Axially assembled photosynthetic reaction center mimics composed of tetrathiafulvalene, aluminum(III) porphyrin and fullerene entities

作者：Poddutoori Prashanth K^*; Lim Gary N; Sandanayaka Atula S D; Karr Paul A; Ito Osamu; D'Souza Francis; Pilkington Melanie; van der Est Art

来源：Nanoscale, 2015, 7(28): 12151-12165.

DOI：10.1039/c5nr01675d

The distance dependence of sequential electron transfer has been studied in six, vertical, linear supramolecular triads, (TTF-Ph-n-py -> AlPor-Ph-m-C-60, n = 0, 1 and m = 1, 2, 3), constructed using tetrathiafulvalene (TTF), aluminum(III) porphyrin (AlPor) and fullerene (C-60) entities. The C-60 and TTF units are bound to the Al center on opposite faces of the porphyrin; the C-60 through a covalent axial bond using a benzoate spacer, and the TTF through a coordination bond via an appended pyridine. Time-resolved optical and EPR spectroscopic methods and computational studies are used to demonstrate that excitation of the porphyrin leads to step-wise, sequential electron transfer (ET) between TTF and C-60, and to study the electron transfer rates and exchange coupling between the components of the triads as a function of the bridge lengths. Femtosecond transient absorption studies show that the rates of charge separation, k(CS) are in the range of 10(9)-10(11) s(-1), depending on the length of the bridges. The lifetimes of the charge-separated state TTF center dot+-C-60(center dot-) obtained from transient absorbance experiments and the singlet lifetimes of the radical pairs obtained by time-resolved EPR are in good agreement with each other and range from 60-130 ns in the triads. The time-resolved EPR data also show that population of the triplet sublevels of the charge-separated state in the presence of a magnetic field leads to much longer lifetimes of >1 mu s. The data show that a modest stabilization of the charge separation lifetime occurs in the triads. The attenuation factor beta = 0.36 angstrom(-1) obtained from the exchange coupling values between TTF center dot+ and C-60(center dot-) is consistent with values reported in the literature for oligophenylene bridged TTF-C-60 conjugates. The singlet charge recombination lifetime shows a much weaker dependence on the distance between the donor and acceptor, suggesting that a simple superexchange model is not sufficient to describe the back reaction.

• 出版日期2015