Fumaronitrile-based π–conjugated mechanochromic material: Design, synthesis and photophysical properties

Abstract

In this study, we synthesized four 2,3-bis(4-methoxyphenyl)fumaronitrile-based D–A–D quadrupoles using a two-fold Suzuki-Miyara cross-coupling reaction and conducted comprehensive investigations into their photophysical properties, including absorption, fluorescence, and lifetime in the solution state. All compounds demonstrate a blue to green light emission both in solution and thin films, alongside moderate quantum yields and lifetimes (in the nanosecond range) in solution state, while also presenting significant spectral shifts in thin films. Aggregation-induced emission (AIE) behavior in THF/water mixtures and solvatochromic effects were observed by varying the solvent polarities. The energy levels of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were examined via density functional theory (DFT) calculations. Intriguingly, mechanical force application, such as grinding, induced a red shift in the photoluminescence spectra, while exposure to dichloromethane fumes resulted in reversible spectra changes. These distinct behaviors underscore the mechanochromic nature of the compounds, as corroborated by both photoluminescence and powder-XRD analyses. Importantly, these unique characteristics render the compounds suitable for applications in inkless pens and rewritable printers.