Excited state interactions in calix[4]arene-perylene bisimide dye conjugates:: Global and target analysis of supramolecular building blocks

The photophysical properties of two supramolecular building blocks oc and oc2 consisting of a perylene bisimide chromophore substituted with either one or two calix[4]arene units in the N-imide position as well as those of the reference compound oref without calix[4]arene substituents were investigated. A complete picture of the processes taking place after photoexcitation in toluene, CH2Cl2, and benzonitrile was obtained by means of UV/vis absorption, steady state and time-resolved emission, and femtosecond transient absorption spectroscopy. It has been found that the fluorescence emission of compounds oe (Phi(fl) = 0.03 in CH2Cl2) and oc2 (Phi(fl) < 0.01 in CH2Cl2) is almost completely quenched compared with the highly emissive reference compound oref (Phi(fl) = 0.99 in CH2Cl2) because of fast electron-transfer processes from the calix[4]arene moieties to the perylene bisimide chromophore. This predominantly takes place with rate constants of k(cs) = 3 x 10(10) s(-1) (tau(cs) = 32 ps) for compound oc and kcs = 9 x 1010 s-1 (tau(cs) = 11 ps) for compound oc2 (in CH2Cl2) leading to a short-lived charge-separated state consisting of the reduced perylene bisimide unit and the oxidized calix[4]rene moiety.