Dipartimento di Chimica Inorganica, Metallorganica e Analitica Lamberto Malatesta dell'Università degli Studi di Milano and Unità di Ricerca di Milano dell'INSTM, Via G. Venezian, 21-20133 Milano, Italy.
Chemphyschem. 2010 Feb 1;11(2):495-507. doi: 10.1002/cphc.200900696.
A series of 4-X-1-methylpyridinium cationic nonlinear optical (NLO) chromophores (X = (E)-CH=CHC(6)H(5); (E)-CH=CHC(6)H(4)-4'-C(CH(3))(3); (E)-CH=CHC(6)H(4)-4'-N(CH(3))(2); (E)-CH=CHC(6)H(4)-4'-N(C(4)H(9))(2); (E,E)-(CH=CH)(2)C(6)H(4)-4'-N(CH(3))(2)) with various organic (CF(3)SO(3)(-), p-CH(3)C(6)H(4)SO(3)(-)), inorganic (I(-), ClO(4)(-), SCN(-), Hg(2)I(6)) and organometallic (cis-Ir(CO)(2)I(2)) counter anions are studied with the aim of investigating the role of ion pairing and of ionic dissociation or aggregation of ion pairs in controlling their second-order NLO response in anhydrous chloroform solution. The combined use of electronic absorption spectra, conductimetric measurements and pulsed field gradient spin echo (PGSE) NMR experiments show that the second-order NLO response, investigated by the electric-field-induced second harmonic generation (EFISH) technique, of the salts of the cationic NLO chromophores strongly depends upon the nature of the counter anion and concentration. The ion pairs are the major species at concentration around 10(-3) M, and their dipole moments were determined. Generally, below 5x10(-4) M, ion pairs start to dissociate into ions with parallel increase of the second-order NLO response, due to the increased concentration of purely cationic NLO chromophores with improved NLO response. At concentration higher than 10(-3) M, some multipolar aggregates, probably of H type, are formed, with parallel slight decrease of the second-order NLO response. Ion pairing is dependent upon the nature of the counter anion and on the electronic structure of the cationic NLO chromophore. It is very strong for the thiocyanate anion in particular and, albeit to a lesser extent, for the sulfonated anions. The latter show increased tendency to self-aggregate.
一系列的 4-X-1-甲基吡啶阳离子非线性光学（NLO）发色团（X = （E）-CH=CHC（6）H（5）; （E）-CH=CHC（6）H（4）-4'-C（CH（3））（3）; （E）-CH=CHC（6）H（4）-4'-N（CH（3））（2）; （E）-CH=CHC（6）H（4）-4'-N（C（4）H（9））（2）; （E，E）-（CH=CH）（2）C（6）H（4）-4'-N（CH（3））（2））与各种有机（CF3SO3（-），p-CH3C6H4SO3（-）），无机（I（-），ClO4（-），SCN（-），[Hg2I6]（2-））和有机金属（cis-[Ir（CO）（2）I2]（-））抗衡阴离子进行了研究，目的是研究离子对的作用以及抗衡阴离子的离解或聚合对控制它们在无水氯仿溶液中的二阶 NLO 响应的影响。电子吸收光谱，电导率测量和脉冲场梯度自旋回波（PGSE）NMR 实验的组合使用表明，通过电场诱导二次谐波产生（EFISH）技术研究的阳离子 NLO 发色团的盐的二阶 NLO 响应强烈取决于抗衡阴离子的性质和浓度。在大约 10（-3）M 的浓度下，离子对是主要物种，并且测定了它们的偶极矩。通常，在低于 5x10（-4）M 时，由于具有改善的 NLO 响应的纯阳离子 NLO 发色团的浓度增加，离子对开始离解为离子，同时二阶 NLO 响应平行增加。在高于 10（-3）M 的浓度下，形成了一些多极聚集体，可能是 H 型，同时二阶 NLO 响应略有平行下降。离子对取决于抗衡阴离子的性质和阳离子 NLO 发色团的电子结构。对于特别是硫氰酸根阴离子，它非常强，并且对于磺化阴离子也是如此，尽管程度较小。后者显示出自聚集的增加趋势。
