Understanding the\nStructural Modulations in Twisted\nDonor–Acceptor–Donor (D-A-D) Systems for Boosting Type\nI Photosensitizing Photocatalytic Activity

Supramolecular assemblies based on the twisted donor–acceptor–donor\n(D-A-D) building block <b>Qx-Ind</b> have been developed, which\ninterestingly, due to the balanced angle of twist (38.28°), high\nintermolecular charge transfer, and crystallization induced emission\n(CIE) characteristics, exhibit high molar absorptivity and a long-lived\n“lighted” excited state at the supramolecular level.\nThe validity of the design concept was examined by preparing CIE active\nD-A-D system <b>Qx-Indaz</b> (weak donor, low angle of twist:\n35.45°), in which, due to the insertion of an additional binding\nsite for noncovalent interactions, a drastic change in the photophysical\nbehavior is observed. The combined spectroscopic studies of all the\ncompounds unveil the strong impact of modulation of the angle of twist\nand intermolecular charge transfer upon photophysical behavior in\nthe aggregated state. Due to the favorable photophysical behavior,\nthe supramolecular assemblies of <b>Qx-Ind</b> exhibit high\ntype I photosensitizing activity in comparison to <b>Qx-Indaz</b>. The superior type I photosensitizing activity of <b>Qx-Ind</b> assemblies is manifested in their ability to efficiently catalyze\nthe aerobic oxidative synthesis of quinazolin-4(3<i>H</i>)-ones (via type I ROS) from 2-aminobenzamide and aromatic aldehydes\nin the absence of additional additives (base/oxidant). Unlike photocatalytic\nnanoassemblies reported in the literature, due to the CIE characteristics, <b>Qx-Ind</b> does not require preliminary preparation and could\nbe directly introduced in the solid state to reaction media. Thus,\nthe present work demonstrates a simple strategy of upgrading type\nI photosensitizing activity by improving the ground/excited state\nbehavior of a twisted D-A-D system through modulation of the angle\nof twist and charge transfer characteristics.