The effect of –CF3 substitution position on the aggregation-induced emission, solvatofluorochromism and mechanofluorochromism properties of the conjugated 9-butyl-9H-carbazole phenylacrylonitrile derivatives

Abstract

A series of 9-butyl-9H-carbazole derivatives with intense solid-state emission were synthesised by the Knoevenagel reaction of 9-butyl-9H-carbazole-3-carbaldehyde with phenyl acetonitrile derivatives with –CF3 group at different substituent positions of the phenyl group. They exhibit remarkable aggregation-induced emission (AIE), solvatofluorochromism and mechanofluorochromic (MFC) properties depending on the –CF3 substitution site. The ortho-substituted derivative shows enhanced charge transfer properties with a distinct dual-state fluorescence emission. This peculiar property is further utilised for data encryption and anti-counterfeiting applications. The para-substituted derivative exhibits an increased solid-state fluorescence quantum yield of 88% with switchable MFC properties. The ground and excited state photophysical properties of the synthesised luminogens were explored using various spectroscopic techniques. The study provides an efficient strategy to understand the effect of the –CF3 substitution position in tuning and modifying the luminescence properties of the organic solids via subtle modifications in the molecular scaffolds.