Contrasting photophysical properties of rhenium(I) tricarbonyl complexes having carbazole groups attached to the polypyridine ligand

Author(s)

Ramos, L. D. ; Sampaio, R. N. ; de Assis, F. F. ; de Oliveira, K. T. ; Homem-de-Mello, P. ; Patrocinio, A. O. T. ; Frin, K. P. M.

• Document type: Journal article
• Source: DALTON TRANSACTIONS; v. 45, n. 29, p. 11688-11698, 2016.
• Web of Science Citations: 13

Abstract

In the present work, new rhenium(I) polypyridyl compounds, fac-{[}Re(L)(CO)(3)(cbz(2)phen)](+/0) where cbz(2)phen = 4,7-di(9H-carbazol-9-yl)-1,10-phenanthroline and L = Cl-, pyridine (py) or 2-aminomethylpyridine (ampy) were synthesized and characterized by H-1 NMR, UV-Vis and IR spectroscopy combined with theoretical calculations using time-dependent density functional theory (TD-DFT). Their photophysical properties were investigated by steady state and time-resolved emission spectroscopy. These compounds show a strong and broad absorption band around 350-500 nm that, also by TD-DFT, corresponds to the carbazol -> phenanthroline intraligand charge transfer transition, (ILCTcbz2phen)-I-1, with some contribution of the Re(I) -> phenanthroline metal-to-ligand charge transfer transition, (MLCTRe -> cbz2phen)-M-1. In contrast to typical Re(I) polypyridyl complexes, cbz(2)phen-based Re(I) compounds exhibit two emission maxima in CH3CN solution and relatively low emission quantum yields, 10(-3)-10(-2). Solution phase time-resolved photoluminescence and excited state quenching experiments provided meaningful information on the presence of multiple emitter states after light excitation, which were identified as an (ILCTcbz2phen)-I-1 excited state deactivation at higher energies and a long-lived phosphorescence attributed to the (MLCTRe -> cbz2phen)-M-3 excited state. When embedded into a PMMA matrix, the radiative decay from the singlet state is inhibited and the contribution of both (MLCT)-M-3 and 3(I)LCT(cbz2phen) to the luminescence is observed. The photophysics of these Re(I) compounds reported herein provide new insights into the understanding of substitutional groups on the polypyridyl ligands that are relevant to practical and fundamental development of photo-induced molecular devices. (AU)

• FAPESP's process: 15/21110-4 - Exploiting Photocatalyzed Reactions Under Continuous Flow Conditions by using Porphyrinoid Systems: (C-FlowPhotoChem)
• Grantee: Kleber Thiago de Oliveira
• Support Opportunities: Regular Research Grants
• FAPESP's process: 11/23408-0 - Syntheses, characterization and photophysical investigation of rhenium (I) complexes
• Grantee: Karina Passalacqua Morelli Frin
• Support Opportunities: Regular Research Grants
• FAPESP's process: 12/24096-4 - Tetrabromobacteriochlorins in Cross-Coupling Reactions: Approaches for the Synthesis of Highly Conjugated Systems
• Grantee: Francisco Fávaro de Assis
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 13/06532-4 - Cross-coupling reactions on the synthesis of new photosensitizers with high conjugation
• Grantee: Kleber Thiago de Oliveira
• Support Opportunities: Regular Research Grants
• FAPESP's process: 15/13149-8 - Polypyridynic rhenium(I) complexes: syntheses, investigation of photophysical properties and application as luminescent probes and/or therapeutic agents
• Grantee: Karina Passalacqua Morelli Frin
• Support Opportunities: Regular Research Grants