UV–vis spectrophotometric and theoretical investigations on charge transfer complexes of a designed mesotetraphenylporphyrin with C60 and C70

The present investigations report the UV–vis absorption studies on electron donor–acceptor (EDA) complexes of 5,10,15,20-tetrakis(octadecyloxyphenyl)-21H,23H-porphyrin (TP) with C60, C70 and some other electron acceptors in chloroform medium. Charge transfer (CT) absorption bands of the above mentioned complexes have been located in the visible region and vertical ionization potential of TP has been determined from the trend in CT transition energy. CT is very weak in these complexes as revealed from very low value of oscillator and transition dipole strengths. All the complexes are found to stable with 1:1 stoichiometry. Binding constants (K) for the fullerene complexes of TP are determined at four different temperatures from which enthalpies and entropies of binding of the processes have been estimated. The high K value for the C70/TP complex as well as C70/C60 selectivity ratio at room temperature supports the understanding of EDA complex binding between fullerenes and porphyrin. Ab initio theoretical investigations provide a rational support in favor of strong complexation between C70 and TP.