Polymorphism-Dependent Enhanced Emission in Molecular Aggregates: J-Aggregate versus X-Aggregate
Suqian Ma, Yingjie Liu, Jibo Zhang, Bin Xu, Wenjing Tian
Abstract
The photoluminescence properties of organic fluorescent materials in the solid state are closely related to their aggregation structures. Herein, we present an organic fluorescent molecule 9,10-bis(2,2-di(4-fluorophenyl)vinyl)anthracene (BDFVA) with two crystal polymorphisms to provide an ideal molecular model for understanding the nature of luminescence from the J- and X-aggregates. Detailed structural and photophysical studies reveal that both J- and X-aggregate crystals exhibit enhanced emission in comparison with the corresponding dilute solution because of crystallization-induced emission enhancement (CIEE). Additionally, the X-aggregate (B-phase) crystal with crossed molecular packing exhibits a higher fluorescence efficiency (ΦF = 0.60), giving a 1.4-fold promotion of ΦF compared to the J-aggregate crystal (G-phase) with staggered molecular packing because the split excited states are all optically allowed in the X-aggregate. Optical waveguide experiments show that the two crystals exhibit excellent amplified spontaneous emission (ASE), demonstrating a promising potential application in organic solid-state lasers.