Efficient Photoinduced Charge Transfer Research Articles

CdIn2S4/g-C3N4 heterojunction photocatalysts: enhanced photocatalytic performance and charge transfer mechanism

CdIn2S4/g-C3N4 heterojunction with excellent photocatalytic activities have been synthesized. The enhanced photocatalytic performance might be ascribed to the efficient photoinduced charge transfer derived from the heterojunction structure.

Efficient photoinduced charge transfer in chemically-linked organic-metal Ag-P3HT nanocomposites

A novel nanocomposite of P3HT and Ag nanoparticles (Ag-P3HT) has been synthesized by laser ablation. The fluorescence wavelength of the nanocomposite can be tuned by varying the ablation duration. The steady-state emission maximum at 580 nm for pristine P3HT shows significant blueshift to wavelengths ranging from 520 to 550 nm for Ag-P3HT. NMR, FTIR and XPS spectroscopy confirm that chemical links are formed between P3HT and silver nanoparticles (NPs) in the nanocomposite. For the sample with an emission maximum at 530 nm, 1H NMR spectra indicate that 66% of the P3HT thiophene ring protons are replaced by Ag NPs. Time-resolved spectroscopy demonstrates that charge transfer efficiency increases for Ag-P3HT and this is attributed to the enhanced intimate interfacial contact between the chemically-bonded metal NPs and polymer chains. The synthetic route outlined provides a one-pot and green strategy for producing metal-organic polymeric materials, with controlled luminescence wavelengths and efficient photoinduced charge transfer that meet the requirement for developing high-performance organic light-emitting and photovoltaic devices.

Enhanced Solar Hydrogen Generation by a Heterojunction of Perovskite-type La2 Ti2 O7 Nanosheets Doped with CdS Quantum Dots.

A heterojunction of a perovskite-type La2 Ti2 O7 (LTO)/CdS quantum dot (QD) nanocomposite was prepared by the chemical bath deposition method. The solar-light-driven H2 generation results show that this CdS QDs/LTO heterojunction exhibits great improvement in the photocatalytic H2 production and its photoelectrochemical properties in comparison with pure CdS QDs and LTO nanosheets. A possible enhanced mechanism of photoinduced interfacial charge transfer between CdS and LTO is proposed for the heterojunction. The shift of the CdS conduction band (CB) edge can enlarge the CB potential difference between CdS QDs and LTO, enhancing transferred driven force of the interfacial electrons and finally improving the two components' separation activity of photogenerated carriers. This study provides a promising method for constructing an efficient photoinduced interfacial charge transfer over LTO and CdS QD heterojunctions for photocatalytic hydrogen production.

Visible-Light-Driven Photoelectrochemical and Photocatalytic Performance of NaNbO3 /Ag2 S Core-Shell Heterostructures.

Herein, we report the fabrication of visible-light-active NaNbO3 /Ag2 S staggered-gap core-shell semiconductor heterostructures with excellent photoelectrochemical activity toward water splitting, and the degradation of a model pollutant (methylene blue) was also monitored. The heterostructures show a pronounced photocurrent density of approximately 2.44 mA cm(-2) at 0.9 V versus Ag/AgCl in 0.5 m Na2 SO4 and exhibit a positive shift in onset potential by approximately 1.1 V. The high photoactivity is attributed to the efficient photoinduced interfacial charge transfer (IFCT). The core-shell design alleviates the challenges associated with the electron-hole paths across semiconductor junctions and at the electrolyte-semiconductor interface. These properties demonstrate that NaNbO3 /Ag2 S core-shell heterostructures show promising visible-light photoactivity and are also efficient, stable, and recyclable photocatalysts.

Investigation of Donor/acceptor Composition Ratio and Annealing Effects on Performances of Organic Solar Cells based on P3HT:C<sub>60</sub>

The optimization of organic photovoltaic (OPV) devices based on a thin-film blend of the polymer poly(3-hexyl thiophene) [P3HT] and the fullerene [C60] was explored. To achieve an efficient photo induced charge transfer, the following aspects have been studied: (1) Determination of the donor/acceptor composition ratio that yields good film interface and high photon absorption; (2) Selection of suitable Nanoparticle to obtain optimal absorption spectrum and good efficiency; (3) Thermal annealing process to enhance the photon absorption, improve the short circuit current and the filling factor, and therefore the efficiency of the devices. In particular, the preparation of the composition and thermal treatment of the active layer along with the effect of Nanoparticle's presence are addressed. In addition, the use of Nanoparticle (WO3) into the P3HT/C60 layer to improve the power conversion efficiency (PCE) of the device is investigated. WO3 Nanoparticle's doped poly(3-hexylthiophene) and C60 blends (P3HT:C60: WO3) have been produced as the photoactive layer of organic photovoltaic devices (OPVs). The 40 ppm WO3 doping OPVs exhibit higher power conversion efficiency (PCE) than other OPVs.

Quantum dot decorated aligned carbon nanotube bundles for a performance enhanced photoswitch.

Photoactive materials that are triggered by the irradiation of light to generate an electrical response provide an ecofriendly platform to afford efficient power sources and switches. A chemical assembly of well-known elements with aligned carbon nanotube bundles is reported here, which was employed to form an efficient photo-induced charge transfer device. The primary elements of this device are ultra-long multi-walled carbon nanotube (MWCNT) bundles, polyaniline (PANI) thin film coating, and CdSe quantum dots (QDs). Highly ordered and horizontally aligned MWCNT bundles were coated with PANI to enhance charge transfer properties of active QDs in this platform. The obtained device (CdSe-MWCNT@PANI) constructed on a silicon base exhibits highly efficient power conversion capabilities owing to the aligned MWCNT bundle assisted enhanced charge transport pathways generated within the device. The device also shows a short circuit current density (Jsc) of 9.81 mA cm(-2) and an open circuit voltage (Voc) of 0.46 V. The power conversion efficiency (PCE) of the device is 5.41%, and the current response is quite stable, highly responsive, and reproducible.

Efficient Excited-State Symmetry Breaking in a Cationic Quadrupolar System Bearing Diphenylamino Donors.

We report a joint experimental and theoretical investigation of a quadrupolar D-π-A(+) -π-D system, the electron donors being diphenylamino groups and the electron acceptor being a methylpyridinium, in comparison with the dipolar D-π-A(+) system. The emission spectra of the two compounds overlap in all the investigated solvents. This finding could be rationalized by TD-DFT calculations: the LUMO-HOMO molecular orbitals involved in the emission transition are localized on the same branch of the quadrupolar structure that becomes the fluorescent portion, corresponding to that of the single-arm compound. Excited-state symmetry breaking has been rarely observed for quadrupolar systems showing negative solvatochromism and is here surprisingly revealed, even in low polarity solvents. Femtosecond transient absorption measurements revealed that an efficient photoinduced intramolecular charge transfer takes place in the quadrupolar chromophore, more efficient than in its dipolar analogue. This result is promising in view of the application of these compounds as novel two-photon absorbing materials.

Conjugated Polyelectrolyte-Induced Self-Assembly of Alkynylplatinum(II) 2,6-Bis(benzimidazol-2'-yl)pyridine Complexes.

Water-soluble cationic alkynylplatinum(II) 2,6-bis(benzimidazol-2'-yl)pyridine (bzimpy) complexes have been demonstrated to undergo supramolecular assembly with anionic polyelectrolytes in aqueous buffer solution. Metal-metal-to-ligand charge transfer (MMLCT) absorptions and triplet MMLCT ((3) MMLCT) emissions have been found in UV/Vis absorption and emission spectra of the electrostatic assembly of the complexes with non-conjugated polyelectrolytes, driven by Pt⋅⋅⋅Pt and π-π interactions among the complex molecules. Interestingly, the two-component ensemble formed by [Pt(bzimpy-Et){CCC6 H4 (CH2 NMe3 -4)}]Cl2 (1) with para-linked conjugated polyelectrolyte (CPE), PPE-SO3 (-) , shows significantly different photophysical properties from that of the ensemble formed by 1 with meta-linked CPE, mPPE-Ala. The helical conformation of mPPE-Ala allows the formation of strong mPPE-Ala-1 aggregates with Pt⋅⋅⋅Pt, electrostatic, and π-π interactions, as revealed by the large Stern-Volmer constant at low concentrations of 1. Together with the reasonably large Förster radius, large HOMO-LUMO gap and high triplet state energy of mPPE-Ala to minimize both photo-induced charge transfer (PCT) and Dexter triplet energy back-transfer (TEBT) quenching of the emission of 1, efficient Förster resonance energy transfer (FRET) from mPPE-Ala to aggregated 1 molecules and strong (3) MMLCT emission have been found, while the less strong PPE-SO3 (-) -1 aggregates and probably more efficient PCT and Dexter TEBT quenching would account for the lack of (3) MMLCT emission in the PPE-SO3 (-) -1 ensemble.

Synthesis and structure of BiPbO2Cl nanosheet with enhanced visible light photocatalytic activity

Through the incorporation of Pb2+ into the [Bi2O2] layers, the BiPbO2Cl nanosheets with layered structure have been successfully synthesized by one-step solvothermal method. The lattice parameters of tetragonal BiPbO2Cl are a=3.9417(2)Å and c=12.3957(6)Å, where the c value is considerably smaller than previous results. The structure of BiPbO2Cl was then readdressed through Rietveld refinement and aberration-corrected scanning transmission electron microscope investigations. The photo-decomposition experiments demonstrated that BiPbO2Cl nanosheet exhibits high photocatalytic activity, which is 12.6 times higher than that of BiPbO2Cl bulk. The photocurrent measurement suggests a more efficient photoinduced charge separation and transfer in BiPbO2Cl nanosheet.

Efficient Nanostructured Biophotovoltaic Cell Based on Bacteriorhodopsin as Biophotosensitizer

Here, we report on utilizing a photoactive protein, bacteriorhodopsin (bR), as a light harvester in combination with TiO2 nanoparticles in biosensitized solar cell application. Experiments have been conducted to investigate the capability of surface adsorption of bR on nanoparticular TiO2photoanodes. Different pretreatment processes have been done to modify the interface of TiO2 nanoparticles and bR as a biophotosensitizer. Our results indicate the feasibility of efficient immobilization and photoinduced charge transfer of bR to the nanostructured TiO2 photoelectrode. Under illumination of simulated AM1.5 sunlight, the solar-light-to-electricity conversion efficiency of the designed solar cell, composed of nanoparticular and nanofibrous layers, reached up to 0.35%, with an open circuit voltage of 533 mV and photocurrent density of 1 mA cm–2. This optimized design of our bR-sensitized solar cell shows superior energy conversion efficiency in comparison to previously reported studies.

Ag–BiOCl nanocomposites prepared by the oxygen vacancy induced photodeposition method with improved visible light photocatalytic activity

Ag–BiOCl nanocomposites were prepared through a visible light induced photodeposition method by taking the advantage of oxygen vacancy in {001} facets of BiOCl. The prepared Ag–BiOCl (Vis–Ag–BiOCl) could efficiently degrade methyl orange (MO) and oxidize NO under visible light irradiation. Moreover, it exhibited an enhanced visible light driven photocatalytic activity compared to Ag–BiOCl (UV–Ag–BiOCl) nanocomposites prepared by the traditional UV light photodeposition method, even that the latter showed a much stronger visible light absorption ability. Photocurrent and electrochemical impedance spectroscopy (EIS) tests indicated that the more efficient photoinduced charge separation and transfer in Vis–Ag–BiOCl could be attributed to the improvement of the visible light photocatalytic activity.

Facile interfacial charge transfer across hole doped cobalt-based MOFs/TiO2 nano-hybrids making MOFs light harvesting active layers in solar cells

Hole doping leads to an efficient photo-induced interfacial charge transfer from MOFs to TiO2 and thereby the MOFs can harvest solar radiation to generate electricity.

DNA-assisted photoinduced charge transfer between a cationic poly(phenylene vinylene) and a cationic fullerene

Water-soluble cationic conjugated poly(phenylene vinylene) (PPV) and cationic fullerene were complexed with negatively charged single stranded DNA and double stranded DNA via electrostatic interactions to achieve photoinduced charge transfer with efficiencies as high as those observed from oppositely charged, cationic PPV and anionic fullerene but with distinctly different quenching mechanisms.

Poly(3-hexylthiophene)/hexamine modified ZnO hybrid nanocomposite: structural, optical, thermal and electrical transport studies

This paper reports the synthesis of poly(3-hexylthiophene) (P3HT)/HA@ZnO nanocomposite by in situ polymerization and demonstrates their thermal, morphological and optoelectronic properties. Zinc oxide (ZnO) nanoparticles were prepared by the simple approach of co- precipitation method using zinc acetate dihydrate as precursor modified by hexamine (HA) acting as a capping agent. Structural and photo physical studies shows that conjugated polymer chains intimately contact with the inorganic semiconductor. ZnO has wurtzite structure with average crystallite size of 40 nm. The emission spectra indicate that modified ZnO nanoparticles results in more efficient photo induced charge transfer than that of the simple nanocomposite of P3HT/ZnO. The morphological studies revealed that the transformation of granular morphology of P3HT to the clusters in P3HT/HA@ZnO hybrid nanocomposites. Cyclic voltammeter elucidates the electrochemical behavior and the HOMO–LUMO energy levels of the nanocomposites. The results indicate that the P3HT/HA@ZnO nanocomposite has energy gap of 0.72 eV, indicating this composite has potential for the fabricating hybrid organic–inorganic solid state solar cells. A solar to electric energy conversion efficiency of 0.1238 % was attained with the system.

Towards high-efficiency non-fullerene organic solar cells: Matching small molecule/polymer donor/acceptor

Two low band-gap donors, small molecule p-DTS(FBTTh2)2 (SD) and polymer PBDTTT-C-T (PD), and two perylene diimide acceptors, small molecule PDI-2DTT (SA) and polymer PPDIDTT (PA), were used to fabricate non-fullerene organic solar cells. The effects of four donor/acceptor combinations, PD/PA, PD/SA, SD/SA and SD/PA, on the morphology, charge transfer, charge transport and photovoltaic performance were investigated. Power conversion efficiencies (PCEs) of PD/PA, PD/SA, SD/SA and SD/PA were 3.04%, 0.28%, 2.52% and 0.29%, respectively. The PD/PA blend and SD/SA blend exhibited relatively uniform and continuous morphology, efficient photoinduced charge transfer, high mobility and balanced charge transport relative to PD/SA and SD/PA blends, leading to much higher PCEs.

Fluorescent Nanomicelles for Selective Detection of Sudan Dye in Pluronic F127 Aqueous Media

Novel self-assembled water-soluble nanomicelles that contain fluorescent conjugated polymers (poly(9,9-dioctylfluorene) (PFO) or poly[2,7-(9,9-dihexylfluorene)-alt-4,4'-phenylether] (PF-PE)) have been obtained and used as the highly sensitive/selective platform for Sudan dye detection. The Fluorescent nanomicelles exhibited a highly selective fluorescence quenching by the prohibited food additive Sudan I, while not for the natural pigments: Capsanthin and Beta-carotene, due to the more suitable matching of the LUMOs (lowest unoccupied molecular orbital) of the conjugated polymers with that of Sudan I molecules. The Stern-Volmer constants (K(SV)) of PF-PE/F127 and PFO/F127 for Sudan I were 1,040,480 and 665,000 M(-1), respectively, which were more than 100 times higher than those of the same conjugated polymers in the orgainc solvents. The significantly enhanced sensitivity was due to the collective effect of the F127 micelles to both chromophore and analyte, through which the fluorophone-analyte binding interaction is significantly strengthened and efficient photoinduced charge transfer occurs. The as-proposed materials and approach may be potentially applied in the real-time food safety screening.

Effect of Mutual Position of Electron Donor and Acceptor on Photoinduced Electron Transfer in Supramolecular Chlorophyll–Fullerene Dyads

In this study we have explored the influence of mutual position of chlorin electron donor and fullerene C60 electron acceptor on photoinduced electron transfer. Two zinc-chlorin-aza-[18]crown-6 compounds and three pyrrolidino[60]fullerenes with alkyl aminium and varying coordinative moieties were synthesized and used for self-assembling of a set of complexes via two-point binding. The aza[18]crown6 moieties were connected to chlorins via amide linker either at 13(4) or 17(4) position, hence, being attached on different sides of the chlorin plane. Furthermore, in the former case, the linker holds the crown closely spaced, whereas, in the latter, the linker gives more space and conformational freedom for the crown with respect to the chlorin macrocycle. The coordinative moieties at fullerene site, 3-pyridine, 4-pyridine, and 3-furan, were built by utilizing the Prato reaction. The two-point binding drove the molecules into specific complex formation by self-assembling; aminium ion was chelated by crown ether, while zinc moiety of chlorin was coordinated by pyridine and furan. Such pairing resulted in distinct supramolecular chlorin-fullerene dyads with defined distance and orientation. The performed computational studies at DFT level in solution, with TPSS-D3/def2-TZVP//def2-SVP, indicated different geometries and binding energies for the self-assembling complexes. Notably, the computations pointed out that for all the studied complexes, the donor-acceptor distances and binding energies were dictated by chirality of pyrrolidino ring at C60. The selective excitation of chlorin chromophore revealed efficient emission quenching in all dyads. The ultrafast spectroscopy studies suggested a fast and efficient photoinduced charge transfer in the dyads. The lifetimes of the charge separated states range from 55 to 187 ps in o-dichlorobenzene and from 14 to 60 ps in benzonitrile. Expectedly, the electron transfer rate was found to be critically dependent on the donor-acceptor distance; additionally, the mutual orientation of these entities was found to have significant contribution on the rate.

The surface-enhanced Raman scattering from ZnO nanorod arrays and its application for chemosensors

Based on the surface-enhanced Raman scattering (SERS) of two similar probe molecules, 4-mercaptopyridine (4-MPY) and 4-aminothiophenol (PATP) from the ZnO nanorod arrays (ZnONRs) substrates, the prerequisite of SERS for ZnONRs-molecules system was investigated. The results indicated that the realization of efficient photo-induced charge transfer between ZnONRs and the probed molecules is a critical prerequisite to magnify polarizability tensor of the probed molecular and realize SERS. Such results were also verified by the SERS performance of the dye (Bu4N)2[Ru(dcbpyH)2-(NCS)2] (N719) and acetaminophen as the probe molecules on the ZnONRs substrates. The linear relation between the logarithmic concentrations and Raman peak intensities afforded quantitative detection of N719 and acetaminophen. Significantly, the evident SERS response of N719 and acetaminophen from the ZnONRs substrates not only provided a significant insight into the behaviors of the photo-induced charges for dye-sensitized solar cells (DSSCs), but also demonstrated that the present SERS-active substrate could be utilized as a chemosensor for pharmaceutical analysis.

Donor–Acceptor Random Copolyesters containing Perylenebisimide (PBI) and Oligo(p-phenylene vinylene) (OPV) by Melt Condensation Polymerization: Energy Transfer Studies

Novel copolyesters consisting of oligo(p-phenylene vinylene) (OPV) as donor (D) and perylenebisimide (PBI) as acceptor (A) were synthesized by melt polycondensation. Photoinduced energy transfer and photoinduced charge separation in these polyesters were studied in solution as well as in the solid state. Selective excitation of OPV moiety resulted in the energy transfer with >90% efficiency from OPV to PBI chromophore in the solution state. The direct excitation of PBI in the D-A copolyester resulted in reduced fluorescence emission of acceptor, indicating electron transfer between the D and A moieties. The effect of distance between donor and acceptor on the energy transfer efficiency from donor to acceptor was studied. Compared to a physical mixture of D and A polyesters alone, the energy transfer was 4 times more efficient in the D-A copolyester, highlighting the influence of covalently linking D and A in a single polymer chain. A strong fluorescence quenching (∼ 100%) of both chromophores in solid state indicated an efficient photoinduced charge transfer after photoexcitation of either D or A. Thus, OPV-PBI main chain copolyester is an excellent system for the study of energy- and electron-transfer processes in organic semiconductor. Reactive blend of D/A copolyester was also prepared by the transesterification reaction between D and A alone copolyesters. The energy transfer efficiency from D to A moiety upon selective excitation of D chromophore in the D/A copolyester blend was ∼4 times higher compared to a physical mixture of D and A alone copolyesters, which gave direct proof for the transesterification reaction in polyester/polyester reactive blending.

Fluorine–thiophene-substituted organic dyes for dye sensitized solar cells

Novel triphenylamine (TPA)-based organic dyes were synthesized and assessed for their performance in dye-sensitized solar cells (DSSCs). In the dyes considered the TPA group and the cyanoacetic acid have the role of electron-donor and -acceptor, respectively, whereas a thienyl–fluoro-phenyl-substituted was introduced as π-linker to improve the dye performance in DSSCs. Experimental characterizations empasize that the presence of electron withdrawing substituents in the linker close to the electron-acceptor moiety leads to a more efficient intramolecular photoinduced charge transfer. In fact, photovoltaic experiments reveal that the DSSCs based on the thienyl–o-fluoro-phenyl substituted dyes yield a better solar-energy-to-electricity conversion efficiency.