Excited state decay of cyclometalated polypyridine ruthenium complexes: insight from theory and experiment

Abstract

Deactivation pathways of the triplet metal-to-ligand charge transfer ((3)MLCT) excited state of cyclometalated polypyridine ruthenium complexes with [RuN5C](+) coordination are discussed on the basis of the available experimental data and a series of density functional theory calculations. Three different complex classes are considered, namely with [Ru(N^N)2(N^C)](+), [Ru(N^N^N)(N^C^N)](+) and [Ru(N^N^N)(N^N^C)](+) coordination modes. Excited state deactivation in these complex types proceeds via five distinct decay channels. Vibronic coupling of the (3)MLCT state to high-energy oscillators of the singlet ground state ((1)GS) allows tunneling to the ground state followed by vibrational relaxation (path A). A ligand field excited state ((3)MC) is thermally accessible via a (3)MLCT →(3)MC transition state with the (3)MC state being strongly coupled to the (1)GS surface via a low-energy minimum energy crossing point (path B). Furthermore, a (3)MLCT →(1)GS surface crossing point directly couples the triplet and singlet potential energy surfaces (path C). Charge transfer states either with higher singlet character or with different orbital parentage and intrinsic symmetry restrictions are thermally populated which promote non-radiative decay via tunneling to the (1)GS state (path D). Finally, the excited state can decay via phosphorescence (path E). The dominant deactivation pathways differ for the three individual complex classes. The implications of these findings for isoelectronic iridium(iii) or iron(ii) complexes are discussed. Ultimately, strategies for optimizing the emission efficiencies of cyclometalated polypyridine complexes of d(6)-metal ions, especially Ru(II), are suggested.

Towards Water Soluble Mitochondria-Targeting Theranostic Osmium(II) Triazole-Based Complexes

“…Curiously, unlike in the case of 2, the T1 state of 1 undergoes a puckering like distortion of the btzpy ligand on which the unpaired electron density is localized. Such distortions have been observed, however, in theoretical calculations of the T1 states of bis(tridentate) ruthenium(II) cyclometalated complexes [48] and [Os(terpy)2] 2+ [49].…”

Deuterated Molecular Ruby with Record Luminescence Quantum Yield

“…[8] Emerging novel applications of these extraordinary emitters such as triplet-triplet annihilation upconversion, [6a] demanding photoredox reactions, [6] optical temperature sensing with as ingle dye [10] and selective energy transfer/singlet oxygen formation [11] have already been realized in this short time and ap lethora of others are expected in the future. [20,21] In octahedral ligand fields the emissive 2 Es tate of 1 3+ is essentially undistorted relative to the 4 A 2 ground state resulting in nested states ( Figure 1). [12,13] Especially, chromium(III) complexes enjoy ag rowing interest in these areas.…”

Engineering Tunable Single and Dual Optical Emission from Ru(II)–Polypyridyl Complexes through Excited State Design

“…[18][19][20][21][22][23][24][25][26] The further design and control of optical materials based on Ru-polypyridyl will require an explanation and predictive prescription for, perhaps, their most intriguing optical aspect -the observation of single and dual optical emission. [27][28][29][30][31][32][33][34][35][36][37][38] In general, dual emission properties in organometallic complexes may arise from two different 3 MLCT states involving different ligands, from types of states e.g. 3 MLCT, 3 IL or 3 LL'CT or based on different metals in dissymmetric bimetallics complexes.…”