Self-assembly and photoinduced electron transfer in a donor- β -cyclodextrin-acceptor supramolecular system

Abstract

Equimolar amounts of native β-cyclodextrin (β-CD), pyrene-linked adamantane (PYAD) and tert-butylpyromellitic diimide (PMDI) when dissolved in water self-assembled to form the supramolecular donor-acceptor system PYAD β-CD PMDI. The high affinity of adamantane derivatives for inclusion binding in the β-CD cavity and the propensity of PMDI to undergo rim-binding at the narrow rim of β-CD led to the formation of PYAD β-CD PMDI. The ternary complex PYAD β-CD PMDI was thoroughly characterized using various spectroscopic techniques. β-CD performs three functions in the self-assembled complex: (1) encapsulate the adamantane unit and keep the pyrene (PY) moiety above the secondary rim, (2) rim-bind PMDI and keep it at the primary rim, and (3) act as a spacer between pyrene and PMDI. Thus, the ternary complex can function as a donor-spacer-acceptor system capable of undergoing photoinduced electron transfer (PET). Upon excitation of the pyrene moiety in PYAD β-CD PMDI an electron is transferred from the excited pyrene to the PMDI ground state. Steady state and time resolved fluorescence experiments were carried out to study the PET in PYAD β-CD PMDI. Existence of the ternary system and PET processes taking place within it are further supported by laser flash photolysis experiments.