Photoinduced intra- and intermolecular electron transfer in solutions and in solid organized molecular assemblies

Abstract

The present paper highlights results of a systematic study of photoinduced electron transfer, where the fundamental aspects of the photochemistry occurring in solutions and in artificially or self-assembled molecular systems are combined and compared. In photochemical electron transfer (ET) reactions in solutions the electron donor, D, and acceptor, A, have to be or to diffuse to a short distance, which requires a high concentration of quencher molecules and/or long lifetimes of the excited donor or acceptor, which cannot always be arranged. The problem can partly be avoided by linking the donor and acceptor moieties covalently by a single bond, molecular chain or chains, or rigid bridge, forming D-A dyads. The covalent combination of porphyrin or phthalocyanine donors with an efficient electron acceptor, e.g. fullerene, has a two-fold effect on the electron transfer properties. Firstly, the electronic systems of the D-A pair result in a formation of an exciplex intermediate upon excitation both in solutions and in solid phases. The formation of the exciplex accelerates the ET rate, which was found to be as fast as >10(12) s(-1). Secondly, the total reorganization energy can be as small as 0.3 eV, even in polar solvents, which allows nanosecond lifetimes for the charge separated (CS) state. Molecular assemblies can form solid heterogeneous, but organized systems, e.g. molecular layers. This results in more complex charge separation and recombination dynamics. A distinct feature of the ET in organized assemblies is intermolecular interactions, which open a possibility for a charge migration both in the acceptor and in the donor layers, after the primary intramolecular exciplex formation and charge separation in the D-A dyad. The intramolecular ET is fast (35 ps) and efficient, but the formed interlayer CS states have lifetimes in microsecond or even second time domain. This is an important result considering possible applications.

Photocatalytic Hydrogen Evolution Based on Efficient Energy and Electron Transfers in Donor–Bridge–Acceptor Multibranched‐Porphyrin‐Functionalized Platinum Nanocomposites

“…Over the last four decades, photocatalytic hydrogen evolution has been studied extensively for the development of renewable energy technologies because of the depletion of fossil fuel reserves and the severe environmental crisis. [1][2][3][4][5][6] Many photocatalytic systems, including semiconductors, [7,8] metal complexes, [9] biomolecules, [10] and organic donorbridge-acceptor systems, [11][12][13][14][15][16][17] have been proposed for such applications. Among these systems, the organic donorbridge-acceptor system is particularly promising due to the flexibility of the molecular design to control the energytransfer behaviour and the absorption of light.…”

Convergent Synthesis of Near‐Infrared Absorbing, “Push–Pull”, Bisthiophene‐Substituted, Zinc(II) Phthalocyanines and their Application in Dye‐Sensitized Solar Cells

“…[3] Due to strong absorption in the red and near-infrared (NIR) regions of the solar spectrum (between 640-700 nm), suitable photophysical properties, and remarkable chemical and thermal stability, phthalocyanines (Pcs) are perhaps the most extensively studied molecules, among the organic dyes, in the areas of molecular electronics and solar-energy conversion. [4] Serious efforts have been made to exploit the application of Pcs in DSSCs. [5] However, until very recently the photovoltaic performance of Pc-sensitized solar cells has been poor (below h = 1 %), owing to strong aggregation and lack of directionality in the excited state.…”

“…Effect of a scattering layer on Pc-sensitized solar cells. [a] NH4 Cl solution (50 mL). The mixture was extracted with ethyl acetate (2 50 mL) and the combined organic extracts were washed with brine (10 mL), dried over MgSO 4 and evaporated in vacuo.…”

High Dilutions of a Drug of Covid-19 Origin Show Difference in Ranks

“…The authors used methanol, but the phenomenon is likely to occur in EtOH. Many CT reactions occur in organized assemblies of molecules [31].…”