Influence of Protonation State on the Excited State Dynamics of a Photobiologically Active Ru(II) Dyad

Abstract

The influence of ligand protonation on the photophysics of a ruthenium (Ru) dyad bearing the 2-(1-pyrenyl)-1H-imidazo[4,5-f][1,10]-phenanthroline (ippy) ligand was investigated by time-resolved transient absorption spectroscopy. It was found that changes in the protonation state of the imidazole group led to changes in the electronic configuration of the lowest lying excited state. Formation of the fully deprotonated imidazole anion resulted in excited state signatures that were consistent with a low-lying intraligand (IL) triplet state. This assignment was supported by time-dependent density functional theory (TDDFT) calculations. IL triplet states have been suggested to be potent mediators of photodynamic effects. Thus, these results are of interest in the design of Ru metal complexes as photosensitizers (PSs) for photodynamic therapy (PDT).

Synthesis, Characterization and Photobiological Studies of Ru(II) Dyads Derived from α‐Oligothiophene Derivatives of 1,10‐Phenanthroline

“…The term metal-organic dyad has been used to describe these Ru(II) complexes that incorporate p-expanded organic chromophores that are tethered to one of the chelating ligands, and these systems were first studied by groups investigating triplet-triplet energy transfer in bichromophoric systems (13). The predicted utility (at the time) of such supramolecular systems was in the area of optoelectronic and luminescencebased technologies, but more recently, their potential in photobiological applications such as PDT/PCT has been recognized (7,(14)(15)(16)(17)(18)(19)(20).…”

Bis[pyrrolyl Ru(ii)] triads: a new class of photosensitizers for metal–organic photodynamic therapy

“…Pure 3 IL states that are lower in energy than the lowest lying 3 MLCT state(s) tend to possess exceptionally long lifetimes (>20 ms) and proved very effective for in vitro PDT. 26,47,[49][50][51][52] From our extensive work in this area, we have found that organic triplets having charge transfer character ( 3 ILCT) contributed by a-oligothienyl groups in certain systems are particularly photoreactive and make excellent PDT agents. 16,48,[53][54][55][56][57][58][59][60][61] Our TLD1433 is one example, which is a bisheteroleptic Ru(II) complex based on the a-terthienylappended imidazo [4,5-f] [1,10]phenanthroline (IP-3T) ligand that generates 1 O 2 with almost unity efficiency.…”

Intracellular Photophysics of an Osmium Complex bearing an Oligothiophene Extended Ligand

“…The photophysical modelsp roposed from the experimental data in this study assumep redominantly one form of the potentially ionizablei midazo group of 1. [56] This comparatives tudy is of particularr elevance as the intracellular photophysicsg overns whether ac ompound will have photocytotoxic effects following light absorption. To truly understandt he photoactivation mechanism, the light-induced processes must not only be examined in solution buta lso within cancer cells.…”

“…As imilar conformer-driven double potentialw as also seen for ap yrene-substitutedR uc omplex. [56] The 3 ILCT cool state on the other hand decayst hrough as ingle pathway by intersystem crossing to the ground state with t b = 146 ns.…”