Organic Salts Suppress Aggregation and Enhance the Hyperpolarizability of a π-Twisted Chromophore

Twisted intramolecular charge-transfer (TICT) chromophores exhibit extraordinary hyperpolarizabilities, beta, and are therefore promising for electro-optic technologies. Nevertheless, centrosymmetric aggregate formation severely diminishes beta in concentrated solutions or in polymer matrices. Herein, the remarkable effects of organic salts on the linear and nonlinear optical response of a high beta benzimidazolium-based TICT chromophore, B2TMC-2, are reported. Addition of Bu4P+Br- to B2TMC-2 solution in CHCl3 induces a halochromic blueshift, primarily reflecting interactions between Bu4P+Br- and the B2TMC-2 cationic portion. DC electric-field induced second-harmonic generation (EFISH) measurements on B2TMC-2+Bu4P+Br- solution reveal a large mu beta = -22,160 x 10(-48)esu, unprecedented for any chromophore with such a broad optical transparency window. Moreover, Bu4P+Br- is shown to suppress B2TMC-2 aggregation, thereby preserving high mu beta in concentrated solutions. This phenomenon should be applicable to many other NLO chromophores.