Conformationally gated photoinduced processes within photosensitizer-acceptor dyads based on ruthenium(II) and osmium(II) polypyridyl complexes with an appended pyridinium group

Abstract This review deals with some identified consequences of excited-state conformational relaxations on photoinduced processes taking place within semi-rigid and potentially π-conjugated inorganic multicomponent systems. Planarization is the hallmark of structural upheavals herein considered. This ultrafast and widespread phenomenon is shown to occur upon various types of photoinduced charge redistributions at the intramolecular level, which span from mere metal-to-ligand charge transfer (MLCT) to charge separated (CS) state formation. Having first being reminded of the various aspects which constitute the general context of this review, that is supramolecular inorganic photochemistry, and put in perspective the plural status of intramolecular conformation, we shall assess the possible substantial changes in the photophysical features of luminophores following from planarization. Then, the impact of the excited-state planarization on the interplay between functional subunits via the modification of intercomponent electronic coupling, is discussed. Special emphasis is put on (closely coupled) dyads comprised of a photoactive coordination compound (typically of the ruthenium(II)-trisbipyridyl or osmium(II)-bisterpyridyl type) as both the photosensitizer and the primary light-triggered electron donor, and of a substituted pyridinium group as the electron acceptor. Implementation of conformational gating of photoinduced processes for molecular electronics or sensing devices is finally mentioned.