Electron Transfer in the Supramolecular Donor−Acceptor Dyad of Zinc Porphycene

Abstract

The electron transfer processes of Zn octaethylporphycene (ZnPcn), a structural isomer of Zn octaethylporphyrin, have been investigated mainly using transient absorption spectroscopy. To form a supramolecular donor-acceptor dyad, imide compounds bearing a pyridine group at the N position of the imides have been used as an acceptor. The N atom of the pyridine ring can coordinate to the central Zn ion of ZnPcn. Formation of a supramolecular donor-acceptor dyad, that is, pentacoordinated ZnPcn, was confirmed by steady-state absorption spectroscopy using toluene as a solvent. Charge separation upon excitation of ZnPcn was indicated by efficient fluorescence quenching, especially when pyromellitic diimide was used as the acceptor. Electron transfer processes were confirmed by subpicosecond transient absorption spectroscopy, in which generation of a radical anion of the acceptor and a radical cation of ZnPcn, which was identified by means of gamma-ray radiolysis, was confirmed. It became clear that the charge separation rate was smaller than that of the corresponding supramolecular dyads of Zn tetraphenylporphyrin and Zn octaethylporphyrin despite a similar driving force. This observation indicates a larger internal reorganization energy and a smaller coupling element of the ZnPcn dyad.

Photoinduced Electron Transfer of Porphyrin Isomers: Impact of Molecular Structures on Electron‐Transfer Dynamics

“…With an increase in the delay time, absorption bands at 720 and 890 nm became apparent, which can be attributed to the radical anion of PI and the radical cation of ZnOEPcn, respectively, which indicates the intramolecular charge separation (CS) from the singlet excited ZnOEPcn. Similar CS and CR processes were confirmed with other dyads …”

“…The absorption spectra of radical cations of Zn II ‐incorporated OEPcn, OHPcn, and OECn were reported by our groups employing γ‐ray radiolysis of the 77 K n ‐butylchloride matrix . The radical cations of ZnOEPcn, ZnOHPc, and ZnOEcn showed clear peaks at 860, 756, and 705 nm, respectively (Figure ).…”

“…To clarify the characteristics of the porphyrin isomers in the ET processes, parameters, such as the reorganization energy and electronic coupling, have to be compared. For this purpose, we systematically investigated the ET processes in the donor–acceptor supramolecular dyads, in which isomers of ZnOEP, that is, ZnOEPcn, ZnOEHPcn, and ZnOECn, were used as the donor . As an electron acceptor, derivatives of pyromellitic imide and phthalimide bearing a pyridine ring for ligation to Zn ion were employed (Scheme ).…”

“…Data is taken from Ref. . Reprinted with permission from American Chemical Society (Copyright (2009, 2010)), Elsevier (Copyright (2011)), and the PCCP Owner Society.…”

Supramolecular Inclusion Complexes of Two Cyclic Zinc Bisporphyrins with C60 and C70: Structural, Thermodynamic, and Photophysical Characterization

“…[50] The CS state energy levels should be taken only as approximate values, because the application of the Weller formula has been shown to have several limitations. [51][52][53] We can, however, safely assume that the CS state is below the level of all excited states, including triplets. In the present case the energy levels of the various complexes, C 60 @2·Zn 2 , C 70 @2·Zn 2 , and C 70 @1·Zn 2 , are essentially identical in the same solvent, and a single energy level scheme can be used to describe the generic M-Ful inclusion complex made by a Zn porphyrinic macrocycle (M) with a fullerene (Ful).…”