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Photoinduced electron transfer in non-covalent free-base octaethylporphyrin and 2-nitrofluorene donor-acceptor system: A combined experimental and quantum chemical study
摘要： Photosynthetic reaction center functions through non-covalent incorporation into a well-defined transmembrane proteins. In the context of exploring photoinduced electron transfer (PET) in non-covalent donor-acceptor systems, we have investigated electron transfer from free-base octaethylporphyrin (OEP) donor to 2-nitrofluorene (2NF) acceptor in acetonitrile (ACN), a polar solvent. Steady-state and time-resolved emission spectroscopic studies in conjunction with density functional theory (DFT) calculations were employed to explore the electron transfer process. Quenching of the fluorescence emission intensity as well as fluorescence lifetime of the OEP upon excitation at the Q band of OEP at 300 K, is attributed to the PET from OEP to 2NF. Our DFT [wB97XD functional and 6-31G (d,p) basis set] calculations also support the interaction between donor and acceptor and also reveals the co-facial π-π interaction energy of ?24.6 kcal/mol with intermolecular distance b4 ?. Our results are expected to shed light on PET in non-covalent donor acceptor systems.
关键词： Marcus theory,Photoinduced electron transfer,Octaethylporphyrin,Second-order bimolecular fluorescence quenching constant,2-Nitrofluorene,DFT study by wB97XD/6-31G(d,p),Time-resolved emission spectroscopy
更新于2025-09-23 15:22:29
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Visible-Light Driven Photocatalytic Hydrogen Generation by Water-Soluble All-Inorganic Core-Shell Silicon Quantum Dots
摘要： The photocatalytic hydrogen (H2) generation by boron (B) and phosphorus (P) codoped silicon quantum dots (Si QDs) with diameters in the quantum confinement regime is investigated. The codoped Si QDs have an amorphous shell made from B, Si and P. The shell induces negative potential on the surface and makes codoped Si QDs dispersible in water. The hydrophilic shell offers enhanced stability and efficiency in the photocatalytic H2 generation and provides the opportunity to study the size dependence of the H2 generation rate. A drastic increase of the H2 generation rate with decreasing the QD size is observed. Analyses based on the Marcus theory reveal that the upper shift of the lowest unoccupied molecular orbital level of Si QDs by the quantum confinement effect is responsible for the enhanced photocatalytic activity.
关键词： silicon quantum dots,quantum confinement,Marcus theory,photocatalytic hydrogen generation
更新于2025-09-23 15:21:01
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Photoinduced Proton-Coupled Electron Transfer in Supramolecular Sn <sup>IV</sup> Di( <scp>l</scp> -tyrosinato) Porphyrin Conjugates
摘要： Proton-coupled electron transfer (PCET) plays a key role in many biological processes, and a thorough comprehension of its subtle mechanistic complexity requires the synthesis and characterization of suitable artificial systems capable of mimicking this fundamental, elementary step. Herein, we report on a detailed photophysical investigation of conjugate 1, based on a tin(IV) tetraphenylporphyrin (SnTPP) chromophore bound to two L-tyrosinato amino acids, in CH2Cl2 in combination with organic bases of different strength and the preparation of a novel conjugate 3, based on a tin(IV) octaethylporphyrin (SnOEP) in place of the tetraphenyl analogue, and its photophysical characterization in CH2Cl2 in the presence of pyrrolidine. In the case of compound 1 with all bases examined, quenching of both the singlet and triplet excited states is observed and attributed to the occurrence of concerted proton?electron transfer (CPET). Rates and quenching yields decrease with the strength of the base used, consistent with the decrease of the driving force for the CPET process. Conjugate 3 with pyrrolidine is quenched only at the triplet level by CPET, albeit with slower rates than its parent compound 1, ascribable to the smaller driving force as a result of SnOEP being more difficult to reduce than SnTPP. For both systems, the quenching mechanism is confirmed by suitable blank experiments, specific kinetic treatments, and the observation of kinetic isotope effects (KIEs). Differently from what has been previously proposed, a detailed reinvestigation of the triplet quenching of 1 with pyrrolidine shows that no long-lived radical pair state is formed, as diradical recombination is always faster than formation. This is true for both 1 and 3 and for all bases examined. The kinetics of the CPET pathways can be well described according to Marcus theory and point toward the involvement of substantial reorganization energy as typically observed for PCET processes of concerted nature.
关键词： tin(IV) porphyrin,photophysical characterization,L-tyrosinato amino acids,CPET,PCET,Proton-coupled electron transfer,kinetic isotope effects,concerted proton?electron transfer,Marcus theory
更新于2025-09-23 15:19:57
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Photoinduced electron transfer within supramolecular hemoprotein co-assemblies and heterodimers containing Fe and Zn porphyrins
摘要： Electron transfer (ET) events occurring within metalloprotein complexes are among the most important classes of reactions in biological systems. This report describes a photoinduced electron transfer between Zn porphyrin and Fe porphyrin within a supramolecular cytochrome b562 (Cyt b562) co-assembly or heterodimer with a well-defined rigid structure formed by a metalloporphyrin–heme pocket interaction and a hydrogen-bond network at the protein interface. The photoinduced charge separation (CS: kCS = 320 – 600 s–1) and subsequent charge recombination (CR: kCR = 580 – 930 s–1) were observed in both the Cyt b562 co-assembly and the heterodimer. In contrast, interestingly, no ET events were observed in a system comprised of a flexible and structurally-undefined co-assembly and heterodimers which lack the key hydrogen-bond interaction at the protein interface. Moreover, analysis of the kinetic constants of CS and CR of the heterodimer using the Marcus equation suggests that a single-step ET reaction occurs in the system. These findings provide strong support that the rigid hemoprotein-assembling system containing an appropriate hydrogen-bond network at the protein interface is essential for monitoring the ET reaction.
关键词： Hydrogen bond network,Photoinduced electron transfer,Cytochrome b562,Marcus theory,Hemoprotein assembly
更新于2025-09-19 17:15:36
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Theoretical Study on the Charge Transport Property of Thia- or Selenadiazole Compound
摘要： In this work, we carried out theoretical investigation on the charge-transporting nature of 4,11-bis-[(triisopropylsilanyl)-ethynyl]-2-thia-1,3-diaza-cyclopenta[b]anthracene (1) and 4,11-bis-[(triisopropylsilanyl)-ethynyl]-2-selena-1,3-diaza-cyclopenta[b]anthracene (2) by Marcus theory and first-principle band structure. The character of the frontier molecular orbitals, reorganization energies, transfer integrals and band structures are considered in detail. The results show that the compounds 1 and 2 are ambipolar material, both electron and hole are favor of transporting. The intermolecular π-π ineraction and S···N/Se···N interaction provide the holes and electrons transport channels. The introduction of Se atom can effectively reduce the reorganization energy and considerably improve the electron transfer integrals, thus 2 is found to be a good candidate for ambipolar semiconducting material with high mobility and balanced transport.
关键词： DFT,Marcus theory,Band structure
更新于2025-09-19 17:15:36
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Understanding resonant charge transport through weakly coupled single-molecule junctions
摘要： Off-resonant charge transport through molecular junctions has been extensively studied since the advent of single-molecule electronics and is now well understood within the framework of the non-interacting Landauer approach. Conversely, gaining a qualitative and quantitative understanding of the resonant transport regime has proven more elusive. Here, we study resonant charge transport through graphene-based zinc-porphyrin junctions. We experimentally demonstrate an inadequacy of non-interacting Landauer theory as well as the conventional single-mode Franck–Condon model. Instead, we model overall charge transport as a sequence of non-adiabatic electron transfers, with rates depending on both outer and inner-sphere vibrational interactions. We show that the transport properties of our molecular junctions are determined by a combination of electron–electron and electron-vibrational coupling, and are sensitive to interactions with the wider local environment. Furthermore, we assess the importance of nuclear tunnelling and examine the suitability of semi-classical Marcus theory as a description of charge transport in molecular devices.
关键词： Marcus theory,single-molecule junctions,electron-vibrational coupling,electron transfers,resonant charge transport,Landauer theory,Franck–Condon model,electron–electron interactions
更新于2025-09-19 17:13:59
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Excited-state proton-coupled electron transfer within ion pairs
摘要： The use of light to drive proton-coupled electron transfer (PCET) reactions has received growing interest, with recent focus on the direct use of excited states in PCET reactions (ES-PCET). Electrostatic ion pairs provide a scaffold to reduce reaction orders and have facilitated many discoveries in electron-transfer chemistry. Their use, however, has not translated to PCET. Herein, we show that ion pairs, formed solely through electrostatic interactions, provide a general, facile means to study an ES-PCET mechanism. These ion pairs formed readily between salicylate anions and tetracationic ruthenium complexes in acetonitrile solution. Upon light excitation, quenching of the ruthenium excited state occurred through ES-PCET oxidation of salicylate within the ion pair. Transient absorption spectroscopy identified the reduced ruthenium complex and oxidized salicylate radical as the primary photoproducts of this reaction. The reduced reaction order due to ion pairing allowed the first-order PCET rate constants to be directly measured through nanosecond photoluminescence spectroscopy. These PCET rate constants saturated at larger driving forces consistent with approaching the Marcus barrierless region. Surprisingly, a proton-transfer tautomer of salicylate, with the proton localized on the carboxylate functional group, was present in acetonitrile. A pre-equilibrium model based on this tautomerization provided non-adiabatic electron-transfer rate constants that were well described by Marcus theory. Electrostatic ion pairs were critical to our ability to investigate this PCET mechanism without the need to covalently link the donor and acceptor or introduce specific hydrogen bonding sites that could compete in alternate PCET pathways.
关键词： proton-coupled electron transfer,salicylate,ion pairs,ruthenium complexes,Marcus theory,excited-state
更新于2025-09-19 17:13:59
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Donor–Acceptor Distance-Dependent Charge Transfer Dynamics Controlled by Metamaterial Structures
摘要： Capability to control charge transfer dynamics in donor-acceptor molecule is important for efficient optoelectronic devices. Charge transfer dynamics is governed by thermodynamics of donor-acceptor charges in a given dielectric environment. Metamaterial structure has been shown to be able to control charge separation and charge recombination processes via nonlocal effect on dielectric permittivity for a fixed donor-acceptor distance organic film. Here, we report the influence of metamaterial structure on the donor-acceptor distance dependence of electron transfer process occurring in liquid crystalline organic semiconductor thin films. By examining charge recombination rate in three different donor-acceptor distances, it is found that the barrier height β increases from 0.084 ??1 to 0.137 ??1 by 63% in the presence of metal-dielectric multilayered metamaterial structures. Based on Marcus theory on charge transfer process, we show that the further increase of driving force for a larger donor-acceptor distance is mainly responsible for the barrier height increase in the presence of multi-layered metamaterial substrate when compared with glass substrate. This study will provide a significant step forward in enabling more efficient hybrid organic-optoelectronic devices associated with charge transfer process.
关键词： Charge transfer dynamics,Organic semiconductors,Metamaterials,Marcus Theory,Nonlocal effect
更新于2025-09-12 10:27:22
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Homogeneous Electron Transfer Reactions of Electrochemically Generated Species in Electrogenerated Chemiluminescence; 電気化学発光における電極反応の後続反応;
摘要： Electrogenerated Chemiluminescence (ECL) involves electrode reactions and the following homogeneous electron transfer reactions which resulted in a light emission. In this integrated research paper, we focused on the homogeneous electron transfer reactions to form excited states of some luminescent molecules. The Marcus theory was used to estimate ratios of the electron-transfer rate constants between a radical cation and anion to generate the lowest excited singlet and triplet states. In addition, the ECL behavior using tripropylamine as a coreactant was demonstrated by simulating the electrochemical and homogeneous electron transfer reactions with a finite element method. Although coreactants are useful to form excited species, because of complicated reactions in bulk, analyzing the ECL response such as relationship between the current-voltage and ECL intensity curves depending on the redox potentials of luminescent molecules and coreactants is quite difficult. It was shown that the simulations were very useful to understand the ECL response depending on the redox potentials of the coreactant and luminescent molecules.
关键词： Marcus theory,homogeneous electron transfer,Electrogenerated Chemiluminescence,tripropylamine,finite element method
更新于2025-09-09 09:28:46
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Tuning Photoinduced Electron Transfer Efficiency of Fluorogenic BODIPY- <i>α</i> -Tocopherol Analogues
摘要： Fluorogenic analogues of α-tocopherol developed by our group have been instrumental in monitoring reactive oxygen species (ROS) within lipid membranes. Prepared as two-segment trap-reporter (chromanol-BODIPY) probes, photoinduced electron transfer (PeT) was utilized to provide these probes with an off/on switch mechanism warranting the necessary sensitivity. Herein we rationalize within the context of Marcus theory of electron transfer how substituents on the BODIPY core and linker length joining the trap and reporter segments, tune PeT efficiency. DFT and electrochemical studies were used to estimate the thermodynamic driving force of PeT in our constructs. By tuning the redox potential over a 400 mV range, we observed over an order of magnitude increase in PeT efficiency. Increasing the linker length between the chromanol and BODIPY by 2.8 angstroms in turn decreased PeT efficiency 2.7-fold. Our results illustrate how substituent and linker choice enable “darkening” the off state of fluorogenic probes based on BODIPY fluorophores, by favoring PeT over radiative emission from the singlet excited state manifold. Ultimately, our work brings light to the sensitivity ceiling one may achieve in developing fluorogenic antioxidants analogues of α-tocopherol. The work provides general guidelines applicable to those developing fluorogenic probes based on PeT.
关键词： electrochemical studies,α-tocopherol,lipid membranes,reactive oxygen species,redox potential,photoinduced electron transfer,Marcus theory,DFT,Fluorogenic analogues,BODIPY
更新于2025-09-09 09:28:46