Synthesis and Emission Properties of a Series of 2,3,4,5-Tetrakis(5-aryl-2-thienyl)-1-phenylpyrroles as a Sterically-crowded Star-shaped D-(π-A)4 Molecule

A series of 2,3,4,5-tetrakis(5-aryl-2-thienyl)-1-phenylpyrroles with different acceptor-type aryl terminals (Ar = p-CN-C6H4, p-CHO-C6H4, p-NO2-C6H4) have been synthesized. The synthesized compounds, possessing a sterically-crowded star-shaped D-(π-A)4 structure, exhibited a significantly large Stokes shifted emission from the planarized intramolecular charge transfer (PLICT) state of the flattened 2,5-bis(5-aryl-2-thienyl)pyrrole component. It was found that the PLICT states of these compounds result in an inherent positive fluorosolvatochromism with different emission color changes due to their different ICT degrees.