Rate Of Photoinduced Electron Transfer Research Articles

Effect of surface ligands on the photoinduced electron transfer rate and efficiency in ZnO quantum dots and graphene oxide assemblies.

Apart from biocompatibility, ZnO quantum dots (QDs) are considered to be an efficient luminescence material due to their low cost and high redox potential. Here, we report the synthesis of ZnO QDs by using five different functionalizing ligands like mercaptoacetic acid (MAA), 3-mercaptopropionic acid (MPA), octadecene (ODE), ethylene glycol (EG), and oleyl amine (OLA) and fabricate their assemblies with graphene oxide (GO). We investigate the role of functionalizing ligands as a surface modifier of ZnO QDs for their attachment to GO. The steady-state photoluminescence (SSPL) and time-resolved photoluminescence (TRPL) analyses demonstrate the photoluminescence (PL) quenching of ZnO QDs in ZnO QDs-GO assembly. The highest reduction in PL intensity is observed with ZnO QDs-GO assembly with EG as a surface functionalizing ligand. Cyclic voltammetry (CV) analysis confirms the feasibility of charge transfer from ZnO QDs to the GO. The maximum (79.43%) charge transfer efficiency (ECT ) is observed in the case of ZnO-MAA-GO as compared to other assemblies. This means the thiol group-containing ligands facilitate charge transfer as compared to hydroxyl and amine group ligands. This leads to the conclusion that charge transfer in ZnO QDs-GO assemblies depends strongly on the nature of surface ligands.

Mechanism of photoinduced electron transfer from tryptophanes to the excited isoalloxazine in animal-like cryptochrome from Chlamydomonas reinhardtii: Molecular dynamics simulation and molecular orbital studies

Cryptochrome from a green alga Chlamydomonas reinhardtii binds flavin adenine dinucleotide (FAD) as a cofactor in a stacked form. The protein structures of the cryptochrome in solution were obtained by means of molecular dynamics simulation (MDS). Mechanisms of photoinduced electron transfer from aromatic chromophores including adenine to the excited isoalloxazine were quantitatively studied with the MDS structures and an electron transfer theory, using the reported experimental rate. The rates were fastest from Trp399, followed by Trp354, Trp332, Trp376, Trp401, Trp294, and adenine. The slower rate from Trp401 despite of the short distance was elucidated with much difference in a net electrostatic energy between the ion-pair and ionic groups in the protein, compared to that in Trp399. The static dielectric constant near isoalloxazine was quite high (7.95), which should be related to a higher number of water molecules near isoalloxazine, compared to those in other non-photoactive flavoproteins. Charge transfer (CT) interactions between isoalloxazine and Trp399 or other Trps (Trp354, Trp332, Trp376, Trp401) were studied by means of a semi-empirical molecular orbital (MO) method. The mean charges transferred from Trps to Iso* over 46 snapshots were −0.514 in Trp399, −0.042 in Trp354, and −0.216 in Trp332, −0.068 in Trp376, and −0.155 in Trp401, which were qualitatively in accordance with the results of photoinduced electron transfer rates. The effect of polarity of the medium on CT interaction was examined with the MO method. The amount of charge transferred from Trp399 to Iso* in the Iso* - Trp399 system decreased with static dielectric constant in the range of 2 to 30.

Aggregation of Charge Acceptors on Nanocrystal Surfaces Alters Rates of Photoinduced Electron Transfer.

Semiconductor nanocrystals (NCs) interfaced with molecular ligands that function as charge and energy acceptors are an emerging platform for the design of light-harvesting, photon-upconverting, and photocatalytic materials. However, NC systems explored for these applications often feature high concentrations of bound acceptor ligands, which can lead to ligand-ligand interactions that may alter each system's ability to undergo charge and energy transfer. Here, we demonstrate that aggregation of acceptor ligands impacts the rate of photoinduced NC-to-ligand charge transfer between lead(II) sulfide (PbS) NCs and perylenediimide (PDI) electron acceptors. As the concentration of PDI acceptors is increased, we find the average electron transfer rate from PbS to PDI ligands decreases by nearly an order of magnitude. The electron transfer rate slowdown with increasing PDI concentration correlates strongly with the appearance of PDI aggregates in steady-state absorption spectra. Electronic structure calculations and molecular dynamics (MD) simulations suggest PDI aggregation slows the rate of electron transfer by reducing orbital overlap between PbS charge donors and PDI charge acceptors. While we find aggregation slows electron transfer in this system, the computational models we employ predict ligand aggregation could also be used to speed electron transfer by producing delocalized states that exhibit improved NC-molecule electronic coupling and energy alignment with NC conduction band states. Our results demonstrate that ligand aggregation can alter rates of photoinduced electron transfer between NCs and organic acceptor ligands and should be considered when designing hybrid NC:molecule systems for charge separation.

Effect of the Donor/Acceptor Size on the Rate of Photo-Induced Electron Transfer

The photo-induced electron transfer has been under intensive investigation for a few decades already, and a good understanding of the reaction was developed based on thorough study of the molecular donor–acceptor (DA) system. The recent shift to hybrid DA systems opens the question of transferring the knowledge to analyze and design these new materials. One of the apparent differences is the size increase of the donor or acceptor entities. The electronic wave functions of larger entities occupy a larger volume, but since these are still one-electron wave functions, their amplitudes are lower. A simple analysis proposed here demonstrates that this leads to roughly inverse third power dependence of the electron transfer rate constant on the donor or acceptor size, kET∝R−3. This dependence can be observed upon switching from molecular to quantum dot donor in DA systems with a fullerene acceptor.

Highly Efficient Luminescence from Charge-Transfer Gold Nanoclusters Enabled by Lewis Acid.

Understanding the complicated intramolecular charge transfer (ICT) behaviors of nanomaterials is crucial to the development of high-quality nanoluminophores for various applications. However, the ICT process in molecule-like metal nanoclusters has been rarely explored. Herein, a proton binding-induced enhanced ICT state is discovered in 6-aza-2-thiothymine-protected gold nanoclusters (ATT-AuNCs). Such an excited-state electron transfer process gives rise to the weakened and red-shifted photoluminescence of these nanoclusters. By the joint use of this newfound ICT mechanism and a restriction of intramolecular motion (RIM) strategy, a red shift in the emission maxima of 30 nm with 27.5-fold higher fluorescence quantum efficiency is achieved after introducing rare-earth scandium ion (Sc3+) into ATT-AuNCs. Furthermore, it is found that upon the addition of Sc3+, the photoinduced electron transfer (PET) rate from ATT-AuNCs to minocycline is largely accelerated by forming a donor-bridge-acceptor structure. This paper offers a simple method to modulate the luminescent properties of metal nanoclusters for the rational design of next-generation sensing platforms.

Efficient Charge Dissociation of Triplet Excitons in Bulk Heterojunction Solar Cells

Understanding the sources of energy loss in bulk heterojunction (BHJ) solar cells is of outstanding importance for increasing power conversion energy. Herein, we employ a full quantum mechanics approach to determine the rates of charge transfer processes at the acceptor–donor interface for a prototypical BHJ blend. It is shown that charge recombination of a singlet charge transfer (CT) state at the acceptor/donor (A/D) interface is very fast, being the most effective process which prevents efficient charge migration toward the electrodes. Triplet CT states can also undergo charge recombination by fast decay to a low lying triplet state of the donor and/or of the acceptor, but the backward process is also fast enough to allow efficient charge dissociation. Slowing down the fast decay process of singlet CT states appears to be hardly practicable, since it would reflect either on a reduced spectral absorption window or on a slow rate of photoinduced electron transfer, so that an alternative and possibly more viable route for increasing organic solar cell efficiency could be that of favoring the formation of triplet CT states over singlet ones.

Resolving electron injection from singlet fission-borne triplets into mesoporous transparent conducting oxides.

Photoinduced electron transfer into mesoporous oxide substrates is well-known to occur efficiently for both singlet and triplet excited states in conventional metal-to-ligand charge transfer (MLCT) dyes. However, in all-organic dyes that have the potential for producing two triplet states from one absorbed photon, called singlet fission dyes, the dynamics of electron injection from singlet vs. triplet excited states has not been elucidated. Using applied bias transient absorption spectroscopy with an anthradithiophene-based chromophore (ADT-COOH) adsorbed to mesoporous indium tin oxide (nanoITO), we modulate the driving force and observe changes in electron injection dynamics. ADT-COOH is known to undergo fast triplet pair formation in solid-state films. We find that the electronic coupling at the interface is roughly one order of magnitude weaker for triplet vs. singlet electron injection, which is potentially related to the highly localized nature of triplets without significant charge-transfer character. Through the use of applied bias on nanoITO:ADT-COOH films, we map the electron injection rate constant dependence on driving force, finding negligible injection from triplets at zero bias due to competing recombination channels. However, at driving forces greater than −0.6 eV, electron injection from the triplet accelerates and clearly produces a trend with increased applied bias that matches predictions from Marcus theory with a metallic acceptor.

Surface modification for improving the photoredox activity of CsPbBr3 nanocrystals.

In recent years inorganic lead halide perovskite nanocrystals (PNCs) have been used in photocatalytic reactions. The surface chemistry of the PNCs can play an important role in the excited state interactions and efficient charge transfer with redox molecules. In this work, we explore the impact of CsPbBr3 nanocrystal surface modification on the excited state interactions with the electron acceptor benzoquinone (BQ) for three different ligand environments: as oleic acid/oleylamine (OA/OAm), oleic acid (OA)/trioctylphosphine (TOP), and oleic acid (OA)/oleylamine (OAm)/trioctylphosphine (TOP) ligands. Our finding concludes that amine-free PNCs (OA/TOP capped) exhibit the best excited state interactions with benzoquinone compared to the conventional oleylamine ligand environment. The photoinduced electron transfer (PET) rate constants were measured from PL-lifetime decay measurement. The amine-free PNCs show the highest PET which is 9 times higher than that of conventional ligand capped PNCs. These results highlight the impact of surface chemistry on the excited-state interactions of CsPbBr3 NCs and in photocatalytic applications. More importantly, this work concludes that amine-free PNCs maintain a redox-active surface with a high photoinduced electron transfer rate which makes them an ideal candidate for photocatalytic applications.

The effect of the rate of photoinduced electron transfer on the photodecarboxylation efficiency in phthalimide photochemistry

Reactivity in photoinduced electron transfer reactions (PET) has been investigated in a series of molecules possessing different distances between the electron donor (carboxylate or alkoxyphenyl) and the phthalimide as the electron acceptor. The molecules were strategically designed to separate the donor and the acceptor by a rigid adamantane spacer or through a peptide backbone with different number of amino acid residues. PET was investigated by laser flash photolysis (LFP). Although previous reports demonstrated that the quantum yields of the photodecarboxylation reaction (ΦR) depend on the distance between the donor and acceptor moieties, the measured lifetimes of the triplet excited state did not provide information on the rates of PET. Due to reversible PET and back electron transfer processes in compounds 1-5, the measured lifetimes correspond to the sum of the rate constants for the disappearance of the charge transfer species. In the series of peptides, three different PET processes take place and LFP provided rate constant for the reactions occurring subsequent to the intrastrand PET between the carboxylate and the alkoxyphenyl radical cation. The understanding of the factors that affect intramolecular PET processes is important for the rational design of different applications.

Effects of protein association on the rates of photoinduced electron transfer from tryptophan residues to excited flavin in medium-chain acyl-Co A dehydrogenase. Molecular dynamics simulation

Rates of photoinduced electron transfer (ET) from tryptophan residues (Trps) to excited isoalloxazine (Iso*) of flavin adenine dinucleotide (FAD) in medium-chain acyl Co A dehydrogenase from porcine kidney (MCAD) have been studied using its entire tetrameric structures obtained by molecular dynamics simulation (MDS) and experimental ultrafast fluorescence decays reported. The ET rates were fastest from Trp166 to Iso* among the four Trps. The emission-wavelength dependent decays were elucidated by introducing emission-wavelength dependent electron affinity of Iso*. The ET rates in Sub C were much slower than those in other subunits, which was ascribed to non-equivalent electrostatic interactions among the subunits. Effect of the protein association on the ET rates and related physical quantities were examined comparing those in the tetramer and monomer reported. The donor-acceptor distances in the tetramer were shorter than those in the monomer. The ET rates from Trp166 in the tetramer were slower than that in the monomer. The ET rates and related physical quantities were examined at seven emission wavelengths. The values of standard free energy gap between the photo-products and reactants displayed to increase as the emission wavelength becomes longer at all subunits. The ET rates displayed to decrease in Sub A, Sub C and Sub D, as the emission wavelength becomes longer.

Deeper insight into the multifaceted photodynamics of a potential organic functional material emphasizing aggregation induced emission enhancement (AIEE) properties

The multifaceted photodynamics of a simple azine based organic functional molecule namely 2-((Z)-((E)-(pyren-1-ylmethylene)hydrazono)methyl)quinolin-8-ol (PHQ) emphasizing its brilliant fluorescence emission redemption properties in aggregation state (AIEE) have been primarily explored through absorption and steady state emission techniques. The governing role of photo-induced electron transfer (PET) rates and active intramolecular motions of non-interacting PHQ monomers at lower water fraction comprising mixed solvent systems have been identified to be the prime reasons for non-radiative annihilation of photoexcited states. The transition from weakly emissive to highly emissive state has been substantiated through elaborate study using time-resolved photoluminescence (TRPL), fluorescence quantum yield and variation of external control experiments. In the current study, the increased rotational relaxation time of aggregated hydrosol, responsible for AIEE, is investigated using time-resolved anisotropy measurement (TRAM) of different PHQ microenvironments, which is unprecedented to the best of our knowledge in AIEE research. Interestingly, the high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) image shows one dimensionally grown molecular entity of a single nano-sheet like structure of PHQ, which is a unique observation. The average particle size of PHQ aggregates is also increased from 84.5 nm to 814 nm corresponding to 10% and 90% fw (water volume %) system respectively. The energy-dispersive X-ray spectroscopy (EDX) has also been employed, for the first time in AIEE research, which reveals a gradual increase in the amount of carbon within the aggregated microstructure with addition of water. The present molecular system PHQ, being a molecular rotor system, provides future prospect for probing local microenvironmental viscosities within biological systems.

Reprintable paper realized employing ZnO-based photocatalytic color conversion of dyes

The invention of paper as a writing material greatly promoted the development and spread of civilization. However, its large-scale production and utilization has also brought about huge environmental and sustainability concerns. It is desirable to develop a strategy for paper that can be used in a reprintable manner. In this work, ZnO-based photocatalytic reactions have been applied in preparing a reprintable paper that works through the color conversion of methylene blue. The resulting paper does not require additional ink and can be repeatedly printed for 20 cycles keeping over 77% of the initial contrast ratio. The reprintable raw materials can be retained for more than 2 months in the ambient environment. A fast color-switching time of about 10 s has been achieved, which can be attributed to the high photo-induced electron transfer rate from the ZnO to the dyes.

Solvent-Mediated Activation/Deactivation of Photoinduced Electron-Transfer in a Molecular Dyad.

Herein is presented a molecular dyad comprised of a [Ru(bpy)3]2+ photosensitizer and an anthraquinone (AQ) acceptor coupled by an ethynyl linker ([Ru(bpy)2(bpy-cc-AQ)]2+) in which activation/deactivation of photoinduced electron-transfer from the [Ru(bpy)3]2+ photosensitizer to the AQ acceptor is achieved and characterized as a function of the dielectric constant and hydrogen-bond donating ability of the solvent used. It is demonstrated that the rate of photoinduced electron-transfer can be modulated over several orders of magnitude (105-1011 s-1) by choice of solvent. Nanosecond transient absorption spectra are dominated by MLCT signals and exhibit identical decay kinetics to the corresponding emission signals. Ultrafast transient absorption and time-resolved infrared spectroscopies provide direct evidence for the formation of the charge-separated (CS) state and rapid (on the order of a few picoseconds) establishment of an excited-state pseudoequilibrium.

Photoinduced reactions between naphthoquinone and N,N,N′,N′-tetramethyl-p-phenylenediamine in the mixture of ionic liquid [BPy][NTf2] and acetonitrile studied by transient spectroscopy

Effects of the pyridinium ionic liquid N-butylpyridinium bis((trifluoromethyl)sulfonyl)imide ([BPy][NTf2]) on the photolysis behaviors of 1,4-naphthoquinone (NQ) in the acetonitrile solutions have been investigated by using nanosecond transient absorption techniques. When [BPy][NTf2] existed in the solution, the triplet 3NQ⁎ decayed more slowly and its half lifetime became longer. The photoinduced electron transfer rate constants of NQ and N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) in the presence of [BPy][NTf2] were lower than those measured in acetonitrile, but of the same order of magnitude as estimated diffusion controlled rate constant. This finding suggests that [BPy][NTf2] could act as an appropriate solvent for electron transfer reactions. The photoinduced electron transfer reaction rate was determined not only by the viscosity but also by the microstructure of the solvent.

An Abrupt Change of Configuration of Surface Ligands Affects the H2 Production Efficiency of Mediator-Based CdS Nanorod/ Hydrogenase Assemblies

Assemblies of inorganic nanocrystals and natural enzymes are promising systems that combine both the unique and tunable photophysical properties of nanocrystals as well as the high catalytic efficiency and selectivity of bioreaction centers. The key challenge in design of these assemblies is to favor the electron/energy transfer (ET) between the abiotic and biotic materials while retarding the undesired charge recombination. The solution to this challenge relies on both rational design of materials with proper energetic and other physical properties, and, equally important if not more so, the surface condition of each component and the configuration of their assemblies. In this study, we investigate a recently developed nanorod and NiFe hydrogenase (H2ase) assemblies which utilize a redox-mediated approach to shuttle the electron transfer between the nanorods and the H2ase enzymes with an impressive H2 production quantum yield up to 77 %.1 We study the impact of alkyl chain lengths of a common type of capping ligand for nanocrystals, mercaptoalkylcarboxylate, on the H2 production quantum yield of the system and elaborate the ligand’s impact on the underlying ET transfer between NRs and the electron acceptors. We observed the existence of an abrupt decrease of the quantum yield for H2 production of the system when increasing the alkyl chain length of the ligands from n= 7 to 10 (35 % and 12 %, respectively), whereas only a minor performance decrease is observed when n is below 7 (35 % and 42 % for n=7 and 2, respectively). These results are further shown in good agreement with the sudden decrease of the yield of the reduced mediator, propyl-bridged 2-2’-bipyridinium (PDQ2+), during the steady-state photoreduction experiments, suggesting that generation efficiency of the redox equivalents control the overall efficiency of the current redox-mediated systems. Further transient spectroscopic measurements revealed that the intrinsic ET transfer rates from the NR to the mediator PDQ are all on the order of 108 s-1 regardless of the length of the capping ligands. Instead, the amount of the average surface attached PDQ2+ molecules decreases dramatically when increasing the length of n above 7, with a saturated surface coverage of σ=40 to σ =0.5 for n=2 and n= 7, respectively. These results cannot be explained by the commonly perceived ligand length dependent ET transfer by tunneling through a barrier: k = exp (- ) on the nanorod surface, with the distance dependent constants, , reported to between 0.3 to 0.8 Å-1.2,3 Instead, these results are rationalized by the accessibility of CdS surface to electron acceptors, probably due to the change of the ligand configuration from the disordered to ordered phases. These results characterize quantitively the efficiency limiting step in the mediator based CdS nanorod/Hydrogenases assemblies, demonstrate impact of configurational arrangements of ligands on NR surface on its ET behavior, and therefore are important for the design of biotic and abiotic systems for various applications. Acknowledgment Wenxing Yang acknowledges the financial support from the Swedish Research Council for an International Postdoc Fellowship. Reference (1) Chica, B.; Wu, C. H.; Liu, Y.; Adams, M. W. W.; Lian, T.; Dyer, R. B. Balancing Electron Transfer Rate and Driving Force for Efficient Photocatalytic Hydrogen Production in CdSe/CdS Nanorod-[NiFe] Hydrogenase Assemblies. Energy Environ. Sci. 2017, 10 (10), 2245–2255. (2) Tagliazucchi, M.; Tice, D. B.; Sweeney, C. M.; Morris-Cohen, A. J.; Weiss, E. A. Ligand-Controlled Rates of Photoinduced Electron Transfer in Hybrid CdSe Nanocrystal/Poly(Viologen) Films. ACS Nano 2011, 5 (12), 9907–9917. (3) Wilker, M. B.; Utterback, J. K.; Greene, S.; Brown, K. A.; Mulder, D. W.; King, P. W.; Dukovic, G. Role of Surface-Capping Ligands in Photoexcited Electron Transfer between CdS Nanorods and [FeFe] Hydrogenase and the Subsequent H 2 Generation. J. Phys. Chem. C 2018, 122 (1), 741–750. Figure 1

Carbonic anhydrase CAH3 supports the activity of photosystem II under increased pH

The lumenal carbonic anhydrase (CA) CAH3 from green alga Chlamydomonas reinhardtii is the only one CA identified so far in close association with the photosystem II (PSII) multi-subunit protein complex. It was proposed earlier, that CAH3 could facilitate the H+ removal from the active center of the PSII water-oxidizing complex (WOC) under the light, thereby increasing its activity. In the present work, using PSII enriched membranes from the wild type of C. reinhardtii and from the CAH3-deficient mutant cia3, we demonstrate, that the suppression of the photosynthetic activity of PSII by increased pH is more pronounced in preparations from cia3 as compared to the wild type. Experiments with CA inhibitors show that the activity of CAH3 supports the function of PSII and prevents its irreversible inactivation under light upon increased pH. The photosynthetic activity of PSII from cia3 can be restored to the wild type level upon increased pH if an excess of HCO3– is added. These findings testify that the main role of CAH3 in the vicinity of PSII is the acceleration of the HCO3– dehydration reaction. Measurements of the photoinduced electron transfer rate in PSII from water or from an artificial electron donor indicate, that CAH3 has a direct influence on the WOC function. Based on the data obtained in this work we conclude, that in vivo CA-activity of CAH3 may support the photosynthetic activity of PSII at increased pH in the thylakoid lumen and can be observed under the dark to light transition.

Synthesis, spectral and redox properties of closely spaced pyrrole-β-position-linked porphyrin-fullerene dyads

Two free base meso-tetraphenylporphyrin-fullerene dyads, H2PMe-C60, H2POMe-C60, and their zinc complexes, ZnPMe-C60 and ZnPOMe-C60, which the para positions of the meso-tetrasubstituted phenyl groups of the porphyrin core were substituted by methyl(-Me) and methoxyl(-OMe) groups respectively, were synthesized. The porphyrin unit in the synthesized dyads is directly linked to the fullerene entity through the pyrrole-β- position rather than through the traditionally meso-substituted phenyl group, which may be more favorable for electron communication between the donor and the acceptor. They are fully characterized by mass spectrometry, nuclear magnetic resonance, infrared spectroscopy and ultraviolet visible spectroscopy. Experimental results obtained from steady-state fluorescence spectroscopy and cyclic voltammetry show that the coordination of the zinc ions lead to an increase in the singlet excited state energy of the metallated porphyrin unit by about 0.15 eV, and to a reduce in the HOMO level and in the HOMO-LUMO energy gap. The molecular reorganization energy decreases after the electron-donating groups of -Me or -OMe attaching to the para position of the meso-phenyl group of the porphyrin moiety. The results of the energy calculations show that photoinduced electron transfer is thermodynamically favorable for the synthesized porphyrin-C60 dyads. There exists a competition between the photoinduced electron transfer and energy transfer processes from the first singlet excited state of porphyrin core to fullerene moiety. The photoinduced electron transfer rate constant of the dyads were calculated according to Marcus theory. The results indicate that the coordination of metal zinc ions lead to great increase in the electron transfer rate constant. Further, the photoinduced electron transfer rate constant increases in the order ZnP-C60, ZnPMe-C60, ZnPOMe-C60.

Comparative Study on the Mechanism of Photoinduced Electron Transfer from Tryptophan 168 to Excited Flavin in T169S and Wild-type Pyranose 2-Oxidase

The rates of photoinduced electron transfer (ET) from Trp168 to the excited isoalloxazine (Iso*) in the pyranose 2-oxidase (P2O) with T169S mutation were studied using ET theory by fitting structural properties calculated from molecular dynamics simulation to the reported fluorescence lifetimes. The obtained ET rates and related physical quantities were compared to those reported for the wild-type (WT) P2O. Experimental fluorescence lifetimes of Iso in T169S have two components of 92–240 fs (depending on the emission wavelength) and 15 ps (independent of the emission wavelength). One of the four T169S subunits (Sub C) displayed a low rate, and the other three (Sub A, B, and D) had high rates. Mean ET rates of the fast components were ca. 10 ps–1 at 480 nm, 7 ps–1 at 500 nm, and 4.2 ps–1 at 530, 555, and 580 nm, which were lower than the reported rates in the WT P2O of ca. 17 ps–1 at 480 nm, 14 ps–1 at 500 nm, 9 ps–1 at 530 and 555 nm, and 11 ps–1 at 580 nm, while the rate for the slow component in T169S (...

In situ synthesis and visible-light photocatalytic application of CdTeSe@TiO2 nanotube composites with high electron transfer rate

High quality ternary-alloyed CdTeSe quantum dots (QDs) have been synthesized via a simple one-pot approach in aqueous phase. CdTeSe QDs show an average size of 3.0nm with good crystallinity, excellent monodispersity and relatively narrow size distribution. TiO2 nanotubes (TNTs) were prepared by hydrothermal method with larger specific surface area (364.2m2g−1), and CdTeSe@TNTs were synthesized by in situ process. The absorption edge of CdTeSe@TNTs is red shifted significantly toward 697nm. After sensitized with CdTeSe, the photoluminescence (PL) emission of CdTeSe@TNTs is significantly quenched, and the fluorescence lifetime of the composites is drastically decayed from 105.82ns to 0.13ns with a high photoinduced electron transfer rate (ket=7.98×109s−1) because of their high matchable lattice constant. In addition, under visible-light irradiation, the photocatalytic efficiency of rhodamine B (RhB) with CdTeSe@TNTs reaches 90% for 80min. And the photocatalytic reaction rate constant for CdTeSe@TNTs is 0.0272min−1, which is 5.4 and 3.4 times larger than that of pure TNTs and CdTeSe QDs, respectively. It is due to the broad visible absorption of CdTeSe@TNTs and the faster photoinduced electron transfer from CdTeSe QDs to TNTs.

Design of Ruthenium Biimidazole-Anthraquinone Dyads to Demonstrate Photoinduced Electron Transfer: Combined Experimental and DFT/TD-DFT Investigations

A Biimidazole-anthraquinone ligand has been utilized in this paper to synthesize a new family of Ru(II) complexes capable of demonstrating intramolecular electron transfer from excited *[Ru(ppy)]2+ fragment to the 9,10-anthraquinone moiety upon excitation at their MLCT bands. The electronic properties of the dyads were fine-tuned by varying the coligand in the complexes. All the complexes were thoroughly characterized by standard analytical tools and spectroscopic techniques. X-ray crystal structure of a representative complex (2) was also been determined and found to crystallize in the monoclinic space group P-1. An attempt was made to assess detailed energetics and the rates of photoinduced intramolecular electron transfer in the complexes. Finally, computation works employing density functional theory (DFT) and time-dependent density functional theory (TD-DFT) were also carried out to investigate the electronic structures of the complexes as well as proper assignment of experimentally observed photo-redox behaviors.