Abstract
High-performance bi-functional materials are in urgent demand for the next-generation integrated optical devices. In this work, we successfully synthesized the first tricyanomelaminate with bi-functional optical responses, namely Cs(3)C(6)N(9)•H(2)O (I), from its analogue Na(3)C(6)N(9)•3H(2)O by a facile ion exchange method. In contrast to Na(3)C(6)N(9)•3H(2)O, I realizes an optimal arrangement of π-conjugated (C(6)N(9))(3-) anion groups in its crystal structure. As a result, the second-order nonlinear optical (NLO) response is greatly enhanced from nearly zero of Na(3)C(6)N(9)•3H(2)O to ∼9.8 × KH(2)PO(4) of I. Furthermore, I exhibits a giant linear optical anisotropic response (i.e. birefringence) of 0.52 at the wavelength of 550 nm. Both responses are almost the largest among the inorganic compounds of π-conjugated rings, which indicates that I has great potential as a bi-functional optical crystal. Structural and theoretical analyses reveal the microscopic origin of excellent optical properties. This work would attract a lot of interest to the persistently neglected potential of tricyanomelaminates as linear optical and NLO crystals.