenes (OF) and polyfluorenes (PF) have been recognized as potential blue light-emitting materials because of their good charge transport properties, high luminescence efficiency, and excellent processibility [2–11]. Many groups reported the synthesis and properties of molecular systems having fluorene unit, such as spirofluorenes [12–17], terfluorenes [18–20], oligofluorenes [21,22], and polyfluorenes [23–25]. The electronic and photophysical properties exhibited by these systems have made them important in organic light-emitting diodes [26–30], organic field effect transistors [31,32], organic photovoltaic cells [9,33] and organic nonlinear optical applications [34,35]. Perimidines are of interest because they constitute an important class of natural and non-natural products, many of which exhibit useful biological activity [36]. Recently, it was found that the dihydroperimidine system was very effective as aromatic
∗ Corresponding author. E-mail address: [email protected] (W. Deng). 1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2011.06.061
electron donor groups [37]. In this work, we are motivated to introduce the dihydroperimidine group to the 9 position of fluorene which could form the spiro structrue. Herein, we report the facile synthesis on the title compound of 1 ,3 -dihydrospiro[fluorene9,2 -perimidine]. The crystal structures of the title compound and its co-crsytal with 9-fluorenone have also been determined by X-ray single crystal diffraction. Density functional theory (DFT) calculational results are obtained and compared with the experimental ones. 2. Experimental details 2.1. Physical measurements Melting points were recorded with a BÜCHI B-500 melting point apparatus and uncorrected. 1 H NMR and 13 C NMR spectra were obtained on a Bruker AVANCE Digital 400 spectrometer. MS measurements were performed on a Bruker Esquire HCT PLUS spectrometer. Elemental analyses for carbon, hydrogen and nitrogen were carried out on an Elementar Vario EL elemental analyzer. IR spectra (4000–500 cm−1 ), as KBr pellets, were recorded on a SP2000 FT-IR spectrophotometer (Pye Unicam Ltd., England). Electronic absorption spectra were recorded on a HITACHI 3010 UV–vis spectrophotometer and solid state fluorescence spectra were measured on a F96-fluorospectrophotometer. Thermal gravimetric analysis was carried out on a TA Instruments DTG60 TGA. A heating rate of 10 ◦ C min−1 under flowing N2 was used with runs being conducted from room temperature 25 ◦ C to high temperature 700 ◦ C.
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Table 1 Crystal data and structure refinement.
Scheme 1. Synthetic route of compound 1.
2.2. Synthesis of 1 ,3 -dihydrospiro [fluorene-9,2 -perimidine] (1) All chemicals were obtained from a commercial source and used without further purification. The synthetic route is shown in Scheme 1. To an oven dried 100 ml three necked round bottom flask, 9fluorenone (1.8 g, 10 mmol) and naphthalane-1,8-diamine (1.58 g, 10 mmol) were dissolved in ethanol (40 ml). Then a few drops of acetic acid were added. The reaction mixture was heated with refluxing for 24 h. After then, the mixture was cool to room temperature and was filtrated to produce a brown solid. The crude product was purified by recrystallization with a mixture of chloroform/hexane (1:1/v:v) (yield: 65%). Single crystals of 1 suitable for X-ray diffraction were grown by solvent evaporation of chloroform solution for a few days. MP: 255–256 ◦ C. 1 H NMR (400 MHz, CDCl3 , TMS): ı 4.25 (br s, 2H), 6.43–6.48 (m, 2H), 7.13 (t, J = 7.2 Hz, 2H), 7.24–7.29 (m, 6H), 7.36 (t, J = 7.2 Hz, 2H), 7.62 (d, J = 7.6 Hz, 2H). 13 C NMR (100 MHz, CDCl3 , TMS): ı 107.02, 112.82, 117.85, 119.92, 123.93, 127.25, 128.56, 129.81, 134.35, 138.90, 140.14. ESIMS (M+ ): 320. Elemental analysis calculated (%): C 86.22, H 5.03, N 8.74; found: C 86.15, H 4.96, N 8.89.
Crystal
1
2
CCDC No. Color/shape Chemical formula Formula weight Temperature (K) Crystal system Space group Unit cell dimension a (Å) b (Å) c (Å) ˛ (◦ ) ˇ (◦ ) (◦ ) Volume (Å3 ) Z Density (calculated) (g/cm3 ) Absorption coefficient (mm−1 ) Diffractometer/scan
768329 Brown/block C23 H16 N2 320.38 173(2) Orthorhombic Pbca
768330 Red/block C36 H24 N2 O 500.57 173(2) Orthorhombic Pca2(1)
14.914(9) 16.2126(8) 26.4850(14) 90 90 90 6404(4) 16 1.329 0.078 Bruker AXS SMART 1000 CCD diffractometer 2.01–27.07 32,682 7013 (Rint = 0.0353)/4771 [I > 2(I)] 4349/0/345 1.047 R1 = 0.0513, wR2 = 0.1371 R1 = 0.0826, wR2 = 0.1612
18.0732(9) 7.7216(4) 17.8262(9) 90 90 90 2487.7(2) 4 1.337 0.081 Bruker AXS SMART 1000 CCD diffractometer 2.25–27.04 12,502 2800 (Rint = 0.0266)/2436 [I > 2(I)] 2800/1/352 1.170 R1 = 0.0386, wR2 = 0.0967 R1 = 0.0482, wR2 = 0.1026
range for data collection (◦ ) Reflections measured Independent/observed reflections
Data/restraints/parameters Goodness of fit on F2 Final R indices [I > 2(I)] R indices (all data)
2.3. Synthesis of co-crystal (2) The purified compound 1 (1.6 g, 5 mmol) and fluorenone (0.9 g, 5 mmol) were dissolved in ethanol and stirred at room temperature for 1 h. The undissolved solids were removed by filtration. The resulting solution was set aside to evaporate slowly. After a few days, red crystals (0.9 g) of 2 suitable for X-ray diffraction were obtained. Elemental analysis found (%): C 86.52, H 4.63, N 5.68, which is consistent with the calculated result (C 86.38, H 4.83, N 5.60). 2.4. Crystal structure determination X-ray crystallographic data were collected with a Bruker AXS SMART CCD diffractometer, using graphite-monochromated Mo ˚ The data were collected at 173 K K␣ radiation ( = 0.71073 A). and the structure was resolved by direct methods and refined by full-matrix least-squares on F2 . The computation was performed with the SHELXL-97 program [38]. All non-hydrogen atoms were anisotropically refined. The hydrogen atoms were located by difference synthesis and refined isotropically. The key crystallographic data are given in Table 1. CCDC-768329 for compound 1 and CCDC-768330 for co-crsytal 2 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre (CCDC), 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336 33; email: [email protected]. 3. Computational methods DFT calculations with a hybrid functional B3LYP (Becke’s three parameter hybrid functional using the LYP correlation functional) at basis set 6-31G* by the Berny method [39] were performed
Fig. 1. Molecular structure of compound 1 with the atomic numbering scheme.
with the Gaussian 03 software package [40]. Vibrational frequencies calculated ascertain the structure was stable (no imaginary frequencies). Time-dependent density functional theory (TD-DFT) [41–43] calculations of electronic absorption spectra were performed on the optimized structure.
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Fig. 2. A view of the crystal packing down the b axis for compound 1. H atoms have been omitted for clarity.
4. Results and discussion 4.1. Description for the crystal structures of 1 and 2 For compound 1, the displacement ellipsoid plot with the numbering scheme is shown in Fig. 1. Fig. 2 shows a perspective view of the crystal packing in the unit cell. Selected bond lengths and bond angles by X-ray diffractions are listed in Table 2 along with the calculated bond parameters. The molecular structure of compound 1 consists of 1,3dihydroperimidine group bonded to the fluorenyl group at the 9 position. All of the bond lengths and bond angles in the fluorenyl ring and naphthyl ring are in the normal range. All the C–N bond lengths are also in the normal range. The fluorenyl ring (C(1)–C(13)) defines a plane P1, with the biggest deviation being 0.030 A˚ for C(9) atom. The C(1), N(14) and N(25) atoms define a plane P2. The naphthyl ring (C(15)–C(24)) defines a plane P3, with the biggest deviation being 0.028 A˚ for C(15) atom. The dihedral angles between the P1–P2, P1–P3 and P2–P3 are 89.95(2)◦ , 86.77(2)◦ and 35.52(2)◦ , respectively. It means that the naphthalene moiety and the fluorene moiety are nearly orthogonal. The two -systems interconnect via a sp3 -hybridized atom C(1). In the crystal lattice, there are weak X–H. . . supramolecular interactions. The perpendicular arrangement of the molecule leads to a high steric demand of the resulting rigid structure, efficiently suppressing molecular interactions between the -systems [4]. It has been demonstrated that fluorenone derivatives are excellent model compounds for the investigation of the intramolecular
and intermolecular hydrogen bonding interactions [44–46]. As shown in Fig. 3, co-crystal 2 consists of two independent molecules of 1 and fluorenone. It has been reported that the molecular structure of fluorenone is planar in single crystalline phase [47], which agree with the current results of that existed in the co-crystalline phase. Additionally, due to its rigid structure, the configuration of molecule 1 is almost the same within the single crystalline or cocrystalline phase. It can be seen from Fig. 3 that molecules 1 and fluorenone recognize each other through the formation of a strong ˚ N. . .O: N–H. . .O C intermolecular hydrogen bond (O. . .H: 2.15 A; ˚ N–H. . .O: 146◦ ). Weak – interactions were observed 2.92 A; between the fluorenone molecule and the fluorene moiety in molecule 1. The interplanar distance, intercentroid distance, and ˚ respecthe displacement of the two rings are 3.68, 4.28 and 2.18 A, tively. As shown in Fig. 4, there are weak – interactions between the asymmetric units leading to the formation of -stacks that run parallel to the b-axis. Therefore, the co-crystal is stabilized by – and hydrogen bonded supramolecular interactions. 4.2. Optimized geometry The optimized geometry of compound 1 has been obtained at B3LYP/6-31G* level. Some optimized geometric parameters are also
Table 2 Selected structural parameters by X-ray and theoretical calculations.
Bond lengths (Å) C(1)–N(14) C(1)–N(25) N(14)–C(15) C(23)–N(25) C(1)–C(2) C(1)–C(13) C(7)–C(8) Bond angles (◦ ) C(2)–C(1)–C(13) C(2)–C(1)–N(14) C(13)–C(1)–N(14) C(2)–C(1)–N(25) C(13)–C(1)–N(25) C(1)–N(14)–C(15) C(1)–N(25)–C(23)
Experimental
Calculated
1.464(2) 1.459(2) 1.392(2) 1.392(2) 1.521(3) 1.535(3) 1.467(3)
1.467 1.467 1.396 1.396 1.528 1.546 1.474
101.49(16) 109.86(15) 113.37(15) 110.58(15) 114.39(16) 118.52(15) 119.58(15)
101.38 110.13 114.35 110.13 114.34 119.00 118.97
Fig. 3. Molecular structure of co-crystal 2.
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Table 3 Comparison of the observed and calculated vibrational spectra of compound 1. Assignments
Experimental IR (with KBr)
Calculated (B3LYP/6-31G*)
N–H str. Phenyl ring C–H str. C–N str. Phenyl ring C–C str. Phenyl ring C–H ip. def. Phenyl ring C–H ip. def. Phenyl ring C–H ip. def. Phenyl ring C–H ip. def. Phenyl ring C–H ip. def. N–H ip. def. Phenyl ring C–H ip. def. Phenyl ring C–H ip. def. Phenyl ring C–H ip. def. Phenyl ring C–H ip. def. Phenyl ring C–H opp. def. Phenyl ring C–H opp. def. Phenyl ring C–H opp. def. Phenyl ring C–H opp. def. Phenyl ring C–H opp. def. N–H opp. def. N–H opp. def. N–H opp. def. N–H opp. def.
3367 3037 1623 1598 1489 1448 1409 1380 1314 1278 1203 1165 1107 1070 929 838 811 761 733 661 640 601 544
3429 3091–3048 1611 1584 1478 1437 1393 1358 1305 1261 1180 1122 1093 1055 907 828 791 749 740 649 628 599 540
str, stretch; def, deform; ip, in plane; opp, out of plane.
the vibrational frequencies for the system studied here on the whole. 4.4. Electronic absorption spectra Fig. 4. A view of the crystal packing down the b axis for co-crystal 2. H atoms have been omitted for clarity.
listed in Table 2. Comparing the theoretical values with the experimental one indicates that all of the optimized bond lengths are slightly larger than the experimental values, as the theoretical calculations are performed for isolated a molecule in gaseous phase and the experimental results are for a molecule in solid state. The geometry of the solid-state structure is subject to intermolecular forces, such as van der Waals interactions and crystal packing forces [48]. The biggest differences of the bond lengths and bond angles between experimental and the predicted values are −0.009 A˚ for C(1)–C(13) bond distance and −0.98◦ for C(13)–C(1)–C(14) bond angle, which suggests that the calculation result is satisfactory and the B3LYP/6-31G* level of theory is suitable for the system studied here.
For compound 1, the UV–vis absorption spectra have been measured in dichloromethane solution at room temperature. To compare the experimental spectra with theoretical values, TD-DFT method has been applied to predict UV–vis spectra based on the B3LYP/6-31G* level optimized structure. Both the experimental and predicted UV–vis spectra are shown in Fig. 6. The theoretical UV–vis spectra are drawn using the SWizard program, revision 4.6 [51,52]. The detailed experimental and theoretical UV–vis spectra values are listed in Table 4. As shown in Fig. 6, in experiment, there exist three peaks at 268, 310 and 352 nm, respectively. In theory, there are four peaks at 270, 307, 358, and 398 nm for gas phase. Therefore, TD-DFT-B3LYP/6-31G* level can approximately simulate the experimental electronic spectra for this system. In view of calculated absorption spectra, the maximum absorption wavelength corresponds to the electronic transition from the highest occupied
4.3. Vibrational frequency The experimental IR spectra and the simulated IR spectra of compound 1 are shown in Fig. 5, where the calculated intensity is plotted against the harmonic vibrational frequencies. Vibrational frequencies calculated at B3LYP/6-31G* level were scaled by 0.96 [49], which is a typical scaled factor for the calculated method. Some primary calculated harmonic frequencies are listed in Table 3 and compared with the experimental data. The descriptions concerning the assignment have also been indicated in Table 3. Gauss-view program [50] was used to assign the calculated harmonic frequencies. As shown in Fig. 5, the predicted harmonic vibrational frequencies and the experimental data are very similar to each other except for the peak at 3367 cm−1 in experimental IR spectra, which is attributed to the influence to the unavoidable vO–H peak of water (broad peak at 3400 cm−1 ) in our experiment. In a word, the scaled frequencies of the DFT calculation are close to the corresponding FTIR vibration data and the DFT-B3LYP/6-31G* level can predicted
Fig. 5. Experimental IR spectra and predicted spectrum at B3LYP/6-31G* level of compound 1.
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Fig. 6. Experimental (dash line) and theoretical (solid line) electronic spectra of compound 1.
molecular orbital (HOMO) to lowest unoccupied molecular orbital (LUMO) with 99% contribution. The other wavelength, oscillator strength and calculated counterparts with major contributions can be seen in Table 4. It is well known that both the HOMO and LUMO are the main orbital taking part in chemical reaction. The HOMO energy characterizes the ability of electron giving, LUMO energy characterizes the ability of electron accepting, and the gap between HOMO and LUMO characterizes the molecular chemical stability [53,54]. Surfaces for the frontier orbitals were drawn to understand the bonding scheme of the present compound. Herein, two important molecular orbitals (MO) were examined for compound 1: the highest occupied MO and the lowest unoccupied MO can be seen in Fig. 7. The positive phase is red and the negative one is green. The HOMO presents a charge density localized on the naphthalene ring, but LUMO is characterized by a charge distribution on the fluorenyl residue, which indicates that the 9-substituted perimidine group can greatly influence the electronic transition.
Fig. 7. Isodensity surfaces of frontier molecular orbital for compound 1.
processes of the compounds. The thermal decomposition temperatures (5% weight loss) of 1 and 2 observed were about 340 ◦ C, 235 ◦ C, respectively (Fig. 9b). The residues of compound 1 and 2 at 600 ◦ C could be carbon formed at high temperature. Generally, these results demonstrated that both the compounds are thermally stable.
4.5. Fluorescence spectra Experimental solid-state fluorescence spectra of compound 1 and 2 are shown in Fig. 8. Both the spectra have the peak at 590 nm. It is distinct that compound 1 exhibit one more band around 430 nm, which may be attributed to the existence of the N–H. . .O C hydrogen bonds that increase the intermolecular charge transfer (ICT) and quench the fluorescence in the solid state [46]. 4.6. Thermal analysis The thermal properties of compound 1 and co-crystal 2 were investigated by thermogravimetric analysis (TGA). As shown in Fig. 9a, compound 1 has a sharp peak at 256 ◦ C while co-crsytal 2 has the peak at 160.8 ◦ C. Both peaks can be assigned to the melting
Fig. 8. Solid-state fluorescence spectra of compound 1 (solid line) and co-crystal 2 (dash line).
Table 4 Experimental and theoretical UV–vis values. Exp. Wavelength (nm) 268
310 352
Calc. (TD-DFT) log ε 1.12
0.65 1.25
Wavelength (nm) 270
307 358 398
Oscillator strength 0.1864
0.1037 0.0989 0.0267
Electronic transition modes HOMO-2 → LUMO (41%) HOMO-2 → LUMO+1 (28%) HOMO-4 → LUMO (22%) HOMO → LUMO+2 (94%) HOMO → LUMO+1 (97%) HOMO → LUMO (99%)
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Fig. 9. (a) DSC plots and (b) TG plots of compounds 1 and 2.
5. Conclusion Spiro[1,3-dihydroperimidine-2,9 -fluorene] and its co-crsytal with 9-fluoreone have been synthesized and characterized by NMR, ESI-MS, IR, elemental analysis, and UV–vis. The crystal structure determinations show that compound 1 and its co-crystal 2 crystallizes in orthorhombic, space group Pbca and Pca2(1). DFT-B3LYP/6-31G* method can simulate the crystal structure and vibrational spectra of compound 1 on the whole. The TD-DFT method at B3LYP/6-31G* level can be used to predict the electronic spectra approximately. The solid-fluorescence spectra suggest that the intermolecular hydrogen bond could quench the fluorescence of compound 1. Both of the compounds show moderate thermal stability in nitrogen. Acknowledgments This work was supported financially by the National Natural Science Foundation of China (No. 51073059 and No. 91023002), State Key Development Program for Basic Research of China (No. 2009CB930604) and Cooperation Project in Industry, Education and Research of Guangdong Province and Ministry of Education of China (No. 2010B090400123). References [1] K. Müllen, U. Scherf, Organic Light-Emitting Devices: Synthesis, Properties and Applications , Wiley-VCH, Weinheim, 2006.
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