Spectroscopic and theoretical investigations on effective and selective interaction of fullerenes C < inf > 60 < /inf > and C < inf > 70 < /inf > with a derivatized Znphthalocyanine: Stabilization of charge-recombined state by side-on approach of C < inf > 70 < /inf >

Abstract

The photophysical aspects of noncovalently linked fullerenes C60 and C70 with a designed metallophthalocyanine, namely, zinc-2,3,9,10,16,17,23,24-octakis-(octyloxy)-29H,31H-phthalocyanine (1) have been investigated employing various spectroscopic tools such as UVvis absorption spectrophotometry, steady state and time-resolved fluorescence, along with solution state IR measurements in toluene medium. The ground state interaction between fullerenes and 1 is first evidenced from UVvis measurements. Binding constants (K) for the complexes of C60 and C70 with 1 are determined to be 13 235 and 27 670 dm3·mol1, respectively. Steady state fluorescence experiment reveals efficient quenching of the excited singlet state of 1 in presence of both C60 and C 70. Emission studies reveal K values of 8945 and 19 175 dm 3·mol1 for C60/1 and C70/1 complexes, respectively. The magnitude of K suggests that 1 preferentially binds C70 in comparison to C60 as average selectivity in K of C70 over C60 is enumerated to be 2.0. Time resolved emission measurements establish that C70/1 complex is stabilized much more in comparison to C60/1 complex in terms of charge recombination. Liquid IR studies provide very good support in favor of ground state complexation between fullerenes and 1. Molecular mechanics calculations at force field model and semiempirical calculations employing third parametric method substantiate the strong binding between C70 and 1, and at the same time, determine the orientation of bound guest (here C70) within the cavity of 1. © 2010 American Chemical Society.