Through-Space Charge-Transfer-Based Aggregation-Induced Emission and Thermally Activated Delayed Fluorescence in Fused 2H-Chromene Coumarin Congener Generating ROS for Antiviral (SARS-CoV-2) Approach.

Harvesting triplets in metal-free organic frameworks at ambient conditions and finding appropriate applications are a formidable challenge. Herein, we report a donor-acceptor-type system composed of carbazole and fused 2-chromene coumarin derivative, exhibiting triplet harvesting thermally activated delayed fluorescence (TADF) and aggregation-induced emission (AIE) behavior in solid and aggregated states, respectively. The presence of an sp linker and the introduction of a selected cyano/ester group in the acceptor result in twisted D-A architectures, further assisting in the suppression of nonradiative deactivation via through-space charge transfer and H-bonding interactions, fulfilling the stringent requirements for the simultaneous process of TADF and AIE, successively. Experimental and theoretical results revealed that the participation of the singlet/triplet charge transfer (CT/CT) and the higher lying hybrid triplet locally excited charge-transfer state (LE + CT) leads to an efficient TADF. Both of the synthesized AIE-TADF congeners actively participated in the generation of reactive oxygen species (ROS) in nanoaggregate forms and were further explored computationally for antiviral prospects as inhibitors of the SARS-CoV-2 spike protein.