Molecular complexation between PCBM and porphyrazine in solution: A case study of non-covalent interaction

Abstract

The present investigations report the non-covalent interaction of a fullerene derivative, namely, [6,6]-phenyl C71 butyric acid methyl ester (PC70BM) with 2,7,12,17-tetra-tert-butyl-5,10,15,20-tetraaza-21H,23H-porphine (1) and zinc-2,7,12,17-tetra-tert-butyl-5,10,15,20-tetraaza-21H,23H-porphine (2) in toluene and also in mixed solvent comprising toluene and 1,2-dichlorobenzene (volume:volume=3:2). Complex formation by steady state fluorescence studies reveal high value of binding constant (K) for both PC70BM-1 and PC70BM-2 systems in toluene, i.e., KPCBM-1=10,820dm3·mol−1 and KPCBM-2=9655dm3·mol−1, and very good selectivity of binding for 1 as a result of change in solvent polarity, viz., KPC70BM-1 (Toluene)/KPC70BM-1 (Mixed Solvent) ~3.0. Due to solvophobic effect, the selectivity in binding for 2 in two different solvents, i.e., KPC70BM-2 (Toluene)/KPC70BM-2 (Mixed Solvent) estimated to be ~1.0. Lifetime measurements establish that static quenching mechanism is operative behind the photoexcited decay of 1⁎ (and/2⁎) in presence of PC70BM both in toluene and in mixed solvent. However, in mixed solvent, PC70BM-1 system is found to exhibit much higher value of magnitude of rate constant of charge-separation (i.e., kCSs(PC70BM-1)=2.97×107s−1) and kCSs(PC70BM-2)=5.60×106s−1) and quantum yield of charge-separation (ϕCS(PC70BM-1)=0.070) compared to PC70BM-2 system (ϕCS(PC70BM-1)=0.015). Ab initio calculations in vacuo predict the geometric structures of PC70BM-1 and PC70BM-2 systems and provide very good support in favour of charge-separation in former system in terms of multipole moment calculations.