Spectroscopic and theoretical insights on supramolecular complexation of C60 and C70 with a designed bisporphyrin.

The present paper reports the synthesis of a designed bisporphyrin (1), and its supramolecular complexes with C(60) and C(70) in toluene medium. Ground state non-covalent interaction between fullerenes and 1 is evidenced from absorption spectrophotometric study in which it is observed that the intensity of the Soret absorption band of 1 decreases considerably in presence of both C(60) and C(70). Jobs plot of continuous variation method establishes 1:1 stoichiometry for fullerene/1 complexes. Steady state fluorescence studies reveal efficient quenching of fluorescence of 1 in presence of fullerenes. The Stern-Volmer diffusion constant for the supramolecular complexes of 1 with C(60) and C(70) is determined to be 1450 and 12,485 dm(3) mol(-1). The binding constants of the C(60)/1 and C(70)/1 complexes are estimated to be 12,500 and 17,200 dm(3) mol(-1), respectively. Time-resolved emission studies establish relatively long-lived charge separated state for the C(70)/1 complex. Transient absorption spectral analysis reveals formation of radical anion species, i.e., C(60)(-) and C(70)(-) Molecular mechanics calculations at force field model in vacuo evoke the stereoscopic structures of the fullerene/1 complexes and interpret the stability difference between C(60) and C(70) complexes of 1 in terms of heat of formation values.