Room-Temperature Stable Noncovalent Charge-Transfer Dianion Biradical to Produce Singlet Oxygen by Visible or Near-Infrared Light Photoexcitation

Noncovalent interaction between small molecules can generate a charge-transfer (CT) state, achieving the effect of a conjugated large molecule as well as a transition-metal complex. Herein, we demonstrate a room-temperature stable dianion biradical conveniently produced by noncovalent intermolecular CT interaction between anthraquinone (AQ) and potassium tert-butoxide (KOtBu). Essentially, CT from KOtBu to AQ boosts absorption bands from the UV to visible and near-infrared (NIR) range, enabling AQ-KOtBu to have new absorption bands around 400, 550, and 900 nm. The absorption bands of AQ-KOtBu are dramatically enhanced after blue-to-green or NIR light excitation. Interestingly, both ground state AQ–KOtBu (C(1)) and photoexcited AQ–KOtBu (C(2)) are quenched by oxygen to produce singlet oxygen. Furthermore, C(1) can be photoactivated by purged nitrogen in solution, and C(2) can be regenerated after the photoexcitation and purged nitrogen in solution, which may serve as a photosensitizer under visible and NIR light excitation.