Dual fluorescence polymorphs: Wide-range emission from blue to red regulated by TICT and their dynamic electron state behavior under external pressure

Abstract

Organic fluorescence molecules have attracted great interest in the last decades, due to their adjustable fluorescence properties and broad applications in organic electroluminescence display, fluorescence labelling, biological imaging, and so on. Conformation is one of the most important factors that determines organic molecular fluorescence properties. Herein, a compound, DBTO-PTZ, with five polymorphs was demonstrated. Distinctive polymorph-dependent optical characteristics were observed in these polymorphs, which gives an ideal model for the investigation of relationship between conformation and fluorescence property. Three of them display distinct dual fluorescence which is not observed in solution or the other two crystals. It is found that the twist angle between DBTO and PTZ units is a critical factor to determine the polymorphs of DBTO-PTZ and corresponding fluorescence behaviors. This result provides a direct proof to support the TICT model. Moreover, the external pressure was applied to adjust the fluorescence behavior from a dual emission to a single LE emission, which further proves the mechanism of TICT. This work will contribute to the understanding between conformation and optical characteristics. It also sheds light on a new strategy to fine-tune the fluorescence property.