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Luminescent Alkynylplatinum(II) Complexes of 2,6‐Bis( N ‐alkylbenzimidazol‐2′‐yl)pyridine‐Type Ligands with Ready Tunability of the Nature of the Emissive States by Solvent and Electronic Property Modulation
Author(s) -
Tam Anthony YiuYan,
Lam Wai Han,
Wong Keith ManChung,
Zhu Nianyong,
Yam Vivian WingWah
Publication year - 2008
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/chem.200701914
Subject(s) - luminescence , chemistry , ligand (biochemistry) , pyridine , excited state , crystallography , photochemistry , metal , absorption (acoustics) , solvent , medicinal chemistry , materials science , atomic physics , organic chemistry , optoelectronics , physics , biochemistry , receptor , composite material
A new class of luminescent alkynylplatinum(II) complexes of tridentate bis( N ‐alkylbenzimidazol‐2′‐yl)pyridines (bzimpy), [Pt(R,R′‐bzimpy)(CCR′′)]X (X=PF 6 , OTf), and one of their chloro precursor complexes, [Pt(R,R′‐bzimpy)Cl]PF 6 , have been synthesized and characterized; one of the alkynyl complexes has also been structurally characterized by X‐ray crystallography. Electrochemical studies showed that the oxidation wave is alkynyl ligand‐based in nature with some mixing of the metal center‐based contribution, whereas the two quasi‐reversible reduction couples are mainly bzimpy‐based reductions. The electronic absorption and luminescence properties of the complexes have also been investigated. In solution, the high‐energy and intense absorption bands are assigned as the π–π* intraligand (IL) transitions of the bzimpy and alkynyl ligands, whereas the low‐energy and moderately intense absorptions are assigned to an admixture of metal‐to‐ligand charge‐transfer (MLCT) (dπ(Pt)→π*(R,R′‐bzimpy)) and ligand‐to‐ligand charge‐transfer (LLCT) (π(CCR′′)→π*(R,R′‐bzimpy)) transitions. Upon variation of the electronic effects of the arylalkynyl ligands, vibronic‐structured or structureless emission bands, originating from triplet metal‐perturbed intraligand (IL) or an admixture of triplet metal‐to‐ligand charge‐transfer (MLCT) and ligand‐to‐ligand charge‐transfer (LLCT) excited states respectively, were observed in solution. Interestingly, two of the complexes showed a dual luminescence that was sensitive to the polarity of the solvents. Upon cooling from 298 K to 155 K, drastic color, UV/Vis, and luminescence changes were observed in a butyronitrile solution of 1 , and were ascribed to the formation of aggregate species through Pt⋅⋅⋅Pt and π–π stacking interactions. DFT and time‐dependent DFT (TD‐DFT) calculations have been performed to verify and elucidate the results of the electrochemical and photophysical properties.