Synthesis and characterization of a new chalcone-based nonlinear optical crystal: BBC

Abstract

A new chalcone-based nonlinear optical crystal BBC (C22H17BrO2) using long π-conjugated and halogen substituent, as a potential alternative to develop organic crystals, are reported. BBC was designed and synthesized by replacing benzyloxy and -Br groups on both sides of molecular framework. Flaky yellowish BBC single crystal with size of 5 × 5 × 1 mm3 was grown by solution evaporation method. BBC crystal crystallizes in the monoclinic system, Pc (NO. 7) space group, with noncentrosymmetric structure. In the BBC molecule, benzyl oxide acts as donor (D) and Br and carbonyl group act as acceptor (A), forming D - π - A - π - A structure with electron gradient. The introduction of Br group, which contributes to strong halogen bond formation, lead to the “head-to-tail” arrangement. Remarkably, BBC exhibits strong second harmonic generation (SHG) intensity (14 × KDP and 2.2 × Urea), wide transmission range (600-1600 nm, >60%), high optical energy gap (Eg=2.85 eV) and high thermal stability (Tm=106 °C). In addition, to investigate the relationships between the structure and physical properties, the electronic structure and optical properties of BBC crystal were theoretically calculated. This work not only provides a newly chalcone-based NLO crystal, but also presents a feasible molecular design approach by introducing long π-conjugated and halogen substituents.