Structural basis for vapoluminescent organoplatinum materials derived from noncovalent interactions as recognition components

The spectroscopic properties and crystal structures of a series of platinum(II) complexes bearing functionalized sigma-alkynyl groups, namely [(tBu(2)bpy)Pt(CdropCAr)(2)] (tBu(2)bpy = 4,4'-bis-tert-butyl-2,2'-bipyridine, Ar = 4-pyridyl, 1; 3-pyridyl, 2; 2-pyridyl, 3; 4-ethynylpyridyl, 4; 2-thienyl, 5; pentafluorophenyl, 6) have been studied. Solid-state emissions of 1 and 6 are dependent on their crystallinity. Reversible and selective vapoluminescence was observed for 1 and 6 in the presence of chlorocarbon vapors. For solid 1, dramatic enhancement of green luminescence is observed upon sorption of CH2Cl2 or CHCl3 vapor. The excimeric orange emission for solid 6 is switched to monomeric green emission upon exposure to CH2Cl2 vapor. The luminescent responses of a thin film of 1 towards various organic vapors have also been examined. In the crystallographically determined structure of 1(.)CH(2)Cl(2), the bis(acetylide) moiety acts as the receptor berth for a CH2Cl2 molecule through concerted C-H...pi(C=C) interactions, while Cl...Cl interactions connect the CH2Cl2 molecules into infinite linear chains. The observed crystal lattices are arranged into scaffolds of varying porosity by weak CH...N(py) (1-CH2Cl2, 1(.)CH(3)CN, 4(.)DMF) and C-H... F-C (6, 6-CH3CN) interactions. The correlation between the crystal structures of 1-CH2Cl2, 1-CH3CN, 2, 4-DMF, 5, 6, and 6-CH3CN and their vapoluminescence suggests that weak nonconventional hydrogen-bonding interactions preside over the reversible sensing and signalling processes.