Second-order Polarizability of Y-type Triphenylamine Chromophores

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 pi-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 beta(0) were obtained as 40 x10(-30) esu for BBtVPA, 64 x10(-30) esu for BBtBPA, and 238x10(-30) esu for BCfBPA, respectively, by solvatochromic method based on the two-level model, while 0.9-2.8 times enhancement of beta(0) were observed compared with the dipolar chromophores. Besides, extension of pi-conjugation and improvement of electron acceptor strength both increase the beta value. Quantum chemical calculations were carried out to aid in better understanding of the structure-property relationship.