溶致变色法测定类杂芪染料盐在纯固态时的分子一阶超极化率

詹传郎 王夺元^**
（中国科学院化学研究所 分子中心 光化学开放实验室 北京 100101）

摘要 本文建立了一个简单的测定类杂芪染料盐在纯固态时的分子一阶超极化率的实验方法。利用此方法，测得反式-(4-N,N-二甲胺基)-(4-N-甲基吡啶基)杂芪碘(DAPSI)、反式-(2-N-甲基吡咯基)-(4-N-甲基吡啶基)杂芪碘(MPPSI)、反式-(2-吡咯基)-(4-N-甲基吡啶基)杂芪碘(PPSI)、反式-(2-呋喃基)-(4-N-甲基吡啶基)杂芪碘(FPSI)、反式-(2-噻吩基)-(4-N-甲基吡啶基)杂芪碘(TPSI)和反式-(4-N-甲基吡啶基)杂芪碘(PSI)在纯固态时的分子一阶超极化率分别为 -46.1、-7.0、-5.4、-3.1和-2.2×10^-27 esu.
关键词 类杂芪染料 分子一阶超极化率 溶致变色法 溶剂效应
Abstract A simple experimental method for determining the first-order hyperpolarizabilities of five stilbazolium-like dyes in pure solid state has been developed by using solvatochromism according to the hypothesis of the equal energy levels both in pure solid state and in some solution systems. The five dyes are trans-(4-N,N-dimethylamino)-(4-N-methylpyridinio)-stilbazolium Iodide (DAPSI), trans-(N-methyl pyrrol-2-yl)-4-(N-methyl-pyridinio)-stilbazolium Iodide (MPPSI), trans-(pyrrol-2-yl)-4-(N-methyl-pyridinio)-stilbazoliumIodide(PPSI), trans-(furan-2-yl)-4-(N-methyl-pyridinio)-stilbazolium Iodide (FPSI), and trans-(thiophene-2-yl)-4-(N-methyl-pyridinio)-stilbazolium Iodide (TPSI). 
Keywords stilbazolium-like dye, hyperpolarizability, solvatochromism, solvent effect

Molecular First-Order Hyperpolarizabilities of Five Stilbazolium-Like Dyse in Pure Solid State Determined by Using Solvatochromism

Chuan-Langzhan   Duo-Yuanwang^**
(Laboratory of photochemistry, center of molecular science, Institute of Chemistry, The Chinese Academy of Sciences, Beijing 100101 )

Usually the dc-electric field induced second-harmonic generation (EFISH), Hyper-Rayleigh scattering (HRS) and solvatochromism are used to determine the first-order hyperpolarizabilities (b_ccc), in which all of the techniques are working in the solutions, so the results must involve the solvent effects. Kodaria^[1] , Clays^[2] and Woodford^[3] et al have considered some factors to characterize the levels of solvent effects on b_ccc, but their results are not giving the b_ccc values of the sample itself free of the solvent effects. We have reported that stilbazolium-like dyes are of large b_ccc, and observed the great influence of solvents on the b_ccc values^[4]. In this paper, we report a simple experimental method for determining the first-order hyperpolarizabilities of six stilbazolium-like dyes in pure solid state by using Solvatochromism, from which the b_ccc of stilbazolium-like dyes in pure solid are obtained, according to the hypothesis of the equal energy levels both in pure solid state and in some solution systems. 

The b_ccc of DAPSI、MPPSI、PPSI、FPSI and TPSI in fifteen solvents have been obtained by using solvatochromism⁽⁴⁾, the linear correlation between the b_ccc of DAPSI and solvent polarity, E_T^N is shown in Fig. 1 , from which the following equation can be obtained: b_ccc = K_i1 + K_i2 E_T^N  (×10^-27esu)             

Fig.1  The correlation between the bccc of DAPSI

We can see that the line 1, which contains chloroform, acetone, DMSO, DMF and acetonitrile, and line 2, which contains dichloromethane, 1,2-dichloroethane and 2-butanone are of very good linear relationship and the solvent polarity (E_T^N)， with  the correlation coefficients g₁ = 0.989 and g₂ = 0.966, respectively. Their intercepts, slopes and standard deviations are K₁₁ = -86.34, K₂₁ = 123.05, K₁₂ = -2297.83, K₂₂ = 6877.78, SD₁ =1.73, SD₂ = 27.08, respectively. The figure shows that the lines 1 and 2 intersect at D (E_T^N= 0.327, b_ccc= -46.1×10^-27esu. What is the physical meaning of the intersection D  Let us assume that the transition energy from the ground state S₀ to the excited singlet state S₁ in solid state is equal to that in a solution, if the molecules (DAPSI) become a condensed state including the solid or liquid and solutions from gas phase. The transition energies in solutions are effected by the polarity of solvent, E_T^N. The interactions of the solute molecules with the surrounding solvent molecules in the ground state is stronger than that in the excited singlet state, which induces the hyperchromic shift of the absorption bands and enhances the transition energy, while a reverse case of the interactions between the solutes and the solvents induces a bathochromic shift and drops the transition energy, and according this, it is possible to search for a solvating system, in which the transition energy from S₀ to S₁ of the solute molecule is equal to that of the solute molecule itself in the pure solid state. And similarly we also assume that there must be a solvent which effects on the level of polarizability of the electrons, or the charge transfer (CT) of DAPSI is equal to that effected by the same molecules of DAPSI around itself in solid state. Such a solvent should be correspond to the solvent which is response for the D point in Fig.1. So the ordinate of D point, which is the b_ccc in the corresponding solvent should be equal to that in pure solid state, therefore we define b_ccc^s = -46.1×10^-27esu for characterizing the first-order hyperpolarizability of DAPSI in pure solid state. It is very close to the value (-47.2×10^-27esu)  calculated from MOPAC by Bruce et al^[5].

Similar linear correlations between the b_ccc in nine solvents (including 4-methyl-pyridine) and the E_T^N for MPPSI, PPSI, FPSI and TPSI, respectively, are also evolved, from which the same equations, intersections and eight lines which are named as line 3 and 4 for MPPSI, 5 and 6 for PPSI, 7 and 8 for FPSI, 9 and 10 for TPSI, can be also obtained. Their relative linear correlation coefficients(g), intercepts (K_i1 ), slopes (K_i2 ) (i is the line number) and the first-order molecular hyperpolarizability for four dyes in pure solid state (b_ccc^s) are calculated and listed in Table 1.

Refenrences
[1] Kodoria T, Watanabe A, Ito O, et al. J. Chem. Soc., Faraday Trans., 1997, 93(17): 3039-3044.
[2] Clays K, Persoons A. Phys. Rev. Lett., 1991, 66: 2980-2983.
[3] Woodford J N, Pauley M A, Wang C H. J. Phys.Chem., A, 1997,101(11): 1989-1992.
[4] Zhan Chuan-Lang，Wang Duo-Yuan.  Sinica Phys. Chem.（in press）
[5] Bruce D W, Venning R G, Grayson M, et al. Adv. Mater. Opt. Electron. 1994, 4(4): 293-301.

Acknowledgement The project supported by NSFC (No. 29682001 and 29832030)