Photophysics of Pyridylporphyrin Ru(II) Adducts:  Heavy-Atom Effects and Intramolecular Decay Pathways

Abstract

Eight adducts between different pyridylporphyrins and ruthenium complexes, MPyP[RuCl(2)(DMSO)(2)(CO)], c-DPyP[RuCl(2)(DMSO)(2)(CO)](2), TrPyP[RuCl(2)(DMSO)(2)(CO)](3), TPyP[RuCl(2)(DMSO)(2)(CO)](4), (MPyP)(2)[RuCl(2)(DMSO)(2)], [c-DPyP[RuCl(2)(DMSO)(2)]](2), MPyP[RuCl(2)(CO)(3)], and [c-DPyP[RuCl(2)(CO)(2)]](2), have been investigated. The results show that in all the adducts the porphyrin singlet is quenched, to a greater or lesser extent, relative to the parent-free molecule. This study provides insight into the mechanisms of singlet quenching in the adducts. Two mechanisms for singlet quenching, both related to the "heavy-atom effect" of the ruthenium center and experimentally distinguishable by transient spectroscopy, are examined. Enhanced intersystem crossing within the porphyrin chromophore is demonstrated for the series of adducts MPyP[RuCl(2)(DMSO)(2)(CO)], c-DPyP[RuCl(2)(DMSO)(2)(CO)](2), TrPyP[RuCl(2)(DMSO)(2)(CO)](3), and TPyP[RuCl(2)(DMSO)(2)(CO)](4), where a nice correlation is observed between the magnitude of the effect and the number of ruthenium centers attached to the pyridylporphyrin chromophore. Singlet-triplet energy transfer from the pyridylporphyrin chromophore to the ruthenium center(s) is an additional efficient quenching channel for adducts containing ruthenium centers with weak field ligands and low triplet energies, such as (MPyP)(2)[RuCl(2)(DMSO)(2)] and [c-DPyP[RuCl(2)(DMSO)(2)]](2).

Design and Photophysical Properties of Zinc(II) Porphyrin‐Containing Dendrons Linked to a Central Artificial Special Pair

“…Singlet-triplet energy transfers have often been observed in porphyrin-containing dyads. [42] The common feature of these reported dyads is that the porphyrin chromophore, generally zinc(II) porphyrin or the free base, is linked to a fragment prone to fast intersystem crossing, such as a heavy metal (e.g., ruthenium). Herein, this fragment is the paramagnetic Cu II .…”

Metal-Mediated Multi-Porphyrin Discrete Assembliesand Their Photoinduced Properties

“…26), involving different 4 PyPs and octahedral Ru(II) fragments with different ancillary ligands and stereochemistry (cis,cis-RuCl 2 (CO)(dmso-S) 2 and trans,cis-RuCl 2 (dmso-S) 2 ), has been studied [86,87].…”

“…The origin of this lifetime shortening is interesting, since the most obvious quenching mechanisms, singlet energy transfer and photoinduced electron transfer, are prohibited on energetic grounds [87]. A likely explanation of the pyridylporphyrin singlet quenching in the arrays can be identified in the heavy-atom effect of the metal.…”

“…The reasons for the switch in mechanism is not obvious, in the absence of direct information on the triplet energies of the two types of Ru(II) complexes. Ligand field arguments could suggest that the singlet-triplet energy transfer channel may become energetically unavailable for adducts with carbonylcontaining Ru(II) centers [87].…”

Synthesis, Photophysical and Electrochemical Studies on Peripherally Ruthenated Tetraphenylporphyrin

“…In recent times, the physicochemical properties of tetraruthenated metalloporphyrins have been investigated. Its synthesis and photophysical properties of zinc porphyrin and cobalt porphyrin [11][12][13][14], electrocatalytic [15][16][17][18][19], analytical application [20] and DNA interactions [21,22] have been studied. The above mentioned results of peripherally ruthenated porphyrins have one common aspect, i.e., all compounds are based on meso-tetrapyridyl metalloporphyrins.…”