Aggregation-Induced Delayed Fluorescence and Phosphorescence from Hot Excitons via Suppression of Kasha’s Rule in a Stimuli-Active Molecular Rotor

This work presents a series of through-space donor-alkyl bridge-acceptor (D-σ-A) luminogens, BT2OxCz [2,2′-(5-(3-(9H-carbazol-9-yl)alkoxy)-1,3-phenylene)bis(benzothiazole)] (x = 3, 4, 5, and 6), as anti-Kasha emissive multifunctional molecular rotors with in-depth mechanistic insights, conveyed by experimental and theoretical results. The origin of aggregation-induced emission and coexistence of dual fluorescence and phosphorescence are realized from hot excitons (especially from the bright emissive states of S7/S5 and T3) by suppressing Kasha’s rule. More importantly, the large energy gaps (ΔEST) between S7/S5 and S1 states (T3 and T1 states) along with an abundance of small ΔEST between singlet charge transfer and triplet locally excited states facilitate reverse intersystem crossing resulting in thermally activated delayed fluorescence and room-temperature phosphorescence simultaneously. Besides, alkyl chain length-induced distinct H- and J-aggregation offers tunable triplet-harvesting behavior and white-light emission along with two different reversible mechanoresponsive properties viz. mechanoluminescence and mechanochromism, respectively.