Tuning Quantum Yield to Maximize Nitric Oxide Release Under Red and NIR Light in Photoresponsive Ruthenium Salen Materials

Photoresponsive Ruthenium salen complexes can release NO under blue, red, and NIR light irradiation. The well-known RuNO(Salen) complex was synthesized initially, which exhibited significant NO release when irradiated with red (627 nm) and NIR (810 nm) light, achieving quantum yields of 0.107 ± 0.01 and 0.00100 ± 0.00007, respectively. Due to the stability and tunability of Salen ligands, further modifications to the Salen structure noticeably influenced the photoreactivity and NO release, where introduction of an -OH group to the 4-position, meta to the imine, emerged as the ideal configuration across to maximize NO release, especially with red and NIR light. Remarkably, incorporating a longer alkyl chain to form the ruthenium-based polymer also significantly enhanced NO release, suggesting improved interactions between the ruthenium center and nitrosated species in polymeric systems that incorporate RuNO(salen) moieties. Additionally, experiments utilizing biological tissue barriers demonstrated that red and NIR light effectively penetrated tissues, stimulating NO release from the RuNO(salen-polymer) in solution, thereby underscoring the potential of these complexes in targeted therapeutic applications. This work elucidates the structure-activity relationship in photoresponsive RuNO(salen) complexes and paves the way for innovative application of materials that can release NO with specific timing and duration of light irradiation, such technology has promising implications in catheter-related infection prevention, where NO release could act as an antimicrobial agent, minimizing infection risk through local, controlled release within catheter systems.