Photolysis of [Ru(bipy)2(NO)Cl](PF6)2 in frozen ionic glass matrices. Evidence for nitrosyl linkage isomerism and NO-loss in a physiologically relevant nitric oxide source

CASPT2 Potential Energy Curves for NO Dissociation in a Ruthenium Nitrosyl Complex

“…The main mechanistic assumptions for the determination of the NO • photorelease pathways is that i) this process occurs from the lowest triplet excited states, as suggested by the rapid population of these states after initial irradiation and ultrafast intersystem crossing (ISC) [45,49,53], and that ii) it involves initially a decoordination of the NO • radical [19,22]. According to i), three triplet-state intermediates ( Figure 2) were located on the lowest triplet potential energy surface at the DFT level [43,44,50].…”

“…Ruthenium nitrosyl complexes have attracted considerable interest over the last decades because of their multifunctional photoresponsive capability. Indeed, these complexes can display photochromism in the solid state [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] and be efficient agents for NO photorelease in solution [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. Despite the numerous studies exploiting these two distinct photoreactivities (i.e., N→O linkage photoisomerization and photoinduced NO delivery), the underlying mechanisms are notoriously complex to unravel based on the available experimental observations [12,30].…”

“…Although a vast majority of computational studies are dealing with organic photochemistry [32][33][34][35] due to the difficulty of computing photochemical pathways in metal complexes [36], recent computational investigations of photoisomerizable metal complexes have been published with the aim of understanding their photoswitching mechanisms [37][38][39][40][41][42][43][44][45]. Regarding ruthenium nitrosyl complexes, the N→O linkage photoisomerization mechanism in the trans-[RuCl(NO)(py) 4 ] 2+ (where py denotes a pyridine ligand) complex was investigated using density functional theory (DFT) and multi-state complete active space second-order perturbation theory photorelease could be observed, suggesting that weakly bound linkage isomers of nitric oxide are likely intermediates in the photolytic release of NO • [19,22]. Very few theoretical studies have been devoted to NO • photorelease.…”

“…The mechanism for NO • photorelease is important, as this radical is involved in various physiological and pathological processes [46] and ruthenium nitrosyl complexes can be designed to promote NO • photorelease, in particular using low-power light for biological and medicinal applications [24,26,29,47,48]. Experimental studies in the solid phase have shown that the photoproducts of both N→O linkage photoisomerization and NO • photorelease could be observed, suggesting that weakly bound linkage isomers of nitric oxide are likely intermediates in the photolytic release of NO • [19,22]. Very few theoretical studies have been devoted to NO • photorelease.…”

A Theoretical Study of the N to O Linkage Photoisomerization Efficiency in a Series of Ruthenium Mononitrosyl Complexes

“…Owing to the difficulty of computing photochemical pathways in metal complexes [ 34 ], the number of theoretical studies devoted to the linkage photoisomerization mechanisms in these systems is unsurprisingly low [ 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 ]. Among these systems, ruthenium nitrosyl complexes have attracted considerable interest due to both their photochromic properties [ 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 ] and their capability to release nitric oxide [ 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 ]. Recently, the N→O linkage photoisomerization mechanism in the trans -[RuCl(NO)(py) 4 ] 2+ (where py denotes a pyridine ligand) ruthenium nitrosyl complex was investigated based on density functional theory (DFT) calculations of the lowest singlet and triplet potential energy profiles along the N→O linkage photoisomerization coordinate [ 41 , 42 ].…”