Supramolecular Tetrad of Subphthalocyanine–Triphenylamine–Zinc Porphyrin Coordinated to Fullerene as an “Antenna‐Reaction‐Center” Mimic: Formation of a Long‐Lived Charge‐Separated State in Nonpolar Solvent

Abstract

We report here the formation of a long-lived charge-separated state of a self-assembled donor-acceptor tetrad, formed by axial coordination of a fulleropyrrolidine appended with an imidazole coordinating ligand (C(60)Im) to the zinc center of a subphthalocyanine-triphenylamine-zinc porphyrin (SubPc-TPA-ZnP), as a charge-stabilizing antenna reaction center mimic in toluene. The subphthalocyanine and triphenylamine entities, with their high-energy singlet states, act as an energy-transferring antenna unit to produce a singlet zinc porphyrin. The formation constant for the self-assembled tetrad was determined to be 1.0 x 10(4) M(-1), suggesting a moderately stable complex formation. The geometric and electronic structures of the covalently linked SubPc-TPA-ZnP triad and self-assembled SubPc-TPA-ZnP:C(60)Im tetrad were examined by using an ab initio B3LYP/6-31G method. The majority of the highest occupied frontier molecular orbital was found over the ZnP and TPA entities, whereas the lowest unoccupied molecular orbital was located over the fullerene entity, suggesting the formation of the radical-ion pair (SubPc-TPA-ZnP(*+):C(60)Im(*-)). The redox measurements revealed that the energy level of the radical-ion pair in toluene is located lower than that of the singlet and triplet states of the zinc porphyrin and fullerene entities. The femtosecond transient absorption measurements revealed fast charge separation from the singlet porphyrin to the coordinated C(60)Im with a lifetime of 1.1 ns. Interestingly, slow charge recombination (1.6 x 10(5) s(-1)) and the long lifetime of the charge-separated state (6.6 micros) were obtained in toluene by utilizing the nanosecond transient measurements.

Photosynthetic Antenna–Reaction Center Mimicry by Using Boron Dipyrromethene Sensitizers

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] In this marvelous process, sunlight is harvested by the antenna complexes and the excitation energy is funneled to the reaction center (RC), where multistep electron-transfer reactions occur to generate a potential that can drive chemical reactions ( Figure 1). [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] In this marvelous process, sunlight is harvested by the antenna complexes and the excitation energy is funneled to the reaction center (RC), where multistep electron-transfer reactions occur to generate a potential that can drive chemical reactions ( Figure 1).…”

“…There has been considerable interest in mimicking photosynthesis by means of artificial photosynthetic models. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] In this marvelous process, sunlight is harvested by the antenna complexes and the excitation energy is funneled to the reaction center (RC), where multistep electron-transfer reactions occur to generate a potential that can drive chemical reactions ( Figure 1). Constructing chemical systems capable of fast energy-and electron-transfer reactions and slow charge recombination has been a very challenging goal for chemists over the past two decades.…”

Fullerene C60 Architectures in Materials Science

“…220,221 ZnP yields the most promising donor chromophores employed in D-A systems. Among these second electron donors, TTF and exTTF moieties, 222 boron dipyrrin derivatives, 223 subPc, 224 and triphenylamine 225 showed interesting results in terms of lifetimes of CSS generated from the photoinduced ET. Among these second electron donors, TTF and exTTF moieties, 222 boron dipyrrin derivatives, 223 subPc, 224 and triphenylamine 225 showed interesting results in terms of lifetimes of CSS generated from the photoinduced ET.…”

Unidirectional Photo-induced Charge Separation and Thermal Charge Recombination of Cofacially Aligned Donor-Acceptor System Probed by Ultrafast Visible-Pump/Mid-IR-Probe Spectroscopy

“…[1][2][3][4][5][6][7][8][9][10] The ultimate goal is to generate a long-lived CS state in which an electron donor (D) and acceptor (A) is separated by a controllable distance enough to perform a variety of chemical reactions with the driving force obtained by the CS. In the early event of natural photosynthesis, CS through protein membrane occurs via only one direction (L-branch, vide infra) between the macroscopic C 2 symmetric L-and M-branches, (L) the special pair-bacteriochlorophyll (BChl L )-bacteriopheophytin (BPheo L )-menaquinone (Q a )-ubiquinone (Q b ) and (M) the special pair-bacteriochlorophyll (BChl M )-bacteriopheophytin (BPheo M )-ubiquinone (Q b )-menaquinone (Q a ).…”