Comparative studies on structure–nonlinearity relationships in a series of novel second-order nonlinear optical chromophores with different aromatic amine donors

Abstract

A series of second-order nonlinear optical chromophores containing an identical π-bridge and electron acceptor but different, aromatic amine electron-donating groups have been synthesized and systematically investigated. The donors studied here include traditional donors carbazole, triphenylamine and N,N-diethylaniline and novel donor phenothiazine, phenoxazine and N-(4-methoxyphenyl)phenoxazine. The ultraviolet absorption, solvatochromic, redox properties, density functional theory calculations, thermal stabilities and electro-optic activities of these chromophores were systematically studied to compare the strength of the donors and illustrate the structure–performance relationships within six chromophores. The results show that the new donors have stronger electron-donating ability than traditional donors. Moreover, they show reduced energy gap, much larger molecular quadratic hyperpolarizability (μβ) and r33 value. Exemplified by the N-(4-methoxyphenyl)phenoxazine chromophore, it showed nearly three times higher μβ and more than four times higher r33 value than that of the N-hexylcarbazole containing chromophore.