Photoinduced Interactions in a Pyrene-Calix[4]arene-Perylene Bisimide Dye System: Probing Ground-State Conformations with Excited-State Dynamics of Charge Separation and Recombination

Abstract

A calix[4]arene scaffold has been functionalized with an electron-accepting perylene bisimide as well as an electron-donating pyrene unit. Steady-state and time-resolved spectroscopy indicate a strong charge-transfer (CT) interaction between these two units in all investigated solvents. The signatures of the radical anion of the perylene bisimide and the radical cation of the pyrene are observed with femtosecond transient absorption spectroscopy. A preferential π-stacked conformation is inferred. In tetrahydrofuran as a solvent ∼25% of an extended form is invoked. The CT states of these two ground-state populations (π-stacked and extended) have different formation and decay kinetics and result in the spectral distinction of a compact and an extended charge-transfer state upon visible excitation. In the extended conformation, upon UV excitation, pyrene acts as an electron acceptor that is reduced through a photoinduced electron-transfer process by the calix[4]arene. In this conformation the calixarene scaffold is accordingly not an uninvolved linker unit but participates effectively in the electron-transfer processes.