Antenna Tuning in Photoredox Nitric Oxide Releasers for Potent Photovasodilation

To realize spatiotemporal control of nitric oxide (NO), a key signaling molecule for vasodilation in biological systems, we previously developed photocontrollable NO releasers such as NORD-1, whose NO release is triggered by photoinduced electron transfer (PeT) to a light-harvesting moiety. Here, we aimed to improve the PeT-driven NO release by investigating the structure–activity relationship of the rhodamine antenna, focusing on modifications of amino groups at the 3-/6-positions and the element at the 10-position. NO release from selenium- or tellurium-containing NO releasers (NO-SeR and NO-TeR) was significantly enhanced, whereas a phospharhodamine-type NO releaser (NO-POR) exhibited no detectable photodecomposition. Quantum-chemical calculations suggested that the charge-transfer state for NO-POR is stabilized compared to other NO releasers. We confirmed that NO-TeR showed more efficient vasodilation than NORD-1 in ex vivo studies. These findings are expected to facilitate the design of new PeT-driven compounds for biological and therapeutic applications.