title: Shape-persistent (Pt-salphen)2 phosphorescent coordination frameworks: structural insights and selective perturbations.
abstract: The development of molecular frameworks derived from binuclear platinum(II) aromatic Schiff base (salphen) complexes and their supramolecular chemistry have been undertaken. A series of axially rotating (Pt-salphen)2 luminophores, tethered in a cofacial manner by a rigid linker (xanthene, 1; dibenzofuran, 2; biphenylene, 3), was synthesized in which the O(salphen) groups are potentially amenable for guest-binding. The molecular structures of 1 and 3 have been determined by X-ray crystallography, revealing intra- and intermolecular π-stacking interactions, as well as contrasting syn (1) and anti (3) configurations, for the (Pt-salphen)2 moiety. All complexes are luminescent in solution at room temperature. Their photophysical and solvatochromic properties have been examined, and the emissions are assigned to mixed triplet O(p)/Pt(d)→π*(diimine) excited states. The red-shifted fluid emissions and lower quantum yields of 1 and 3, relative to 2, are ascribed to enhanced intramolecular π-stacking interactions. Photophysical changes and selective responses to metal ions (particularly Pb(2+)) have been investigated by using various spectroscopic methods and DFT calculations, and through comparative studies with control complexes. A plausible binding mechanism is proposed based on occupation of the O(salphen)-binding cavity, which induces perturbation of intramolecular π-π interactions, and hence the self-quenching and emission properties, of the (Pt-salphen)2 unit.
authors.affiliation: Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, P.R. China.
authors.forename: Zhengqing
authors.initials: Z
authors.lastname: Guo
authors.forename: Shek-Man
authors.initials: SM
authors.lastname: Yiu
authors.forename: Michael C W
authors.initials: MC
authors.lastname: Chan