Photochemistry and Photophysics of Coordination Compounds: Rhodium

Abstract

Rhodium(III) polypyridine complexes and their cyclometalated analogues display photophysical properties of considerable interest, both from a fundamental viewpoint and in terms of the possible applications. In mononuclear polypyridine complexes, the photophysics and photochemistry are determined by the interplay between LC and MC excited states, with relative energies depending critically on the metal coordination environment. In cyclometalated complexes, the covalent character of the C – Rh bonds makes the lowest excited state classification less clear cut, with strong mixing of LC, MLCT, and LLCT character being usually observed. In redox reactions, Rh(III) polypyridine units can behave as good electron acceptors and strong photo-oxidants. These properties are exploited in polynuclear complexes and supramolecular systems containing these units. In particular, Ru(II)-Rh(III) dyads have been actively investigated for the study of photoinduced electron transfer, with specific interest in driving force, distance, and bridging ligand effects. Among systems of higher nuclearity undergoing photoinduced electron transfer, of particular interest are polynuclear complexes where rhodium dihalo polypyridine units, thanks to their Rh(III)/Rh(I) redox behavior, can act as twoelectron storage components. A large amount of work has been devoted to the use of Rh(III) polypyridine complexes as intercalators for DNA. In this role, they have proven to be very versatile, being used for direct strand photocleavage marking the site of intercalation, to induce long-distance photochemical damage or dimer repair, or to act as electron acceptors in long-range electron transfer processes

Metal centered ligand field excited states: Their roles in the design and performance of transition metal based photochemical molecular devices

“…When the temperature is raised from Adapted from Refs. [153,156]. 77 K to room temperature, the dicyano complex continues to show only 3 LC emission, indicating that the 3 MC state remains thermally inaccessible over this temperature range.…”

“…23) [153,154]. The stronger -donor character of C − relative to N results in several important differences between complexes with cyclometallating ligands and those of polypyridine ligands.…”

“…The photophysical properties of Rh(III) [153] and Ir(III) [154] polypyridine complexes has been reviewed elsewhere but is briefly discussed here to highlight some differences and similarities with the Fe(II), Ru(II), and Os(II) systems. Representative of this class of complexes is Rh(phen) 3 3+ which exhibits intense (˚= 1) longlived ( = 48 ms) structured emission in 77 K matrices.…”

Metalloligands: Rhodium(III) Cyclometallated Compounds Containing Multitopological Binucleating Ligands

“…The connectivity of the binucleating ligand diisoamyldithiooxamidate within the bimetallic complexes has been assessed. The linkage isomer obtained is [Rh(2-phenylpyridine) 2 {µ-(isoamyl) 2 ated fragment, an interesting photoelectrochemical probe, [5] and in exploring their reactivity toward other metal fragments. The aim is to get heteropolymetallic complexes in which the electronic communication between the metals is propagated through bridging atoms.…”

Metal-Based Molecular Functional Materials - From Discrete Metal Complexes to Supramolecular Assembly, Nanostructures and Functions

“…1 These have provided insights into the exploration of molecular-based functional materials with concepts of supramolecular photochemistry. [1][2][3][4][5][6] In addition to the ruthenium(II) polypyridine system, researchers also investigated the photophysics and photochemistry of iridium(III) system because of their synthetic versatility, high photo-and thermal stabilities with tunable emission color and thus can be applied as triplet emitters and phosphorescent dopants in organic light emitting devices (OLEDs). [7][8][9][10][11][12][13] In addition, lots of efforts have also been devoted into the exploration of new classes of luminescent transition metalligand chromophores and their application in materials chemistry and science by understanding and rationalization of their excited state properties.…”