Optical properties and red to near infrared piezo-responsive fluorescence of a tetraphenylethene–perylenebisimide–tetraphenylethene triad

Abstract

The optical properties and piezofluorochromic behaviour of N,N′-dioctyl-1,7-di(4-(1,2,2-triphenyl)vinyl)phenyl-3,4:9,10-tetracarboxylic perylenebisimide (PBI–TPE) have been investigated. PBI–TPE shows strong fluorescence in non-polar solvents, in contrast to complete quenching in common moderately polar to polar solvents, most likely due to intramolecular charge transfer (ICT) from the donating tetraphenylethene (TPE) groups to the acceptor perylenebisimide core. The solid-state fluorescence is morphology dependent, in which the amorphous-state displays near infra-red emission at 744 nm and the crystalline state shows a blue-shift in emission at 665 nm with a difference of 79 nm. Crystalline PBI–TPE exhibits stress induced amorphisation resulting in a piezo-responsive behaviour in which the metastable amorphous state and crystalline state can be interconverted by grinding and thermal annealing (200 °C)/recrystallisation. This reciprocal conversion gives rise to the piezofluorochromic effect. Finally, crystalline microstructures were used to fabricate a microwire field-effect transistor (MFET) with the effective mobility (μ_e) and capacitance (C_i) estimated to be 3.11 × 10⁻⁵ cm² V⁻¹ s⁻¹ and 1.51 × 10⁻¹⁵ F, respectively.