bacteriochlorin and zinc-hematoporphyrin

Self-aggregates of a synthetic zinc porphyrin worked as a light absorber and photoexcited energy donor, transferred the collected energy to a small amount of 3-acetyl-(bacterio)chlorin monomer, and induced near-infrared fluorescence from the acceptors in aqueous micellar solution. These artificial supramolecular systems are novel models of the main light-harvesting antennas of green photosynthetic bacteria, chlorosomes.

Topics: Bacteria; Energy Transfer; Light-Harvesting Protein Complexes; Metalloporphyrins; Models, Biological; Porphyrins; Spectrometry, Fluorescence

The efficiencies of organic solar cells that incorporate light-harvesting arrays of organic pigments were calculated under 1 sun of air mass 1.5 solar irradiation. In one set of calculations, photocurrent efficiencies were evaluated for porphyrin, phthalocyanine, chlorin, bacteriochlorin, and porphyrin-bis(perylene) pigment arrays of different length and packing densities under the assumption that each solar photon absorbed quantitatively yielded one electron in the external circuit. In another more realistic set of calculations, solar conversion efficiencies were evaluated for arrays comprising porphyrins or porphyrin-(perylene)2 units taking into account competitive excited-state relaxation pathways. A system of coupled differential equations for all reactions in the arrays was solved on the basis of previously published rate constants for (1) energy transfer between the perylene and porphyrin pigments, (2) excited-state relaxation of the perylene and porphyrin pigments, and (3) excited-state electron injection into the semiconductor. This formal analysis enables determination of the optimal number of pigments in an array for solar-to-electrical energy conversion. The optimal number of pigments depends on the molar absorption coefficient and the density at which the arrays can be packed on an electrode surface. Taken together, the ability to employ fundamental photophysical, kinetic, and structural parameters of modular molecular architectures in assessments of the efficiency of solar-to-electrical energy conversion should facilitate the design of molecular-based solar cells.

Topics: Electrons; Energy Transfer; Indoles; Isoindoles; Kinetics; Light; Metalloporphyrins; Models, Chemical; Molecular Structure; Perylene; Photochemistry; Porphyrins; Semiconductors; Sensitivity and Specificity; Spectrum Analysis; Surface Properties

It is well-known that time-dependent density functional theory (TDDFT) yields substantial errors for the excitation energies of charge-transfer (CT) excited states, when approximate standard exchange-correlation (xc) functionals are used, for example, SVWN, BLYP, or B3LYP. Also, the correct 1/R asymptotic behavior of CT states with respect to a distance coordinate R between the separated charges of the CT state is not reproduced by TDDFT employing these xc-functionals. Here, we demonstrate by analysis of the TDDFT equations that the first failure is due to the self-interaction error in the orbital energies from the ground-state DFT calculation, while the latter is a similar self-interaction error in TDDFT arising through the electron transfer in the CT state. Possible correction schemes, such as inclusion of exact Hartree-Fock or exact Kohn-Sham exchange, as well as aspects of the exact xc-functional are discussed in this context. Furthermore, a practical approach is proposed which combines the benefits of TDDFT and configuration interaction singles (CIS) and which does not suffer from electron-transfer self-interaction. The latter approach is applied to a (1,4)-phenylene-linked zincbacteriochlorin-bacteriochlorin complex and to a bacteriochlorophyll-spheroidene complex, in which CT states may play important roles in energy and electron-transfer processes. The errors of TDDFT alone for the CT states are demonstrated, and reasonable estimates for the true excitation energies of these states are given.

Topics: Bacteriochlorophylls; Carotenoids; Electron Transport; Energy Transfer; Metalloporphyrins; Models, Chemical; Photosynthetic Reaction Center Complex Proteins; Porphyrins; Proteobacteria; Systems Theory; Time Factors