Synthesis, Structural Characterisation and Photophysics of anionic cyclometalated bis(alkynyl)(benzo[h]quinolinate)platinate(II) species

Resumen

The alkynylation of [Pt(bzq)(u-Cl)]2 (bzqH = benzo[h]quinoline) with excess of LiC≡CR in diethyl ether leads to novel (7,8- benzoquinolinate)bis(alkynyl)platinate(II) monoanionic species [Pt(bzq)(C≡CR)2]- (R = tBu 1, SiMe 3 2, Ph 3, Tol 4, C6H4CF3-4 5, C5H4N-2 6, C6H4-C≡CPh 7) which have been isolated as tetrabutylammoniun salts. The molecular X-ray structures of 3 and 6 reveal the presence of discrete anions with bond lengths and angles similar to those of related cyclometalated Pt compounds and no evidence of π-π or Pt-Pt stacking interactions. The influence of the R substituent on the photophysics of the complexes has been examined by UV-visible absorption, emission spectroscopy and cyclic voltammetry. Complexes 1-6 show a similar strong luminescence in both the solid state (structureless emission) and frozen solutions (well-resolved vibronic structures) while the emissions in solution at room temperature are red shifted (relative to the glass) and weak. For these complexes, on the basis of TD-DFT calculations which reproduce the experimental structure of anion 3, [Pt(bzq)(C≡CPh)2]-, the emissions are proposed to arise from mixed [π C≡CR/Pt d/π (bzq) → π* bzq] transitions. In contrast, complex 7 which contains the extended p-phenylethynylphenylacetylide ligand, C≡CC6H 4-C≡CPh, displays a structured emission both at 298 K and in glassy CH2Cl2 solutions. In this case the lack of a significant rigidochromism and DFT theoretical calculations support the involvement of a low-lying, metal perturbed acetylenic 3ππ * (C≡CC6H4-C≡CPh) excited state. © The Royal Society of Chemistry 2003.