Vectorial Photoinduced Electron Transfer Research Articles

Microsecond charge recombination in a linear triarylamine–Ru(bpy)32+–anthraquinone triad

Linear triads with ruthenium photosensitizers are frequently based on the Ru(terpyridine)(2)(2+) unit. We report on vectorial photoinduced electron transfer in a linear triad based on the Ru(bipyridine)(3)(2+) photosensitizer. Electron-hole separation over a 22 Å-distance is established with a quantum yield greater than 64% and persists for 1.3 μs in acetonitrile.

Vectorial photoinduced electron transfer in multicomponent film systems of poly(3-hexylthiophene), porphyrin—fullerene dyad, and perylenetetracarboxidiimide

Multistage electron transfer in a film system consisting of a hole-transporting layer (HTL), donor-acceptor pair (D-A), and an electron-transporting layer (ETL) was studied by photovoltage and flash-photolysis techniques. Poly(3-hexylthiophene) (PHT) was used as the HTL, while a symmetric porphyrin-fullerene dyad (P-F) and perylenetetracarboxidiimide (PTCDI) layers were functioning as the D-A pair and ETL, respectively. The photoexcitation of this three-component film system causes charge separations in the monomolecular P-F film, followed by electron transfer from the PHT polymer film and the fullerene anions to the porphyrin cations and the PTCDI layer, respectively. The final transient state is a charged PHT(+)|P-F|PTCDI(-) system, with significantly increased amplitude and lifetime of the photoelectrical signals compared to previously studied P-F|PTCDI and PHT|P-F systems, due to the its increased charge-separation distance. The study promotes the knowledge on the charge transfer mechanism in multilayered film systems.

Supramolecular Donor−Acceptor Hybrid of Electropolymerized Zinc Porphyrin with Axially Coordinated Fullerene: Formation, Characterization, and Photoelectrochemical Properties

Photoelectrochemical behavior of self-assembled C60 via axial coordination to an electrochemically polymerized zinc porphyrin film was systematically investigated to unravel the importance of the coordinated fullerene in improving the photocurrent and photovoltage generation of the resulting donor−acceptor dyad. For this, tetrakis(4-(N,N-diphenylamino)-phenyl)porphyrinato-zinc(II), (Ph2N)4ZnP, bearing electropolymerizable triphenylamine peripheral substituents was first electropolymerized to form a film on the electrode surface. The resulting formation of the electrochemically active and dense film was confirmed by using an electrochemical quartz crystal microbalance (EQCM) and by atomic force microscopy imaging. The optical absorption and emission studies revealed the characteristic absorption and emission bands of zinc porphyrin that suggested preservation of the π-electron system of the porphyrin monomer in the polymer. Further, the fullerene, derivatized with an axially coordinating imidazole ligand, was allowed to self-assemble via axial coordination to the zinc center of the (Ph2N)4ZnP polymer film. The simultaneously performed piezoelectric microgravimetry and cyclic voltammetry studies using EQCM allowed us to prove this coordination and to evaluate the redox potential of the donor, (Ph2N)4ZnP, and acceptor, C60, moiety. The fluorescence emission results, along with the free energy calculations, suggested the occurrence of vectorial photoinduced electron transfer from the singlet-excited ZnP in the polymer to the axially coordinated fullerene moiety. Systematic photoelectrochemical studies revealed cathodic photocurrent generation, a result unlike most of the dye-sensitized photoelectrochemical cells reported in the literature. Moreover, the coordinated fullerene to the zinc porphyrin film improved the photocurrent and photovoltage generation of the photoelectrochemical cell. An incident photon-to-current conversion efficiency (IPCE) of nearly 2% at the Soret region of maximum absorption was determined for the [(Ph2N)4ZnP polymer]−fullerene hybrid film.

Interlayer photoinduced electron transfer in Langmuir-Blodgett films based on porphyrin and phthalocyanine derivatives

Vectorial photoinduced electron transfer was studied in Langmuir-Blodgett films. The monolayers of polythiophene and phthalocyanine were used as secondary electron donors in multilayers together with the monolayer of porphyrin-fullerene donor-acceptor dyad molecules mixed with octadecylamine (1:9). Simultaneous utilization of all the three compounds in the preparation of three-layer samples allowed us to widen the range of the visible light absorption by the structure. The relative sensitivity of the sample to the excitation laser light increased by about 350 times compared with that of a dyad monolayer.

Impedance modulation of polymer nanosheet capacitor by light stimuli

We report the modulation of dielectric properties of photoactive ultrathin polymer film capacitor (polymer nanosheet capacitor) constructed from polymer nanosheet assemblies. The capacitor was fabricated from multi-heterodeposition of passive polymer nanosheet, poly(N-dodecylacrylamide) (p(DDA)) and two photoactive nanosheets, which contain ruthenium and ferrocene, respectively. The impedance spectroscopy measurement indicates that the photoactive capacitor acts as an ideal capacitor in a dark condition. To modulate dielectric properties of the photoactive capacitor, the capacitor was irradiated with a visible light to excite the ruthenium complex. After 5min irradiation, the impedance spectrum of the photoactive capacitor shows deviation from an ideal capacitor behavior. The deviation was derived from a vectorial photoinduced electron transfer between ruthenium and ferrocene. An equivalent-circuit for the irradiated nano-capacitor was proposed and the capacitance derived from the photoinduced electron transfer was determined to 8.6nF/cm2.

Synthesis and photoelectrochemical properties of ruthenium bisterpyridine sensitizers functionalized with a thienyl phosphonic acid moiety

We report herein the preparation, the electrochemical, the absorption and the emission properties of new heteroleptic bisterpyridine ruthenium complexes composed of a terpyridine functionalized on the 4′ position by a thienyl phosphonic acid. The complexes were tested in TiO 2 dye-sensitized solar cells and were investigated by ultrafast transient IR spectroscopy on TiO 2 and SnO 2 electrodes. We found that the complex, in which the phosphonic acid group is separated by a thienyl unit to the terpyridine, displays a faster electron injection rate into the semiconductor conduction band and an improved photovoltaic photoconversion efficiency compared to the analogous complex in which the phosphonic acid group is directly linked to the terpyridine. This indicates that the thienyl unit does not restrict electron injection from the MLCT excited-state. This study highlights the benefit of introducing a thienyl unit between the phosphonic acid anchoring group and the polypyridine ruthenium sensitizer for the designing of sensitizers for solar cells and for the development of multi-molecular arrays for vectorial photoinduced electron transfer with semiconductor surface.

Photoinduced interlayer electron transfer in alternating porphyrin–fullerene dyad and regioregular poly(3-hexylthiophene) Langmuir–Blodgett films

Alternating Langmuir–Blodgett (LB) bi-layer structures containing a donor–acceptor (DA) dyad layer and a layer of conducting polymer were used to study interlayer vectorial photoinduced electron transfer (VPET). The used porphyrin–fullerene dyads were known to be capable of VPET, from the porphyrin to fullerene moiety, as a LB monolayer structure. The DA dyad and the poly(3-hexylthiophene), PHT, layers were deposited as adjacent LB monolayers in order to promote the secondary electron transfer from the polymer to the porphyrin cation, the product of the primary electron transfer. The VPET reaction was studied with the time-resolved Maxwell displacement charge (TRMDC) method both in the photovoltage (PV) and photocurrent (PC) modes. The PHT monolayer at the side of the porphyrin moieties lengthened the charge separation (CS) distance. Because of PHT the photovoltage amplitudes were increased and the recombination kinetics of the charge-separated state was delayed. The electron transfer direction in the bi-layer system was determined by the orientation of the DA dyad. The charge separation in the system took place with yield close to unity.

Vectorial photoinduced electron transfer of phytochlorin-fullerene systems in Langmuir-Blodgett films

Molecular systems capable of photoinduced vectorial electron transfer (ET) were assembled using the Langmuir-Blodgett technique. The active part of the systems consisted of phytochlorin-fullerene donor-acceptor layers and polythiophene secondary donor layers. Such structures can promote multi-step inter-layer ET in a direction determined by the film architecture. Transient photovoltage and photocurrent were studied and ET rates and efficiencies were determined. The primary intramolecular charge separated state was formed upon photoexcitation in less than 1 ns and it recombined in approximately 50 ns. Addition of the polythiophene layer at the side of the phytochlorin moieties increased the distance of charge transfer and the lifetime of the charge separated state by promoting spontaneous interlayer electron transfer from the polymer to the phytochlorin cation.

Vectorial photoinduced electron transfer in alternating Langmuir–Blodgett films of phytochlorin–[60]fullerene dyad and regioregular poly(3-hexylthiophene)

Alternating Langmuir–Blodgett (LB) bilayer structures, consisting of a donor–acceptor (DA) layer of a phytochlorin–fullerene (PF) dyad and a layer of a regioregular poly(3-hexylthiophene) (PHT) polymer were used to study interlayer vectorial photoinduced electron transfer (VPET). As the dyad PF undergoes, under light illumination, an intramolecular ET from the phytochlorin to the fullerene moiety an intralayer VPET takes place in the LB monolayer. When PF was deposited on the PHT layer and excited the second ET took place from the PHT layer to the phytochlorin cation. Thus the PHT layer can act as a secondary electron donor and accompany the primary photoinduced electron transfer in the PF layer by a spontaneous interlayer electron transfer. Important characteristic properties of the VPET bilayer are the longer distance of charge separation (CS) and the longer lifetime of the charge separated state (lifetime from microsecond to second) as compared to VPET of the PF monolayer alone (where the lifetime of CS state was ≈30 ns). The CT measurements were carried out for different molecular orientations and film structures. Models for the multistep photochemical reactions are discussed.

Vectorial Photoinduced Electron Transfer in Phytochlorin−[60]Fullerene Langmuir−Blodgett Films

A novel molecular electron donor−acceptor (DA) dyad, composed of a phytochlorin donor and a [60]fullerene acceptor, was used for the preparation of solid molecular films capable of performing vectorial photoinduced electron transfer (VPET). Being mixed with octadecylamine at concentrations of 50 mol % and lower, the DA compounds form a stable monolayer, which can be transferred onto a solid substrate. Thus prepared Langmuir−Blodgett (LB) monolayer films are characterized by uniform orientation of the DA molecules and, consequently, can undergo VPET. This was confirmed by time-resolved Maxwell displacement charge (TRMDC) measurements. The rate constant for the electron transfer was ca. 109 s-1 as estimated from the fluorescence lifetime measurements. The majority of the charge transfer states of the DA molecules (>60%) recombined with a time constant of ca. 30 ns, being almost independent of the DA concentration in the concentration range from 2 to 50 mol %, as revealed from TRMDC experiments. Therefore, V...

Photoinduced vectorial charge transfer in mixed Langmuir–Blodgett films of 5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)porphyrin and its zinc(ii) derivative

Langmuir–Blodgett films containing 1 mol% 5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)porphyrin (TBP) and its zinc(II) complex (ZnTBP) in a suitable matrix were prepared in an attempt to build a molecular-scale device capable of vectorial photoinduced electron transfer. The films were studied by absorption and fluorescence spectroscopies, and by the time-resolved measurement of Maxwell displacement charge (TRMDC) across the film. The latter experiments showed that photoinduced electron transfer takes place in the films and that its macroscopic direction can be controlled by the molecular orientation. The TRMDC signals were unusually long-lived.

Vectorial PET in LB bilayers and in vesicles: nanosecond fluorescence and laser flash-photolysis investigation

Vectorial photoinduced electron transfer was investigated in Langmuir-Blodgett bilayers and in vesicles with the same phospholipid composition. The donor was covalently bound to one of the Hydrophobie chains of the phospholipid in the mimetic membrane, whereas the acceptor was adsorbed at the polar head group surface. The location of the redox couple was preliminarily determined studying the photophysical properties of the donor in the phospholipid bilayer as well as the process of adsorption of the acceptor at the phospholipid-water interface. The photoinduced electron transfer reaction was studied measuring the quenching of pyrene fluorescence in the presence of increasing concentrations of acceptor, the process was studied both with steady-state and time-resolved fluorescence emission in the nanosecond time scale. The reaction transient species formed upon photoexcitation were identified performing nanosecond laser-flash photolysis experiments in vesicle systems. The dynamics of the charge recombination process following photoinduced electron transfer, was investigated studying the kinetic of decay of the absorption signal of the transient species.

Vectorial photoinduced electron transfer in phospholipid vesicles and LB bilayers

Photoinduced electron transfer (PET) was studied in phospholipid vesicles and in Langmuir-Blodgett bilayers in the attempt to produce a model for electron transfer processes in biological media. Spatial organization of the reaction centers in lipid membranes needs to be controlled in order to provide high efficiency of light-to-chemical energy conversion. We designed a phospholipid system where the donor is localized in the inner bilayer whereas the acceptor is at the polar groups-water interface. We used dipalmitoylphosphatidic acid vesicles containing low molar fractions of dipalmitoylphosphatidylcholine with pyrene (donor) bound to one of the alkyl chains. Methylviologen (acceptor) was added to the external aqueous phase; upon photoexcitation of the donor we observed the electron transfer to take place in a unidirectional manner from the inside of the bilayer to the interface. Information about the location of the donor was obtained studying the photophysical properties of the pyrene chromophore in vesicles and in LB layers. The photoinduced electron transfer reaction was evidenced by quenching of pyrene fluorescence in the presence of increasing concentrations of acceptor, the process was studied both with steady-state and time-resolved fluorescence emission. Fluorescence intensity was found to decrease with increasing concentration of methylviologen, similar results were obtained for vesicles and LB layers of analog composition immersed in a methylviologen solution. Lifetimes of the excited species were found to be of the same order of magnitude in vesicle and LB-layer systems.

Vectorial photoinduced electron transfer between phospholipid membrane-bound donors and acceptors. [Erratum to document cited in CA117(14):140385p

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTVectorial photoinduced electron transfer between phospholipid membrane-bound donors and acceptors. [Erratum to document cited in CA117(14):140385p]Bruce Armitage and David F. O'BrienCite this: J. Am. Chem. Soc. 1993, 115, 16, 7555Publication Date (Print):August 1, 1993Publication History Published online1 May 2002Published inissue 1 August 1993https://doi.org/10.1021/ja00069a086RIGHTS & PERMISSIONSArticle Views43Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (161 KB) Get e-Alerts Get e-Alerts

Vectorial photoinduced electron transfer between phospholipid membrane-bound donors and acceptors

Photoinduced electron transfer (PET) from the hydrophobic triphenylbenzylborate anion to the water-soluble tricationic N,N'-bis [3-(trimethylammonio)propyl]thiadicarbocyanine was investigated in water and in phosphatidylcholine membrane systems. The borate (donor) and dye (acceptor) form a strong complex in water,leading to inefficient PET. In the presence of liposomes, the hydrophobic borate anion is bound deep within a bilayer. The resulting negative surface charge of the liposomes leads to electrostatic binding of the cationic dye within the head group region of the membrane