Effect of an amine functionalization of phenanthroline ligand associated with an ester-pyridine ligand on excited-state properties of Re(I) complex. Interplay between two 3MLCT

Abstract

In this work, the synthesis, characterization and photophysical properties of rhenium(I) polypyridyl compound, fac-[Re(et-isonic)(NH2phen)(CO)3]PF6, where NH2phen = 5-amino-1,10-phenanthroline and et-isonic = ethyl isonicotinate, are reported. The compound exhibited a broad absorption band around 300–500 nm that by Time-Dependent Density Functional Theory (TD-DFT) corresponds to a mixture of ILNH2phen and MLCTRe→NH2phen transitions and a contribution of the charge transfer transition MLCTRe→et-isonic. Contrary to what is expected, the change of Cl (λmax = 490 and 565 nm; ϕ = 0.002; τ = 0.49 ± 0.07 μs and < 0.020 μs) for et-isonic ligand (λmax = 590 nm; ϕ = 0.003; τ = 0.43 ± 0.03 μs and 0.044 ± 0.014 μs), a π-acceptor ligand, promoted a bathochromic shift of the emission maxima in acetonitrile solution. This distinct behavior can be rationalized in terms of the inversion of the lowest-lying excited state of the usual observed MLCTRe→NN to the unusual MLCTRe→et-isonic. On the other hand, the contribution of ligand-based excited state in the deactivation process cannot be ruled out. Additionally, as a triplet emitter, a high quantum yield for the singlet oxygen generation (0.50 ± 0.03) can be associated with either, 3MLCT or a 3LC state. The photophysics ally to the higher singlet oxygen generation reported herein provides new fundamental insights into the understanding of substituent groups on the polypyridyl ligands that are relevant to the practical development of the scientific field.