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Spatial extent of the singlet and triplet excitons in luminescent angular-shaped transition-metal diynes and polyynes
Suk-Yue Poon1, Wai-Yeung Wong, Kok-Wai Cheah
1Department of Chemistry and Centre for Advanced Luminescence Materials, Hong Kong Baptist University, Waterloo Road, Kowloon Tong, Hong Kong, PR China.
Abstract:
A novel approach based on conjugation interruption has been developed and is presented for a series of luminescent and thermally stable chalcogen-bridged platinum(II) polyyne polymers trans-[{-Pt(PBu3)2C[triple bond]C(C6H4)E(C6H4)C[triple bond]C-}n] (E = O, S, SO, SO2). Particular attention was focused on the photophysical properties of these Group 10 polymetallaynes and comparison was made to their binuclear model complexes trans-[Pt(Ph)(PEt3)2C[triple bond]C(C6H4)E(C6H4)C[triple bond]CPt(Ph)(PEt3)2] and their closest Group 11 gold(I) and Group 12 mercury(II) neighbours, [MC[triple bond]C(C6H4)E(C6H4)C[triple bond]CM] (M = Au(PPh3), HgMe; E = O, S, SO, SO2). The regiochemical structures of these angular-shaped molecules were studied by NMR spectroscopy and single-crystal X-ray structural analyses. Upon photoexcitation, each one has an intense purple-blue fluorescence emission near 400 nm in dilute fluid solutions at room temperature. Harvesting of the organic triplet emissions harnessed through the strong heavy-atom effects of Group 10-12 transition metals was studied in detail. These metal-containing aryleneethynylenes spaced by chalcogen units were found to have large optical gaps and high-energy triplet states. The influence of metal- and chalcogen-based conjugation interrupters on the intersystem crossing rate and on the spatial extent of the lowest singlet and triplet excitons was fully elucidated. We discuss and compare the phosphorescence spectra of these transition-metal diynes and polyynes in terms of the nature of the metal centre, conjugated chain length and Group 16 spacer unit. Our work here indicates that high-energy triplet states in these materials intrinsically give rise to very efficient phosphorescence with fast radiative decays and one could readily observe room-temperature phosphorescence for the platinum polyynes.
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