Crystallization-Induced Red Phosphorescence and Grinding-Induced Blue-Shifted Emission of a Benzobis(1,2,5-thiadiazole)-Thiophene Conjugate

Abstract

Mechanochromic luminogens are of significant importance in both academic and technical aspects. Thus far, most mechanochromic compounds exhibit bathochromically shifted emission upon grinding; the examples of those that exhibit blue-shifted emission still remain limited. Herein, a donor-acceptor-donor (D-A-D)-structured conjugate, namely 4,7-di(2-thienyl)-2,1,3-benzothiadiazole (DTBT), comprising benzobis(1,2,5-thiadiazole) and thiophene units, has been carefully synthesized and investigated. DTBT exhibits typical intramolecular charge transfer (ICT) characteristics, crystallization-induced phosphorescence (CIP), and remarkable mechanochromism. Although it merely emits fluorescence in solutions with distinct ICT features, its crystals demonstrate bright-red room-temperature phosphorescence (616 nm) with efficiency up to 25.0% and generate yellow excimer fluorescence (578 nm) upon mechanical grinding, accompanying decreased lifetimes from 10.9 μs to 3.5 ns and a blue-shifted emission of 38 nm. These results highly indicate the feasibility to fabricate novel CIP luminogens with blue-shifted mechanochromism.