Facile bromine-termination of nonlinear optical chromophore: remarkable optimization in photophysical properties, surface morphology and electro-optic activity

This paper describes how a small molecular structure modification can enhance the microscopic and macroscopic properties of chromophore. A new chromophore WJ10 is synthesized by applying bromine-termination to the remote donor of WJ6, an existing donor-pi-acceptor chromophore. This small molecular change can significantly enhance the photophysical properties of chromophore and generate intriguing inverted solvatochromism in solutions. The absorption intensity of chromophore WJ10 in a guest-host electro-optic polymer film is 40-50% higher than that of the chromophore WJ6, which results in the increase of microscopic first-order hyperpolarizability of WJ10 in guest-host electro-optic (EO) polymer film. DFT calculations was carried out to explain this intriguing photophysical property in both solutions and in films. Bromine-termination also has the influence on macroscopic surface morphology of WJ10 in EO films, making WJ10 more homogeneously dispersed than WJ6. In EO activities, EO coefficient obtained with the WJ10 film is more than two times larger (211 pm V-1) than benchmark value 104 pm V-1 obtained from WJ6. The enhanced electro-optic activity with WJ10 is due to the enhancement of the microscopic hyperpolarizability and the better chromophore alignment in the poling process. This study demonstrates the structure-property relationship in bromine-termination of nonlinear optical chromophore, which can be further explored for the synthesis of new organic EO materials.