Effect of Anion Ligation on Electron Transfer of Double-Linked Zinc Porphyrin−Fullerene Dyad

Abstract

The interaction between metalloporphyrins and their axial ligands plays an important role in the electron transfer (ET) processes in which the excited porphyrin participates. An efficient photoinduced ET reaction of a double-linked zinc(II) porphyrin-fullerene dyad was demonstrated in ionic environment. The chloride ion of tetrabutylammonium chloride (TBACl) electrolyte solution ligates the zinc porphyrin moiety in the dyad which results in a red shift of the absorption bands and lowers the energy of the charge-separated state by about 0.26 eV as compared to the nonligated dyad. Excitation of the porphyrin chromophore results in ET from porphyrin to fullerene in a moderately polar solvent, anisole. In nonionic and nonligating ionic environments, the ET reaction occurs through an intermediate state, an intramolecular exciplex, which has emission in the near-infrared region of the spectrum. This emission is not observed directly for the dyad in TBACl/anisole solution, but evidence of the exciplex intermediate was seen in the time-resolved measurements. The lower energy of the charge-separated state in the ligated environment explains the different ET reaction rates determined in the spectroscopic studies: the charge recombination process of the ligated dyad is about 5 times faster than that of the nonligated one.

Quantitative Analysis of Intramolecular Exciplex and Electron Transfer in a Double-Linked Zinc Porphyrin–Fullerene Dyad

“…The long-lived component has contributions of both the exciplex and the CCS state; i.e., it can be attributed to a mixture between the two states. 34 The trend is that the decrease in the solvent polarity results in an increase of both lifetimes, a decrease in intensity of the short-lived component, and a slight difference in the shape of the longlived component (Figures 3 and 4).…”

“…In toluene/anisole, anisole, and DCB a biexponential fits were required (see spectra in anisole as an example in Figure ), but the relative amplitude of the fast component is weaker than that observed in more polar solvents, i.e., anisole/PhCN, PhCN, and DMF (Figure ). The long-lived component has contributions of both the exciplex and the CCS state; i.e., it can be attributed to a mixture between the two states . The trend is that the decrease in the solvent polarity results in an increase of both lifetimes, a decrease in intensity of the short-lived component, and a slight difference in the shape of the long-lived component (Figures and ).…”

Excited States of Light-Harvesting Systems Based on Fullerene/Graphene Oxide and Porphyrin/Smaragdyrin

“…The combination of porphyrins and fullerenes is one of the most extensively organic donor–acceptor pairs studied − as also the assemblies are formed by porphyrins and graphene for light-harvesting and photo catalysis. − However, to our best knowledge, complexes containing smaragdyrin and nanocarbon structures like graphene or fullerene have not been reported.…”

Can MP(P)4 Compounds Form Complexes with C60?

“…Also, formation of such supramolecular assemblies has been shown to occur due to metal−ligand bonds [12,13], hydrogen bonds [14][15][16], electrostatic interactions [17], mechanical bonds [18,19], or a combination of several of these interactions [20][21][22]. The assemblies of porphyrins and fullerenes are considered as one of the most extensively organic donor−acceptor pairs studied [23][24][25][26][27][28][29][30][31][32][33][34]. So far, numerous complexes between versatile derivatives of metalloporphyrins MP (with M = Mn, Co, Ni, Cu, Zn, and Fe) or a free porphyrin and C 60 have been synthesized and characterized .…”