Photophysical investigations on effective and selective complexation of a designed monoporhyrin with C₆₀ and C₇₀ in solution.

The present paper reports spectroscopic and theoretical insights on ground state complexation of a designed monoporphyrin, 1, with C60 and C70 in toluene. The central interest of the present investigations is the selectivity in binding constant (K) of the fullerene-1 complexes in solution. The ground state interaction between fullerenes and 1 is first evidenced from UV-Vis measurements. Steady state fluorescence experiment reveals efficient quenching of the excited singlet state of 1 in presence of both C60 and C70. Average K values, viz., K(av), for the complexes of C60 and C70 with 1 are determined to be 1620 and 30330 dm(3) mol(-1), respectively. The magnitude of K(av) suggests that 1 preferentially binds C70 in comparison to C60. Time resolved emission measurements establish that C70-1 complex is stabilized much more in comparison to C60-1 system in terms of charge separation process. Ab initio calculations in vacuo substantiate the strong binding between C70 and 1 in terms of heat of formation values of the respective complex, and at the same time, determine the orientation of bound guest (here C70) with the molecular plane of 1.