Aggregation-Induced Delayed Fluorescence and Phosphorescence from Hot Excitons via Suppression of Kasha’s Rule in a Stimuli-Active Molecular Rotor
Debasish Barman, Parameswar Krishnan Iyer
Abstract
This work presents a series of through-space donor-alkyl bridge-acceptor (D-σ-A) luminogens, BT2O x Cz [2,2′-(5-(3-(9 H -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 S 7 /S 5 and T 3 ) by suppressing Kasha’s rule. More importantly, the large energy gaps (Δ E ST ) between S 7 /S 5 and S 1 states (T 3 and T 1 states) along with an abundance of small Δ E ST 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.