Long-range Through-space Charge Transfer in a pH-responsive Mixed Cyclophane of Pyridine and Teropyrene

A large, strained (SE=44.2 kcal/mol) and conformationally flexible mixed cyclophane of pyridine and teropyrene was synthesized using two intramolecular Wurtz coupling reactions and an unprecedented Scholl reaction between the unreactive 2 positions of the pyrene systems in a triply bridged pyrenophane. Protonation of the pyridine unit results in a greatly enhanced preference for nesting in the cavity of the highly bent teropyrene system (theta(calc)=162.6 degrees) and emergence of a charge transfer absorption band (lambda(max)=592 nm) due to a long range (5.0-5.5 & Aring;), through-space intramolecular transition between the teropyrene and pyridinium units, which does not exist in the neutral cyclophane.