"Extra stabilisation" of a pyrene based molecular couple by γ-cyclodextrin in the excited electronic state

Two thiosemicarbazide and semicarbazide functionalized pyrene labeled Schiff base compounds have been synthesized. The pyrene moieties in the compounds result in formation of π-π coupled complexes in aqueous medium in the excited electronic state. Added γ-cyclodextrin allows incorporation of the pyrene head inside its less polar core and promotes hydrogen bonding of the thio and oxo groups of the compounds with its rim hydroxyl groups to "stabilise" the monomers. This is confirmed by FT-IR and absorption spectroscopy. The stabilised monomers lead to formation of stabilised excimers as monitored by steady state and time-resolved fluorescence spectroscopy through varying the experimental conditions. The proposed model for the stabilisation of the Schiff base monomers has been evidenced by comparing with the fluorescence spectroscopic changes of two control compounds. The present work reports a step ahead toward proposing a simple host-guest method to extra stabilise the pyrene based excimers that can be biologically utilised.