Electron transfer in oriented donor-acceptor dyads, intralayer charge migration, and formation of interlayer charge separated states in multi-layered Langmuir-Schäfer films

Photoinduced intra- and interlayer electron transfer (ET) of doubly bridged donor-acceptor molecule, porphyrin-fullerene dyad (PF), was studied in single- and multi-layered Langmuir-Schäfer (LS) films and in LS films, where PF and an efficient electron donating polymer polyhexyltiophene (PHT) formed a bilayer PHT/PF and multi-layered PHT/PF structures. The ET through layers were investigated by a method, which measures the photovoltaic (PV) response proportional to the number of charge-separated (CS) states and to the CS distance between the electrons and holes formed in pulsed photo-excitation. Primary conclusions were, that ET starts as formations of CS dyads (P⁺F^-) in single-layers, continues as long-range intra-layer charge migrations following interlayer CS between two adjacent monolayers. Quantitative conclusions were, that the interlayer ET efficiency is 100% in the bi-layered PF structure (2PF), where two CS dyads in adjacent layers forms CS complexes (P⁺F/PF^-) and that the probability to form longer or higher order of CS complexes follows an expression of a convergent geometric series, with a converting factor of 2/3. In the PHT/PF bilayer structure the ET efficiency was one order of magnitude higher, than that for the 2PF structure due to the ET from the CS dyads to ground state electron donor PHT, with an acceptor density, much higher than that of (P⁺F^-).

Design, synthesis and photophysical studies of phenylethynyl-bridged phthalocyanine-fullerene dyads

A zinc and a free base phthalocyanine-fulleropyrrolidine dyad in which the chromophores are linked by a phenylethynyl group have been prepared using a new synthetic route, and their photoelectrochemical properties have been investigated. The zinc dyad is readily soluble in a variety of solvents, and its spectroscopic properties have been determined in toluene and benzonitrile. In toluene, excitation of the zinc phthalocyanine is followed by rapid establishment of an equilibrium between the phthalocyanine and fullerene excited states. These excited states decay mainly to the ground state and the respective triplet states. The fullerene triplet then transfers its energy to form the phthalocyanine triplet. About 20% of the phthalocyanine excited states lead to formation of a charge-separated state. In benzonitrile, the same decay pathways are observed, but photoinduced electron transfer is much faster, and generates the charge separated state with a quantum yield of ≥85%. The charge separated state has a lifetime of 2.8 ns in toluene and 94 ps in benzonitrile.

Monoisomeric phthalocyanine-fullerene dyads with e- and cis-3 addition pattern; synthesis, modeling, photovoltage and solar cell experiments

Synthesis and characterization of two A 2 B 2-type monoisomeric phthalocyanines and phthalocyanine-fullerene (Pc- C 60) dyads, in which fullerene is regioselectively attached to phthalocyanine with two linkers, are described. 1 H NMR spectroscopy results clearly indicate an e addition pattern of the fullerene moiety in trans-dyad 9, and apparently a cis-3 addition pattern in cis-dyad 10. The possible spatial arrangements of 9 and 10 were further examined by molecular modeling. The dyads have polar (– OH ) side chains on the fullerene side of the dyad providing a possibility to produce oriented donor–acceptor (D–A) Langmuir monolayers on aqueous subphase, which can be shifted onto a solid surface. When deposited on a solid electrode material, parallel vertical alignment of the phthalocyanine and fullerene moieties in 100% dyad monolayer was obtained and vertical electron transfer from Pc to C 60 upon photoexcitation was demonstrated. Introduction of the dyads as an oriented interfacial monolayer between the photoactive layer and metal anode improved the power conversion efficiency in inverted organic solar cells.

Atropisomerism and conformational aspects of meso-tetraarylporphyrins and related compounds

This review provides a comprehensive description of the atropisomerism of meso-di- and tetraarylporphyrins with substituents in ortho-positions of the aryl ring, as well as in corroles and in conveniently substituted phthalocyanines. Different methods of study were examined: X-ray crystallography, NMR spectroscopy (both static and dynamic aspects), classical kinetics, HPLC and theoretical calculations. Then the four atropisomers, the tautomerism of the inner protons, the 'picket fence' concept, conformationally restricted meso-tetraarylporphyrins and the influence of the metal on the conformation were discussed based on 250 references.

Covalent phthalocyanine-fullerene dyads: synthesis, electron transfer in solutions and molecular films

Phthalocyanine-fullerene dyads have being under intensive development and investigation during past decade. Strong absorption of the phthalocyanine chromophore in the red part of the spectrum and ability of the dyad to perform efficient photoinduced charge transfer in non-polar media make them particularly attractive for organic optoelectronic applications. This microreview will focus on covalently linked phthalocyanine-fullerene conjugates in solutions and solid nanostructures. The covalent bonding enables sufficient degree of control over mutual organization of the donor and acceptor parts, and makes possible to investigate the relationships between molecular structure and functioning of single molecules and molecular assemblies.