Photosynthetic Reaction Center Mimicry: Low Reorganization Energy Driven Charge Stabilization in Self-Assembled Cofacial Zinc Phthalocyanine Dimer−Fullerene Conjugate

Absorption spectrophotometric, fluorescence, transient absorption and quantum chemical investigations on fullerene/phthalocyanine supramolecular complexes

The present paper reports the photophysical investigations on supramolecular interaction of a phthalocyanine derivative, namely, 2,9,16,23-tetra-tert-butyl-29H,31H-Pc (1) with C(60) and C(70) in toluene. The binding constants of the C(60) and C(70) complexes of 1 are estimated to be 27,360 and 25,205 dm(3), respectively. Transient absorption measurements in the visible region establishes that energy transfer from C60*T (and C70*T) to 1 occurs predominantly in toluene which is subsequently confirmed by the consecutive appearance of the triplet states of 1. Quantum chemical calculations at DFT level of theory explore the geometry and electronic structure of the supramolecules and testify the significant redistribution of charge between fullerenes and 1.

Supramolecular organization of light-harvesting porphyrin macrorings

Porphyrin-based supramolecular nanostructures have been produced by the self-assembly of porphyrin macrorings with three benzoic acid groups (Acid-R) on each side of the rings through cooperative carboxyl-carboxyl hydrogen bonds. Structures of the organized Acid-R were analyzed by AFM, and two clear distribution peaks were observed at 3 and 27 nm in the height-distribution histogram. From the overall assessment, the higher objects are considered to be one-dimensional structures standing vertically on the mica substrate. The height corresponds to an 11-mer of a unit Acid-R. Light-harvesting functions were examined by using fluorescence titration, whereby an energy-acceptor molecule (Tripod 2) was employed that strongly interacted with Acid-R units (association constant: 2.0×10(8)  M(-1) ), specifically from the inner pore. The titration results showed that the apparent stoichiometry [Tripod 2]/[Acid-R] was <0.5, and that the value was concentration dependent. Titration results reasonably account for the scheme in which Tripod 2 only interacts with each terminal in the organized Acid-R. The number of organization was fitted to a 10-mer of Acid-R in a 6.8×10(-7)  M solution, and was consistent with that estimated from the AFM results. In the composites of organized Acid-R/Tripod 2, a singlet excitation energy transfer occurred among the Acid-R units, and to Tripod 2. The energy-transfer rate constants were estimated by using the decamer model, which employed kinetic parameters obtained from steady-state and time-resolved fluorescence experiments.

Multistep electron transfer systems based on silicon phthalocyanine, [60]fullerene and trinitrofluorenone

The synthesis and photodynamics in the absence and in the presence of Mg(2+) ions of a novel TNF-C(60)-SiPc-C(60)-TNF pentad are reported. The redox gradient approach allows to obtain a long-lived CS state of 160 ns and 200 micros in the absence and in the presence of Mg(2+) ions, respectively.