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Redox‐Responsive Molecular Switches Based on Azoterpyridine‐Bridged Ru/Os Complexes
Author(s) -
Akasaka Tetsuo,
Otsuki Joe,
Araki Koji
Publication year - 2002
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20020104)8:1<130::aid-chem130>3.0.co;2-o
Subject(s) - terpyridine , bridging ligand , chemistry , ligand (biochemistry) , intramolecular force , excited state , redox , luminescence , crystallography , photochemistry , electron transfer , electrochemistry , metal , stereochemistry , inorganic chemistry , crystal structure , materials science , electrode , biochemistry , receptor , physics , nuclear physics , optoelectronics , organic chemistry
Three new terpyridine‐based dinuclear complexes, [(tpy)Ru(azotpy)Ru(tpy)] 4+ (tpy=2,2′:6′,2″‐terpyridine, azotpy=bis[2,6‐bis(2‐pyridyl)‐4‐pyridyl]diazene), [(tpy)Os(azotpy)Os(tpy)] 4+ , and [(tpy)Ru(azotpy)Os(tpy)] 4+ were prepared and their electrochemical and photophysical properties investigated. The bridging ligand, azotpy, in these complexes is reduced at less negative potentials than the unsubstituted tpy ligand. These complexes exhibit absorption bands due to the metal‐to‐ligand charge‐transfer transitions both to the unsubstituted tpy ligand and the bridging azotpy ligand, the latter absorption being observed at the lower energy side of the former. These observations are consistent with the lower lying π* level of the azotpy ligand than that of the tpy ligand. These complexes are nonluminescent, since the excited electron is trapped in this lower lying π* level of the azotpy ligand in the excited state. Reduction of this bridging ligand by constant potential electrolysis renders the shape of absorption spectra for these complexes nearly identical to those of the parent complexes, [M(tpy) 2 ] 2+ (M=Ru, Os). In this reduced state, the homodinuclear Os complex becomes luminescent at room temperature, whereas the homodinuclear Ru complex becomes luminescent at 77 K, thus establishing their photoswitching behavior. The reduced heterodinuclear complex exhibits luminescence from the Os center, which is sensitized by the Ru center in the same molecule as evidenced by the excitation spectra. Thus, the intramolecular energy transfer can be switched on and off by the redox reaction of the bridging component.