Mechanochromic luminescence (MCL) refers to the reversible color change of solid-state photoluminescence induced by mechanical stimuli. Organic MCL dyes have attracted increasing interest owing to their diverse potential applications, including pressure sensors, rewritable display devices, and information security. However, controlling the range of the mechanically induced shift of the maximum wavelength is a big challenge in developing MCL dyes. Typically, the range of MCL is less than 100 nm for most reported organic MCL dyes. The realization of stepwise emission-color switching in response to mechanical stimuli of different intensity is another emerging challenge. Although several two-step MCL dyes based on a ring-opening reaction induced by strong grinding have been reported, detailed rational guidelines to achieve two-step MCL have not yet been established. Herein, outstanding wide-range MCL over 300 nm and two-step MCL by charge-transfer complexation have been achieved by preparing two-component dyes from dibenzofuran-based bispyrene and typical electron-deficient dyes. The bispyrene showed a bicolor MCL between monomer and excimer emission of the pyrenyl groups. A wide-range MCL that exhibits the shift of the maximum emission wavelength of 340 nm has been achieved by combining bispyrene with 3,4,9,10-perylenetetracarboxylic diimide (PTCDI). The mechanism of the wide-range MCL should be attributed to the formation of segregated crystals and the energy transfer from the pyrenyl group to PTCDI after grinding. Meanwhile, a two-step MCL from blue to blue-green and orange has been achieved for the two-component dye with 9,10-anthraquinone (AQ). The two-step MCL is based on the stepwise formation of the pyrene excimer followed by the formation of the exciplex between bispyrene and AQ.

Tunable mechanochromic luminescence of organic two-component dyes composed of dibenzofuran-based bispyrene and electron-deficient dyes

ACS Spring 2022

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