Photophysics of [Pt{4-(o-tolyl)isqbipy}Cl]SbF6, where 4-(o-Tolyl)isqbipy is the New 4-(o-Tolyl)-6-(3´´ -isoquinolyl)-2,2´-bipyridyl Ligand

Abstract

The synthesis and characterisation of the 4-(o-tolyl)-6-(3′′-isoquinolyl)-2,2′-bipyridyl [4-(o-tolyl)isqbipy] ligand is described. A single-crystal X-ray structure determination shows that it adoptsatrans-transconformation about the interannular bonds linking the central pyridine ring to theouter pyridine ring and the isoquinolyl moiety. Theo-tolyl group is twisted by an angle of 51.7◦out of the plane of the central pyridine ring. The synthesis and characterisation of the [Pt{4-(o-tolyl)isqbipy}Cl]SbF6complex is described. The absorption spectrum of the complex measured inacetonitrile exhibits MLCT bands at 362 and 393 nm, as well as intraligandπ-π∗absorptions inthe 200 – 350 nm range; the MLCT bands are shifted significantly to higher energy when com-pared to those recorded for the parent trpy complex,viz.[Pt{4′-(o-tolyl)trpy}Cl]SbF6,wheretrpyis 2,2′:6′,2′′-terpyridine. Similarly, the3MLCT emission measured for the 4-(o-tolyl)isqbipy com-plex in a 1 : 1 CH2Cl2/CHCl3solution is blue-shifted with respect to the emission spectrum recordedfor the 4′-(o-tolyl)trpy complex. We attribute the higher energy MLCT absorption and emission forthe 4-(o-tolyl)isqbipy complex to a significantly higher energy for itsπ∗-LUMO than for that ofthe 4′-(o-tolyl)trpy complex. Emission spectra of the title compound have also been measured in alow-temperature 1 : 5 : 5 (v/v) DMF/methanol/ethanol (DME) glass as a function of concentration.These spectra show that aggregation of the complex occurs at rather low concentrations of 5 – 10μM,probably to dimers. Variable-temperature emission spectra recorded on a solid sample of [Pt{4-(o-tolyl)isqbipy}Cl]SbF6comprise relatively narrow asymmetric bands whose maxima are shifted to thered as the temperature is lowered: specificallyλem(max) is 641 nm at r. t. (τ= 235 ns) and 676 nm at77 K (τ=1.36μs). Temperature-dependent emission of this type is typical of a metal-metal-to-ligandcharge transfer (MMLCT) excited state that has its origin indz2(Pt)-dz2(Pt) orbital interactions in thecrystal