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.