Second-order polarizability of Y-type triphenylamine chromophores

Abstract

Three Y-type triphenylamine chromophores, N,N-Bis-{4-[1-(2-benzothiazolyl)-1,3-butadiene-4-yl]phenyl} aniline (BBtBPA), N,N-bis-{4-[2-(2-benzothiazolyl)vinyl]phenyl} aniline (BBtVPA), and N,N-bis-{4-[1-(3-cyano-2-dicyanomethylidene-5,5- dimethyl-2,5-dihydro-4-furyl)-1,3-butadiene-4-yl]phenyl} aniline (BCfBPA) and four dipolar ones, 1-(2-benzothiazolyl)-4-[4-(N,N-diphenyl)amino]phenyl-1,3-butadiene (BtAPB), 4-[2-(2-benzothiazolyl)vinyl]-N,N-diphenylaniline (BtVPA), 1-[(3-cyano-2-dicyano methylidene-5,5-dimethyl-2, 5-dihydro)-4-furyl]-4-[4-(N,N-diphenyl)-amino]-phenyl-1,3-butadiene (CfAPB) and 4-[2-(3-cyano-2-dicyanomethylidene-5,5- dimethyl-2,5-dihydro-4-furyl)vinyl]-N,N-diphenylaniline (CfVPA) were synthesized through Knoevenagel reaction, with variations in the electron acceptor substitutes and π-conjugated bridges. Absorption and fluorescence properties of these chromophores were investigated. Maxima absorption in dichloromethane were at 425 nm for BBtVPA, 443 nm for BBtBPA, and 613 nm for BCfBPA, respectively. The fluorescence maxima of BBtVPA and BBtBPA were at 516 and 558 nm, respectively. Compared with their dipolar analogues, the Y-type chromophores present about 30 nm bathochromic-shift of absorption maxima, along with slightly bathochromic-shift of fluorescence maxima. Static second-order polarizabilities β 0 were obtained as 40×10 -30 esu for BBtVPA, 64×10 -30 esu for BBtBPA, and 238×10 -30 esu for BCfBPA, respectively, by solvatochromic method based on the two-level model, while 0.9-2.8 times enhancement of β 0 were observed compared with the dipolar chromophores. Besides, extension of π-conjugation and improvement of electron acceptor strength both increase the β value. Quantum chemical calculations were carried out to aid in better understanding of the structure-property relationship.

通过Knoevenagel反应合成了3个Y型三苯胺生色分子N,N-二{4-[2-(2-苯并噻唑基)乙烯基]苯基}苯胺(BBtVPA)、N,N-二{4-[1-(2-苯并噻唑基)-1,3-丁二烯-4-基]苯基}苯胺(BBtBPA)和N,N-二{4-[1-(2-二氰基甲叉-3-氰基-5,5-二甲基-2,5-二氢-4-呋喃基)-1,3-丁二烯-4-基]苯基}苯胺(BCfBPA), 以及4个一维偶极分子4-[2-(2-苯丙噻唑基)乙烯基]-N,N-二苯基苯胺(BtVPA)、1-(2-苯并噻唑基)-4-[4-(N,N-二苯基)氨基]苯基-1,3-丁二烯(BtAPB)、1-[(2-二氰基甲叉-3-氰基-5,5-二甲基-2,5-二氢)-4-呋喃基]-4-[4-(N,N-二苯基氨基)]苯基-1,3-丁二烯(CfAPB)和4-[2-(2-二氰基甲叉-3-氰基-5,5-二甲基-2,5-二氢呋喃-4-基)乙烯基]-N,N-二苯基苯胺(CfVPA). 测定了生色分子的紫外吸收和荧光性质, 在二氯甲烷中, Y型分子BBtVPA, BBtBPA和BCfBPA的最大吸收波长分别为425, 443和613 nm, 比偶极分子红移了约30 nm, Y型分子BBtVPA和BBtBPA的最大荧光发射峰分别位于516和558 nm, 比偶极分子稍有红移. 根据双能级模型理论, 用溶致变色法测定了生色分子的二阶非线性极化率(β), Y型分子BBtVPA, BBtBPA和BCfBPA的β0分别为40×10-30, 64×10-30和238×10-30 esu, 比相应的偶极分子分别提高了0.9~2.8倍. 结果表明, 提高吸电子基团强度, 增大共轭体系有助于获得更大的β值.