Journal of Physical Chemistry A, Vol.115, No.35, 9929-9940, 2011
New Photophysical Insights in Noncovalent Interaction between Fulleropyrrolidine and a Series of Zincphthalocyanines
The present article reports, for the first time, the photophysical aspects of noncovalent interaction of a fullerene derivative, namely, C-60 pyrrolidine tris-acid ethyl ester (PyC60) with a series of zincphthalocyanines, for example, underivatized zincphthalocyanine (1), zinc-1,4,8,11,15,18,22, 25-octabutoxy-29H,31H-phthalocyanine (2), and zinc-2,3,9,10,16,17,23,24-octakis-(octyloxy)-29H, 31H-phthalocyanine (3) in toluene. Ground state electronic interaction of PyC60 with 1, 2 and 3 has been evidenced from the observation of well-defined charge transfer (CT) absorption bands in the visible region. Utilizing the CT transition energy, vertical electron affinity (E-A(v)) of PyC60 is determined. Steady state fluorescence experiment enables us to determine the value of binding constant (K) in the magnitude of 2.60 x 10(4) dm(3).mol(-1), 2.20 x 10(4) dm(3).mol(-1), and 1.27 x 10(4) dm(3).mol(-1) for the noncovalent complexes of PyC60 with 1, 2, and 3, respectively. K values of PyC60-ZnPc complexes suggest that PyC60 is incapable of discriminating between 1, 2, and 3 in solution. Lifetime experiment signifies the importance of static quenching phenomenon for our presently investigated supramolecules and it yields larger magnitude of charge separated rate constant for the PyC60-1 species in toluene. Photoinduced energy transfer between PyC60 and ZnPc derivatives, namely, 1, 2, and 3, in toluene, has been evidenced with nanosecond laser photolysis method by observing the transient absorption bands in the visible region; transient absorption studies establish that energy transfer from (PyC60)-Py-T* to the ZnPc occurs predominantly, as confirmed by the consecutive appearance of the triplet states of PyC60. Theoretical calculations at semiempirical level (PM3) evoke the single projection geometric structures for the PyC60-ZnPc systems in vacuo, which also proves that interaction between PyC60 and ZnPc is governed by the electrostatic mechanism rather than dispersive forces associated with pi-pi interaction.