C14H10BrNO2: A Birefringent Crystal with an Expanded π-Conjugated Group

The construction and synthesis of novel birefringent materials, particularly those characterized by significant birefringence, are of great importance in the field of optical devices and therefore remain a subject of active research. Herein, a new optical crystal material, C14H10BrNO2, was successfully synthesized using a simple solution evaporation method. Its crystal structure comprises two primary structural units, the protonated 9-acridincarboxylic acid hydrate [C14H10NO2]+ and the Br– ion. Notably, C14H10BrNO2 exhibits a birefringence of approximately 0.507 at 550 nm, surpassing the birefringence exhibited by commercially birefringent crystals. The first-principles calculations indicate that the large birefringence observed in C14H10BrNO2 is primarily attributed to the π-conjugated [C14H10NO2]+ group. In addition, C14H10BrNO2 exhibits relatively good thermal stability. This work provides a new insight into the construction of novel birefringent crystals with significant optical anisotropy.