Photoinduced processes in fullerenopyrrolidine and fullerenopyrazoline derivatives substituted with an oligophenylenevinylene moiety

Fullerene derivatives A-3PV and B-3PV in which an oligophenylenevinylene trimeric subunit (3PV) is attached to C-60 through, respectively, a pyrrolidine or a pyrazoline ring have been prepared. The electrochemical and excited-state properties Of the multicomponent arrays A-3PV and B-3PV have been investigated in Solution using the related oligophenylenevinylene derivative 3PV, fullerenopyrrolidine A and fullerenopyrazoline B as reference Compounds. In A-3PV quantitative OPV --> C-60 photoinduced singlet-singlet energy transfer has been observed. Population of the lowest fullerene singlet excited state is followed by nearly quantitative intersystem crossing to the lowest fullerene triplet excited state in CH2Cl2 and toluene. whereas OPV --> C-60 electron transfer is able to compete significantly in the more polar solvent benzonitrile. In the case of B-3PV, the excited-state properties are more complex due to the electron donating ability of the pyrazoline ring. As observed for A-3PV, quantitative OPV --> C-60 photoinduced singlet-singlet energy transfer Occurs in B-3PV. However, in this case, the population of the lowest fullerene singlet excited state is followed by an efficient electron transfer from the pyrazoline ring in CH2Cl2 and benzonitrile. In B-3PV. studies of the dependence of photoinduced processes on solvent polarity. addition of acid. and temperature also reveal that this Compound can be considered as a fullerene-based molecular switch, the switchable parameters being the photoinduced processes. Finally, A-3PV and B-3PV have been tested as active materials in photovoltaic devices and the differences of light to energy conversion efficiencies found for the two compounds have been rationalised on the basis of their photophysical properties.