LI Jing ZHOU Ping-Ping LIU Zhen LI Jing-To②

?

Crystal Structure, Photoluminescence, and TheoreticalStudies of Dihydropyran Derivatives①

LI JingaZHOU Ping-PingbLIU ZhenaLI Jiang-Taoa②

a(710065)b(071001)

Two novel dihydropyran compounds (1 and 2) containing a triphenylamine group were synthesized and characterized. The structure of compound 2 was verified by single-crystal X-ray crystallography. It crystallizes in triclinic, space groupwith= 6.9943(4),= 8.1360(4),= 23.9274(14) ?,= 87.692(4),= 88.940(5),= 85.223(4)o,= 1355.62(13) ?3,= 2,(000) = 520,D= 1.199 Mg/m3,M= 489.24 and= 0.075 mm?1. The UV-vis absorption and fluorescence of the two compounds were discussed. The two compounds exhibited strong blue emissions under ultraviolet light excitation. The molecular structure and HOMO and LUMO levels of compound 2 were calculated by density functional theory (DFT) at the B3LYP/6-31G(d) level.

dihydropyran, crystallography, UV-vis, fluorescence, DFT;

1 INTRODUCTION

Dihydropyran is an important component of numerous synthetic and natural products with wide- range biological activities, including anticoagulant, insecticidal, anthelminthic, hypnotic, antifungal, phytoalexin, and HIV protease inhibition[1-3]. Consi- dering the importance of these compounds, the researchers focused on the synthesis of dihydropyran derivatives. On the other hand, the triphenylamine group, three aryl rings linked by a central nitrogen, are found to be effective photosensitive materials, and exhibit promising nonlinear optical properties[4, 5].Single-crystal X-ray diffraction, which can reveal the molecularconformation, intramolecular andintermolecular interactions in the solid state,is among the most versatile techniques used to study the dihydropyran derivatives.

In this work, we report the synthesis, crystal structure, photophysical properties and theoretical investigation of two novel dihydropyran compoundscontaining an triphenylamine group, namely, 2-amino- 4-[4-(di--tolyl-amino)-phenyl]-5-oxo-5,6,7,8-tetra-hydro-4-chromene-3-carbonitrile (1) and 2- amino-4-[4-(di--tolyl-amino)-phenyl]-7,7-dimethyl-5-oxo-5,6,7,8-tetrahydro-4-chromene-3-carboni-trile (2), as shown in Fig. 1.

2 EXPERIMENTAL

2. 1 Apparatus and materials

IR spectra (400～4000 cm-1) were measured on a Nicolet 380 spectrophotometer.1H NMR spectra were obtained using a Varian Inova 500 spectro- meter (at 500 MHz). Melting points were taken on a RY-1 micro melting apparatus; the thermometer was uncorrected. UV-vis absorption and emission spec- tra were recorded using a ThermoEvolution 300 spectrometer and a Cary Eclipse spectrometer, respectively. All the chemicals were commercially available and used without further purification. All the solvents were dried using standard methods before use.

Fig. 1 . Chemical structure of dihydropyran derivatives 1 and 2

2. 2 Synthesis and characterization of compounds 1 and 2

Dihydropyran derivatives (1 and 2)were synthe- sized according to a reported procedure[6]. A mix- ture of 3,5-cyclohexanedione (or 1,1-dimethyl-3,5- cyclohexanedione) (1.12 or 1.40 g, 10 mmol), 4-(di--tolyl-amino)-benzaldehyde (3.01 g, 10 mmol), malononitrile (0.66 g, 10 mmol) and 4-(dimethyl- amino)pyridine (DMAP, 0.12 g, 1 mmol) in ethanol (100mL) was refluxed for 5h and then cooled to room temperature. The precipitates were filtered and sequentially washed with ice-cooled water and ethanol and then dried under a vacuum.

2-Amino-4-[4-(di--tolyl-amino)-phenyl]-5-oxo-5,6,7,8-tetrahydro-4-chromene-3-carbonitrile (1): Yield (2.12 g, 46%) as yellow solid. m.p.: 232～233 ℃. IR (KBr pellet cm-1): 2186 (C≡N), 1681 (C=O), 1604 (C–O), 1498 (C=C) cm-1.1H NMR (DMSO-d,, ppm): 7.084～7.105 (d, 4H), 6.995～7.016 (d, 4H), 6.801～6.882 (q, 6H), 4.117 (s, 1H), 2.586～2.616 (t, 2H), 2.281～2.329 (m, 2H), 2.252 (s, 6H), 1.883～1.987 (m, 2H). HRMS (ESI+):/: calcd. for C30H27N3O2: 484.1995 [M+Na+]; found: 484.1932.

2-Amino-4-[4-(di--tolyl-amino)-phenyl]-7,7-di-methyl-5-oxo-5,6,7,8-tetrahydro-4-chromene-3-carbonitrile (2): Yield (2.59 g, 53%) as yellow solid. m.p.: 207～208 ℃. IR (KBr pellet cm-1): 2186 (C≡N), 1672 (C=O), 1604 (C–O), 1507 (C=C) cm-1.1H NMR (DMSO-d,, ppm): 7.077～7.097 (d, 4H), 6.977～6.999 (d, 4H), 6.855～6.875 (d, 4H), 6.796～6.818 (d, 2H), 4.106 (s, 1H), 2.497～2.506 (t, 4H), 2.246 (s, 6H), 1.037 (s, 3H), 0.963 (s, 3H). HRMS (ESI+):/: calcd. for C32H31N3O2: 512.2308 [M+Na+]; found: 512.2354.

2. 3 Crystal structure determination

A yellow crystal of compound 2 with approxi- mate dimensions of 0.20mm ×0.22mm×0.20mmwas selected and mounted on a glass fiber. Theintensity data were collected on a Bruker SmartAPEX CCD-based diffractometer equipped with agraphite-monochromator equipped with a Moradiation (=0.71073 ?) by using ascan mode at 293(2) K.The empirical absorption was applied to the intensitydata. A total of 8979 reflections were collected inthe range of 2.51<<25.00 (–8≤≤8, –9≤≤9, –28≤≤28), of which 4783 were independent (int= 0.0248) and 3434 were observed with> 2(). The intensity data were corrected for Lorentz and polarization effects as well as for empirical absorption based on the multi-scan technique. The structure wassolved by direct methods and refined by full-matrixleast-squares techniques on2with SHELX-97[7, 8]. All non-H atoms were refined with anisotropicdisplacement parameters. The hydrogen atoms werelocated theoretically and refined with riding modelposition parameters as well as fixed isotropicthermal parameters. The final= 0.0523,=0.1723 (= 1/[2(F2) + (0.1000)2+ 0.0000], where= (F2+ 2F2)/3), (Δ/)max= 0.000,= 1.019, (Δ)max=0.160 and (Δ)min= –0.190 e/?3.

2. 4 Quantum chemical calculations

The structure of compound 2 was optimized by density functional theory (DFT) using a B3LYP/6- 31G(d) basis set. The structure optimization and energy calculations were performed with the GAUS- SIAN 09 program.

3 RESULTS AND DISCUSSION

3. 1 Molecular structure

For compound 2, the crystal structure is given in Fig. 2; the selected bond lengths and bond angles are listed in Table 1. The newly formed pyran ring is essentially planar because the maximum devia- tion of the atoms in the skeleton from the C(1)– O(1)–C(6) plane is only 0.7347 ?. The adjacent ketone ring is also essentially planar because the C(8) atom makes a maximum deviation of 0.3602 ? from the C(5)–C(6)–C(7) plane. The torsional angle between the two planes is 13.646°. The benzene ring plane (C(14)–C(13)–C(18)) makes a 85.314° angle with the pyran ring plane, and the atom C(18) deviates from that pyran ring plane by 2.7452 ?.

Table 1. Experimental and Calculated Parameters of Selected Bond Lengths and Bond Angles of Compound 2

Fig. 2 . Crystal structure of compound 2

On the other hand, the three aryl rings of the triphenylamine moiety are not a coplanar structure. The central nitrogen and its adjacent three carbon atoms are basically coplanar, forming a quasi- equilateral trigonal NC3 plane, with the sum of the three C–N–C angles (358.85°) being very close to 360°. Around the central nitrogen, three phenyl ring planes are arranged in a propeller-like fashion.

3. 2 UV-vis absorption and fluorescence of dihydropyran derivatives 1 and 2

The UV-vis absorption and PL spectra of dihy- dropyran derivatives 1 and 2 in diluted dichloro- methane solutions are shown in Fig. 3. The absorp- tion spectral features of compounds 1 and 2 are quite similar because of their highly similar struc- tures, which mainly contain one triphenylamine donor group and one pyran acceptor group, respec- tively. Both compounds 1 and 2 have only one intense absorption peak each at 294 and 279 nm, respectively. Due to the weak electron-donating capability of dimethyl group in the structure of compound 2, the absorption peak is slightly blue- shifted compared with that of compound 1.

Fig. 3 also shows the PL spectra of compounds 1 and 2 in diluted dichloromethane solutions. Com- pound 2 exhibits a bright blue emission, with a maximum emission peak at 470 nm, which is blue-shifted by about 19 nm with respect to that of compound 1 at 489 nmbecause of the effect of dimethyl group in compound 2.

Fig. 3 . UV-vis absorption and emission spectra of compounds 1 and 2 in diluted dichloromethane solutions

3. 3 Quantum chemical calculations

B3LYP/6-31G(d) optimized geometrical data of compound 2 are in good agreement with the X-ray crystallographic data, as listed in Table 1. The average discrepancy of the selected bond lengths between theoretical and experimental data is less than ±0.02 ?, and that of the selected bond angles is lower than ±2°. Therefore, the results using density functional theory (DFT) at the B3LYP/6-31G(d) level are creditable.

The HOMO and LUMO levels of compound 2 were deduced using DFT method, as shown in Fig. 4, which is essential for deducing their S0and S1states. This knowledge is important for better under- standing of their fluorescence and nonlinear optical properties.

The HOMO and LUMO diagrams of compound 2 showed that the compound is likely to exhibit an efficient electron transfer from the triphenylamine group of HOMO to the pyran molecular skeleton of LUMO if electronic transitions occur. The HOMO for the compound is localized at the triphenylamine group, whereas the LUMO at the pyran moiety. Therefore, when electrons transfer from HOMO to LUMO, the electron density significantly decreases in the electron-donating triphenylamine system, accompanied by an increase in the electron density of the electron accepting pyran system. This indica- tes that the electrons transfer from the triphenyla- mine to the pyran group.

HOMO????????????????????LUMO

Based on the optimized structure, the HOMO and LUMO levels of compound 2 are –6.150 and –2.264 eV, respectively, and the energy gap between HOMO and LUMO is approximately 3.886 eV. A large HOMO-LUMO gap implies high kinetic stability and low chemical reactivity, given that adding electrons to a high-lying LUMO or extrac- ting them from a low-lying HOMO is energetically unfavorable[9].

(1) Bonsignore, L.; Loy, G.; Secci, D.; Calignano, A. Synthesis and pharmacological activityof 2-oxo-(2) 1-benzopyran-3-carboxamide derivatives.1993, 28, 517–520.

(2) Khan, A. T.; Lal, M.; Ali, S.; Khan, M. M. One-pot three-component reaction for the synthesis of pyran annulated heterocyclic compounds using DMAP as a catalyst.2011, 52, 5327–5332.

(3) Mochida, S.; Shimizu, M.; Hirano, K.; Satoh, T.; Miura, M. Synthesis of naphtho[1,8-]pyran derivatives and related compounds through hydroxy group directed C–H bond cleavage under rhodium catalysis.2010, 5, 847–851.

(4) Sun, Y. F.; Cui, Y. P. The synthesis, characterization and properties of coumarin-based chromophores containing a chalcone moiety.2008, 78, 65–76.

(5) Li, J.; Hou, Z.; Li, F.; Zhang, Z.; Zhou, Y.; Luo, X.; Li, M. Synthesis, photoluminescent, antibacterial activities and theoretical studies of 4-hydroxycoumarin derivatives.2014, 1075, 509–514.

(6) Eshghi, H.; Zohuri, G. H.; Sandaroos, R.; Damavandi, S. Synthesis of novel benzo[f]chromene compounds catalyzed by ionic liquid.2012, 18, 67–70.

(7) Sheldrick, G. M.. University of G?ttingen, Germany 1997.

(8) Sheldrick, G. M.. University of G?ttingen, Germany 1997.

(9) Zhang, H.; Yu, T. Z.; Zhao, Y. L.; Fan, D. W.; Xia, Y. J.; Zhang, P.; Qiu, Y. Q.; Chen, L. L. Synthesis, crystal structure and photoluminescence of 3-(4-(anthracen-10-yl)phenyl)-benzo[5,6]coumarin.2010, 75, 325–329.

28 September 2014; accepted19 December 2014 (CCDC 1027770 for compound 2)

①This work was supported by grants from the Industrial Research Project of Science and Technology Department of Shaanxi Province (No. 2013K09-25)

. E-mail: lijiangtao-968@xawl.edu.cn

10.14102/j.cnki.0254-5861.2011-0525