Electronic structure analysis of copper photoredox catalysts using the quasi-restricted orbital approach

Abstract

In this computational study, the electronic structure changes along the oxidative and reductive quenching cycles of a homoleptic and a heteroleptic prototype Cu(I) photoredox catalyst, namely [Cu(dmp)2]+ (dmp = 2,9-dimethyl-1,10-phenanthroline) and [Cu(phen)(POP)]+ (POP = bis[2-(diphenylphosphino)phenyl]ether) are scrutinized and characterized using quasi-restricted orbitals (QRO), electron density differences and spin densities. After validating our density functional theory-based computational protocol, the equilibrium geometries and wavefunctions (using QROs and atom/fragment compositions) of the four states involved in photoredox cycle (S0, T1, Dox and Dred) are systematically and thoroughly described. The formal ground and excited state ligand- and metal-centered redox events are substantiated by the QRO description of the open-shell triplet 3MLCT (d9L-1), Dox (d9L0) and Dred (d10L-1) species and the corresponding structural changes, e.g., flattening distortion, shortening/elongation of Cu-N/Cu-P bonds, are rationalized in terms of the underlying electronic structure transformations. Amongst others, we reveal the molecular-scale delocalization of the ligand-centered radical in the a 3MLCT (d9L-1) and Dred (d9L-1) states of homoleptic [Cu(dmp)2]+ and its localization to the redox-active phenanthroline ligand in the case of heteroleptic [Cu(phen)(POP)]+.

Structural change dynamics of heteroleptic Cu(i) complexes observed by ultrafast emission spectroscopy

“…13,15,21,24,47 Recently, heteroleptic copper(I) complexes, which have both phosphine and diimine ligands, have attracted attention because this class of Cu complexes exhibit attractive and advanced photochemical and photophysical properties. [48][49][50][51][52][53][54][55][56][57][58] Especially, [Cu(I)(dmp)(P) 2 ] + (dmp = 2,9-dimethyl-1,10-phenanthroline derivatives; P = phosphine ligand) (Fig. 1) has big potential to work as a photosensitizer in photocatalytic systems.…”

Photoactive Copper Complexes: Properties and Applications

“…The electronic structural changes involved in the oxidative and reductive quenching cycles of [Cu­(dmp) 2 ] + ([Cu­( NN 2 ) 2 ] + ) and [Cu­(phen)­(DPEphos)] + ([Cu­( NN 1 )­( PP 1 )] + ) have been studied using the quasi-restricted orbital approach, electron density differences, and spin densities. The corresponding structural changes such as flattening distortion and shortening/elongation of Cu−N/Cu−P bonds are rationalized in terms of these electronic structural changes . In a similar perspective, a series of heteroleptic copper­(I) complexes of general structures [Cu­( NN )­(DPEphos)] + ([Cu­( NN )­( PP 1 )] + ), with various phenanthroline-based ligands substituted at their 2 and 9 positions by different alkyl chains and at their 4 and 7 positions by either phenyl groups or hydrogen atoms, were investigated using DFT and TD-DFT, with the complexes containing moderately bulky ligands at their 2 and 9 positions and phenyl groups at the 4 and 7 positions of the phenanthroline ligands being the best light emitters .…”

Computational Chemistry as Applied in Environmental Research: Opportunities and Challenges

“…In recent years, other hybrid functionals have gained use in the detriment of B3LYP (e.g., TPSSh and the double hybrid M062X) . TPSSh has been cataloged among the 20 best-performing functionals for calculating barrier heights and binding energies and accurately describing electron transfer processes. ,, Double hybrid functionals (e.g., M062X and B2PLYP) have reached the highest level of accuracy to date, yet their increased computational cost makes difficult their application to larger systems …”

“…108 TPSSh has been cataloged among the 20 best-performing functionals for calculating barrier heights and binding energies and accurately describing electron transfer processes. 102,109,110 Double hybrid functionals (e.g., M062X and B2PLYP) have reached the highest level of accuracy to date, yet their increased computational cost makes difficult their application to larger systems. 111 In the HF or DFT formalisms, the wave function is expressed in terms of one-electron orbitals (MO approach).…”

“…124,146,147 One of the most common approaches is employing the Born−Haber thermodynamic cycle to compute the Gibbs free energy change for the reduction half-reaction (ΔG 0 ), which yields the E 0 . 110,124 As mentioned above, caution should be taken to select appropriate levels of theory and solvation parameters. The choice of the potential of the reference electrode is also an aspect that can induce errors in the calculation.…”