We are investigating intramolecular electron transfers in rhenium (I) coordination compounds. To investigate these photo-sensitive intramolecular electron transfers, we have proposed three covalently linked donor ligand acceptor complexes have been proposed with the general formula: [dmbRe(CO)₃-μ-L-μ-Re(CO)₃deb]2+, where L=1,2-bis(4-pyridyl)ethane (bpa), trans-1,2-bis(4-pyridyl)ethylene (t-bpe), and cis-1,2-bis(4-pyridyl)ethylene (c-bpe). The donor substituent is a rhenium dimethyl polypyridyl linked through a bridging ligand to an acceptor rhenium diester polypyridyl. To investigate the three proposed D-L-A complexes, we have broken them down into six intermediate complexes consisting of the donor or acceptor ligand attached to the rhenium (I) center and one of the three bridging ligands. The donor and acceptor complexes with the trans-bpe ligand exhibit nonradiative relaxation, as the intraligand (IL) band is lower in energy than the metal-to-ligand charge transfer (MLCT) band. In the trans conformation, there is less distortion in the double bond than the cis conformation, which decreases the energy of the IL band. Due to this increased distortion, the cis-bpe complexes have the MLCT band as the lowest energy band in the excited state, causing luminescence. In the bpa complexes, the conjugated pi-system is broken, which will not allow electron communication from the donor substituent to the acceptor substituent. To monitor these photo-sensitive intramolecular electron transfers, we are working on synthesizing the three full D-L-A complexes as well as analyzing them through UV-Visible Spectroscopy, Fluorescence Spectroscopy, and NMR analysis for characterization.
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