Synthesis and characterization of new benzo[e]indol salts for second-order nonlinear optics

Organic second-order nonlinear optical materials are of great significance in the field of integrated photonics, optical data storage and optical information processing. In this work, two iodide salts with benzo[e]indol cations as electron-withdrawing groups were designed and synthesized, which are (E)-2-(4-hydroxy-3-methoxystyryl)-1,1,3-trimethyl-1H-benzo[e]indol-3-ium iodide (1-TB) and (E)-2-(3,4-dihydroxystyryl)-1,1,3-trimethyl-1H-benzo[e]indol-3-ium iodide (2-TB). Under the irradiation of 1064 nm laser, the second harmonic generations of the 1-TB and 2-TB powders are 760 and 580 times that of urea, respectively. Among them, crystals of 1-TB are successfully grown by a slow cooling method without using seed crystals. Bulk crystal with a size of 8.0 × 3.0 × 1.0 mm³ and many submillimeter single crystals with excellent optical quality are obtained.