A Study of the Functionalisation of BOPYIN Dyes: Synthesis and Photophysical Properties

Borondifluoride-3,3-dimethyl-2-[2-(2-pyrrolyl) ethenyl] indole (BOPYIN), a seven-membered, nonplanar boron complex, features typical photophysical properties, such as relatively large Stokes shift. Herein, a series of BOPYINs are prepared by a two-step, one-flask synthesis. Based on the modification position, these derivatives could be divided into three sections, including withdrawing substituted dyes, dyes with donating substitution on the pyrrole unit, and dyes with further pi-enlarged substitution on indole unit. The relationship between diverse modified structures and photophysical properties are systematically discussed by experiments and DFT calculations. This work illustrates that donating-group modifications on pyrrole and pi-enlargement on the indole unit may promote the red shift of the photophysical spectra synergistically.