Effect of Delocalization and Rigidity in the Acceptor Ligand on MLCT Excited-State Decay

Abstract

In its most simple form, the energy gap law for excited-state nonradiative decay predicts a linear dependence of ln k(nr) on the ground- to excited-state energy gap, where k(nr) is the rate constant for nonradiative decay. At this level of approximation, the energy gap law has been successfully applied to nonradiative decay in a wide array of MLCT excited states of polypyridyl complexes of Re(I), Ru(II), and Os(II). This relationship also predicts a dependence of k(nr) on the structural characteristics of the acceptor ligand. We report here a brief survey of the literature which suggests that such effects exist and have their origin in the extent of delocalization of the excited electron in the ligand pi framework and on acceptor ligand rigidity.

Controlling the emission efficiency of blue-green iridium(iii) phosphorescent emitters and applications in solution-processed organic light-emitting diodes

“…Upon degassing, k r shows essentially no net change for 1b/2b, while k nr decreases by two orders of magnitude. We attribute the low Φ PL values observed for 1a and 2a to strong vibrational coupling 10,14,16 principally among the asymmetric stretching modes of the Ir--N dFppy bonds and the asymmetric stretching modes of the C--N and C--C bonds of the pyridine ring of the CF 3 --gpy in 1aand 2a.This hypothesis is corroborated by DFT calculations where the LUMO (lowest unoccupied molecular orbital) is switched from the CF 3 --gpy moiety in 2a to the pyridine unit of the C^N ligands in 2b (Fig. 4); a similar relationship exists for 1a/1b (Fig.…”

“…Upon degassing, k r shows essentially no net change for 1b/2b, while k nr decreases by two orders of magnitude. We attribute the low Φ PL values observed for 1a and 2a to strong vibrational coupling 10,14,16 principally among the asymmetric stretching modes of the Ir--N dFppy bonds and the asymmetric stretching modes of the C--N and C--C bonds of the pyridine ring of the CF 3 --gpy in 1aand 2a.…”

Conversion of CO2 via Visible Light Promoted Homogeneous Redox Catalysis

“…In the weakly emitting Ru(II) polypyridine complexes the nonradiative decay constant is the more important factor [30]. Beside direct contributions from the ground state, this nonradiative decay can be reached via a thermally accessible metal-centered state ( 3 MC).…”

Red Phosphorescence in RuII Complexes of a Tridentate N‐Heterocyclic Carbene Ligand Incorporating Tetrahydropyrimidine

“…[11,[22][23][24][25][26][27] However, lowering of the 3 MLCT state renders the complex less useful for photosensitizer applications, owing to the usual deactivation pathway for low-energy emitting ruthenium(II) complexes according to the energy gap law. [1,10,28,29] Recently, Hammarström and Johansson [30][31][32] demonstrated that design of tridentate ligands with larger bite angles than tpy can produce octahedral complexes that lead to a greater 3 MLCT-3 MC gap and hence longer excited-state lifetimes. Further studies by Ruben [33] and Heinze [34] show a similar effect.…”