Molecular assembly of PC70BM with a designed monoporphyrin: Spectroscopic investigation in solution and theoretical calculations

Abstract The present paper reports a detailed photophysical investigation on the supramolecular interactions of a functionalised fullerene, namely [6,6]-phenyl C 71 butyric acid methyl ester (PC 70 BM), with a designed monoporphyrin, [bis(4-hydroxyseselinyl)porphyrin] ( 1 ), in toluene and 1,2-dichlorobenzene (DCB). The values of the binding constant ( K ) for the PC 70 BM- 1 system measured by steady-state fluorescence investigation in toluene ( K PCBM- 1 (toluene)) and DCB ( K PCBM- 1 (DCB)) are estimated to be 15,085 dm 3  mol −1 and 6700 dm 3  mol −1 , respectively. A moderate value of selectivity ( K ) is observed for the PC 70 BM- 1 system in toluene and DCB ( K PC70BM- 1 (Toluene) / K PC70BM- 1 (DCB) ~2.25) due to a solvophobic effect. Life time measurements proved that photo-excited 1 ⁎ undergoes decay in the presence of PC 70 BM in toluene and DCB as a result of static quenching. Hybrid-density functional theory (DFT) calculations predicted the geometric structure of PC 70 BM- 1 system in vacuo and established the electronic redistribution between PC 70 BM and 1 in the PC 70 BM- 1 system with the help of molecular orbital, molecular electrostatic potential map, and multipole bond moment calculations. Transient-absorption measurements established that binding interactions overcome both energy and/or electron-transfer process(es) during non-covalent interactions between PC 70 BM and 1 in solution.