Caging and photo-triggered uncaging of singlet oxygen by excited state engineering of electron donor-acceptor-linked molecular sensors.

Singlet oxygen (O), one of the most sought-after species in oxidative chemical reactions and photodynamic cancer therapy, is activated and neutralized in the atmosphere and living cells. It is essential to see "when" and "where" O is produced and delivered to understand and utilize it. There is an increasing demand for molecular sensor tools to capture, store, and supply O, controlled by light and engineered singlet and triplet states, indicating the O-capturing-releasing state. Here, we demonstrate the outstanding potential of an aminocoumarin-methylanthracene-based electron donor-acceptor molecule (1). Spectroscopic measurements confirm the formation of an endoperoxide (1-O) which is not strongly fluorescent and remarkably different from previously reported O sensor molecules. Moreover, the photoexcitation on the dye in 1-O triggers fluorescence enhancement by the oxidative rearrangement and a competing O release. The unique ability of 1 will pave the way for the spatially and temporally controlled utilization of O in various areas such as chemical reactions and phototherapies.