Charge Transfer Transitions Research Articles

Photophysics of meta- and para-nitrophenolate. I. The role of configuration, microsolvation, and solvation on the charge transfer transition.

The structure of the first five singlet excited electronic states of meta-nitrophenolate (m-NP) and para-nitrophenolate (p-NP) is investigated here in the gas phase, micro-solvent, and bulk solvent environments. The first excited state (S1) of m-NP was found to be a charge transfer state in the gas phase, whereas that of p-NP is a ππ* state. A stronger coupling between the donor and acceptor molecular orbitals in p-NP leads to a higher excitation energy of the S1 state as compared to m-NP. An examination of the topography of the potential energy surfaces reveals low energy conical intersections of the S1 state with the S2 and S3 states in p-NP. Such conical intersections in m-NP are located at higher energies relative to the S1 state minimum. Repulsion between the S1(1A') and S2(1A″) electronic states via the out-of-plane -NO2 torsional mode leads to a symmetrical double well topography of the S1 state of m-NP. Present results establish that while a single solvent molecule like water, methanol, and acetonitrile leads to a blue shift in the first absorption band maxima of m-NP, the electronic localization on the donor molecular orbital due to a single water molecule yields a red shift in the first absorption band of p-NP. However, the attachment of a single water molecule to the nitro site of p-NP facilitates electronic delocalization, leading to a blue shift in the S1 state excitation energy. As a result, in an aqueous medium, the first absorption band maximum was observed very near to that found in bare p-NP.

Dimerization effects on the electronic properties of candidate OLED materials for optimized performance: a quantum DFT study.

In recent years, there has been growing interest in organic light-emitting diode (OLED) materials, highlighting the importance of a thorough understanding of the key factors that influence their electronic and non-linear optical (NLO) properties. To achieve this objective, we considered five candidate OLED compounds: dibenzothio-phen-sulfone-3-yl-9-phenyl-9H-carbazole (DBTS-CzP), 9H-thioxanthene-9-one-dibenzothiophene-sulfone (TXO-CzP), spiro[fluorene-9,9-thioxanthene]-10,10-dioxide (SpDBTS-CzP), 9-[4-(diphenylphosphoryl)-2,2-dimethyl-4-biphenylyl]-9H-carbazole (mCBPPO), and N,N-bis[2-(pyridin-2-yl)phenyl]-N,N-di(n-butyl)phenylamine (DPA-2Py). We employed density functional theory (DFT) and time-dependent DFT (TD-DFT) methods to investigate how dimerization can affect their electronic and NLO characteristics. The results of electronic structure analysis, including HOMO-LUMO gaps and NLO characteristics, reveal that dimerization enhances dipole moments and polarizabilities, facilitating improved charge transfer and electronic transitions. Among the studied compounds, TXO-CzP demonstrates stable electronic properties and exhibits enhanced NLO characteristics post-dimerization-such as efficient charge mobility and superior color purity-positioning it as a promising candidate for advanced OLED applications. These findings underscore dimerized structures' potential to enhance optoelectronic device performance.

Luminescent Binuclear Pd (II) N^C^N‐Pincer Complexes With N^N Bridging Ligand

ABSTRACTTwo novel binuclear cyclometalated Pd (II) complexes with two tridentate phenylpyridine ligands and a N^N ligand were readily synthesized. Both structures were unambiguously characterized via X‐ray single crystal diffraction, nuclear magnetic resonance (NMR) spectra, and high‐resolution mass spectrometry (HRMS). The crystal structure data reveals that the Pd–Pd distances of [Pd(1,3‐di(2‐pyridyl)benzene)]2(Dpf) (DpfH = N,N′‐diphenyl formamidine) Pd1 and [Pd(1,3‐di(2‐pyridyl)benzene]2(α‐Car) (α‐CarH = α‐carboline) Pd2 measure 3.0046(3) and 3.1518(8) Å, respectively. The absorption spectra of Pd1 and Pd2 display metal–metal‐to‐ligand charge transfer (MMLCT) transitions. In the solid state, they show triplet emissions at 635 and 607 nm, respectively. While in 1 wt% PMMA film, the emission peaks are located at 602 and 571 nm, respectively. In contrast, both complexes show very weak emission in the solution state, and their maximum emission wavelengths are significantly red‐shifted. Based on their photophysical properties, the Pd1 in 1 wt% PMMA films on quartz squares was placed in different organic or acid solvents for 30 min and then was utilized to detect organic solvent vapor. The film showed unique emission quenching for the vapor of acetone.

DNA-binding properties of non-intercalating water-soluble organometallic Ir(III) luminophores.

A series of Ir(III) complexes, [Ir(C^N)2(en)]+ (where C^N = 2-phenyl-benzo[d]thiazolyl cyclometalating ligand; en = ethylene diamine), are reported with structural variation via a substituent (H, Me, OMe, Cl, OCF3) at the coordinated phenyl ring. The complexes were soluble in aqueous buffer, with solubility limits correlating inversely with the predicted logP. The complexes display efficient visible absorption at 400-500 nm (e ~ 5000 M-1 cm-1) due to charge-transfer transitions and are triplet emitters in aerated buffer (lem = 529-540 nm; lifetimes up to 0.763 ms; Fem £ 12 %). Each complex was investigated, via computational and biophysical experiments, in the context of DNA binding. According to UV-visible titrations, the cationic complexes bind to DNA with apparent affinities ranging from 6´104 to 5´105 M-1 with apparent binding site sizes between 0.4 and 1.0 base pairs.Isothermal titration calorimetry (ITC) showed that complexes [Ir(L1-3)2(en)]Cl bind to DNA in two types of binding sites, viz. a high affinity (107-108 M-1) binding site with characteristics of major groove binding and a low affinity binding site (105 M-1) with characteristics of non-specific binding to negatively charged DNA, with binding supported by hydrophobic interactions between complexes.

Intense Absorption of Phosphorescent Biscyclometalated Ir(III) Complex with Triarylborane‐Bound 2,2’‐Bipyridine Ligand

A Monocationic biscyclometalated Ir(III) complex with triarylborane‐bound 2,2′‐bipyridine was designed and synthesized, and its photophysical properties were investigated. The triarylborane–Ir(III) complex exhibited significantly enhanced absorption in the 300–400 nm region compared to pristine biscyclometalated Ir(III) complexes, attributed to contributions from π(aryl)–p(B) charge transfer (CT) and metal‐to‐ligand charge transfer (MLCT) transitions. Moreover, IrPhB retained sub‐microsecond‐scale excited‐state lifetimes comparable to the reference complexes without triarylborane moiety. These features—strong absorption in a broad visible‐light region and long‐lived excited states—highlight the high potential of IrPhB for applications in photochemical systems.

Conduction band shift and interfacial charge transfer transition by adsorbed 4-teriary butyl pyridine analogues on TiO2: A density functional theory study

Conduction band shift and interfacial charge transfer transition by adsorbed 4-teriary butyl pyridine analogues on TiO2: A density functional theory study

Photoluminescence Properties and Concentration Quenching Mechanism of Eu3+-Doped CaLa2Mo4O16 Phosphor for Red-Emitting LED.

The red-emitting Eu3+-activated CaLa2Mo4O16 phosphors have been successfully prepared at 750°C by combustion method, which was reported first time for current work. The structural, morphological, and the photoluminescence characteristics of CaLa2Mo4O16 phosphors were throughout examined. All the phosphor compositions display broad absorption bands due to O → Mo and O → Eu charge transfer (CT) transitions, along with excellent photoluminescence characteristics, including intense electric dipole transitions (7F₀ → 5D₂). The CaLa2Mo4O16:Eu3+ when excited under near UV and blue light, phosphors display intense emission of red color at 617 nm, which ascribes due to the induced electric dipole transition (5D₀ → 7F₂). At 0.5 mol%, the maximum intensity was achieved. Dipole-dipole interaction in Eu3+-Eu3+ ions causes concentration quenching mechanism. According to calculations, the sample color coordinates under 394-nm excitation were (0.586, 0.412) at 592 nm and (0.684, 0.314) at 617 nm, which are quite similar to the normal red values of (0.68, 0.34). Therefore, the synthesized phosphors show potential as red emitters for applications in phosphor-converted red light-emitting diodes.

Strong Coupling between Mn2+ Dopants and CdSe Nanoplatelets Enables Charge-Transfer Transition and Dual Emission.

Doping transitional metals into colloidal nanocrystals can significantly modify their excited-state dynamics and enrich their optical and magneto-optical functionalities. Here we synthesize Mn-doped CdSe nanoplatelets and investigate their excited-state dynamics and light-emission mechanisms. Extensive characterizations suggest that Mn2+ ions are situated near the surface-region of the nanoplatelets. The atomic thinness of nanoplatelets allows for a strong host-dopant coupling, manifested as broadband charge-transfer absorption and emission (near 575 nm) between the host valence band and the dopant d-orbitals. Photoexcitation of the host leads to rapid (a few ps) electron transfer from the conduction band to the d-orbitals, and the resultant charge-transfer state decays within a few ns not only through charge-transfer emission but also generating an excited-state species (likely Mn-Mn dimer) with a characteristic near-infrared emission. These novel photophysics and photochemistry uncovered for quasi-two-dimensional Mn-doped nanocrystals form the basis for optical, magneto-optical, and energy conversion applications using such materials.

Synthesis and spectroscopic analysis of Ba3Ca2(PO4)3F: Eu3+/Tb3+ fluorapatite structured phosphor for optical applications.

Synthesis and spectroscopic analysis of Ba3Ca2(PO4)3F: Eu3+/Tb3+ fluorapatite structured phosphor for optical applications.

A multifaceted approach to novel (E)-3-(4-bromobenzylidene)-1,8-naphthyridine-2,4(1H,3H)-dione: synthesis, biological screening, DFT and molecular docking studies

A novel (E)-3-(4-bromobenzylidene)-1,8-naphthyridine-2,4(1H,3H)-dione derivative was synthesized and evaluated for its anticancer potential. The chemical formula and structure of the synthesized derivative was obtained using different spectroscopic techniques. Molecular structure optimization of the synthesized compound was performed using B3LYP/6–311++G (d,p) level of theory. The UV–Vis spectrum showed strong charge transfer transitions (π–π*) with high extinction coefficient (0.9869). The NBO analysis showed orbital overlap between π (C2-N11) and π*(C3-C4) due to the intramolecular charge transfer. The first hyperpolarizability (β0) was found to be 47.074 × 10−30esu, showed that the molecule can be a better option for NLO applications as compared to the standard reference urea. The global reactivity descriptors were also correlated with the biological properties of the compound. The moderate activity against HeLa cell line of the synthesized compound was reflected from its IC50 value (230 μM), QTAIM framework and Reduced Density Gradient were used to describe the nature of various intermolecular interactions and showed two closed-shell interactions (O13 – H18 and O15 – H23) with calculated bond energies of −5.0828 kJ/mol and −6.1495 kJ/mol, respectively. The reactivity sites were identified by mapping the electron density into Molecular Electrostatic Potential (MEP) and indicated that in the molecule the most electrophilic sites are the nitrogen of NH and phenyl ring. Docking studies were performed to examine binding sites of the titled molecule and the total binding energy and inhibition constant of compound were found to be −7.89 Kcal/mol and 1.65 µM exhibiting good binding affinity with the protein HER2 kinase. The bioactivity scores indicated drug-likeness of the synthesized molecule.

An efficient coumarin-based thiosemicarbazone probe for ratiometric fluorescent sensing of Zn2+ and application in live cell imaging.

An efficient coumarin-based thiosemicarbazone probe for ratiometric fluorescent sensing of Zn2+ and application in live cell imaging.

Enhanced Detection of Organic Pollutants Using ReS2/ZnO/Au Ternary Surface-Enhanced Raman Spectroscopy Substrate with Multiple Charge Transfer Channels.

Persistent organic pollutants pose significant environmental and health risks, highlighting the urgent need for highly sensitive sensing technologies capable of detecting trace concentrations. In this study, we synthesized a ReS2/ZnO/Au ternary surface-enhanced Raman spectroscopy (SERS) substrate via a simple hydrothermal and reduction method based on a novel strategy that leverages multiple charge transfer channels to significantly enhance SERS performance. The unique bandgap and energy level alignment of ReS2 facilitate both excitonic resonance and charge transfer transitions. Additionally, the semiconductor ZnO acts as an efficient charge transfer mediator by borrowing energy from molecular transitions. As a result of the synergistic combination of electromagnetic and chemical enhancements, the ReS2/ZnO/Au ternary substrate demonstrates excellent versatility and high sensitivity for detecting various pollutants, including rhodamine 6G (R6G), crystal violet, malachite green, and tetracycline (TC). Notably, the detection limit for TC can reach 10-10 M, with an enhancement factor as high as 2.78 × 108. Our strategy provides comprehensive insight into SERS enhancement, offering a pathway for designing sensitive and versatile SERS systems, with significant potential for monitoring and quantitative analysis of organic pollutants.

A New Promising Silicate-Based Phosphor for Red Light and White Light Emitting Devices.

The aim of this study is to investigate the structure, particle morphology, photoluminescence, and chemical composition of materials for application in light-emitting devices. The present work primarily focuses on the synthesis and characterization of Ba₃CdSi₂O₈:RE (RE: Ce³⁺, Eu³⁺, and Dy³⁺) phosphors via the solid-state reaction method. XRD and FT-IR techniques were used to characterize the phosphors. The XRD patterns of the phosphors reveal that the peaks match those of the Ba₃Cd(SiO₄)₂ host material (PDF Card number: 00-028-0128), with no impurity peaks observed. The photoluminescence (PL) emission spectra of Ba₃CdSi₂O₈:RE (RE: Ce³⁺, Eu³⁺, and Dy³⁺) phosphors were investigated in detail. Ba₃CdSi₂O₈:Dy³⁺ phosphors show four emission bands in the blue (450-510nm), yellow (550-600nm), red (640-700nm), and deep red (740-770nm) regions. Ce³⁺-doped Ba₃CdSi₂O₈ phosphors show a broad emission band from 575nm to 700nm, with a maximum around 594nm, which is assigned to the 5d-4f transition of Ce³⁺ ions. Moreover, Ba₃CdSi₂O₈:Eu³⁺ phosphors capture excitation energy through charge transfer transitions of Eu³⁺ ions and emit at 586nm, 613nm, 653nm, and 700nm, corresponding to the 5D₀ → 7F₀, 5D₀ → 7F₂, 5D₀ → 7F₃, and 5D₀ → 7F₄ transitions of Eu³⁺ ions, respectively. The CIE color coordinates confirm that Eu³⁺ doping shifts the color toward red, while Dy³⁺ and Ce³⁺ doping result in shifts within other parts of the chromaticity space.

Synthesis, Characterization, and Photophysical Properties of Novel BODIPY and [Zn(dipyrrin)2] Complexes from an Asymmetrical Dipyrromethene Ligand

In this study, novel homoleptic BF2 and Zn (II) complexes derived from an asymmetric dipyrromethene ligand were synthesized, with their chemical structures elucidated through NMR, and HRMS techniques. The photophysical characteristics in solution were investigated utilizing UV-visible absorption and fluorescence spectroscopy. The experimental results are clarified through Density Functional Theory (DFT) calculations and electron-hole analysis. Theoretical analyses have demonstrated that, following excitation, both electrons and holes remain confined exclusively within the BODIPY core. The charge-transfer transitions were identified between reciprocal ligands, which are responsible for the redshift observed in the main absorption band, as evidenced by electron-hole analysis. The energy levels of the frontier molecular orbitals converge contingent upon the incorporation of naphthyl and p-methoxyphenyl substituents. When analyzed under an inert nitrogen atmosphere, the compounds exhibited considerable thermal stability. Despite the similarity in the TGA curves of the complexes, the formation of the homoleptic complex resulted in an enhancement in degradation temperatures. This study indicates that chromophoric dipyrromethene complexes present advantageous prospects for advancing the development of novel materials that are both photostable and thermostable, effectively integrating charge transfer with low energy within the visible and/or near-infrared spectra.

Electron–molecular vibration coupling in trimerized isostructural mixed-stack complexes (EDT-TTF-I2)2TCNQFn (n = 0, 1, 2)

Electron–molecular vibration coupling in trimerized isostructural mixed-stack complexes (EDT-TTF-I2)2TCNQFn (n = 0, 1, 2)

Through‐space electronic coupling in π‐stacked organic mixed‐valence systems: A quantitative comparison of cationic and anionic states

AbstractThis work investigates the structural characteristics, redox behavior, intervalence charge transfer (IVCT) transition, and electronic coupling of a mixed‐valence (MV) system featuring quinoidal redox centers in 4′,4″′‐(naphthalene‐1,8‐diyl)bis(4‐methyl‐[1,1′‐biphenyl]‐2,5‐dione) (2). The three‐dimensional structures of two conformers, [2_syn]•− and [2_anti]•−, were determined using density functional theory calculations. The centroid‐to‐centroid distances between the two redox centers were 3.69 Å for [2_syn]•− and 3.41 Å for [2_anti]•−, with a weighted average distance of 3.59 Å. Electrochemical methods that include cyclic voltammetry and differential pulse voltammetry revealed two closely spaced reduction potentials (−1.04 and − 1.13 V vs. Fc+/Fc). The electronic coupling between the redox centers was evaluated using two complementary approaches: the Mulliken–Hush analysis of the IVCT band obtained through the spectroelectrochemical method and partial charge resonance analysis derived from geometrical bond length variations. The results demonstrate a significant disparity in electronic coupling, with the anion radical MV system (2•−, 413 cm−1) exhibiting electronic coupling approximately one‐third weaker than the previously reported cation radical MV system (1•+, 2055 cm−1). Charge transfer rate constants (kET) between two redox centers, calculated using parameters from spectroelectrochemical measurement, revealed that charge transfer in 2•− (5.8 × 1013 s−1) is 180 times slower than in 1•+ (3.2 × 1011 s−1). These findings underscore the critical role of electronic coupling in determining charge transfer rates and highlight the pronounced advantage of hole‐type charge carriers over electron‐type carriers. The study provides valuable insights for the rational design of advanced materials in organic electronics.

Experimental and Computational Optoelectrochemical Investigation of Quinoxaline Based Charge Transfer Derivatives: Green-Orange Emissive, AIEE Active Materials.

2,3-Diphenylquinoxalin-6-yl based dyes were synthesized and characterized using 1H, 13C, HRMS and NOSEY spectroscopic technique. The comprehensive photophysical, aggregation-induced emission enhancement (AIEE) activity, electrochemical and theoretical studies of dyes explored. The intramolecular charge transfer transition (ICT) at 380-386 nm in absorption spectra suggest weak push-pull feature of dyes. Dyes show emission in green to orange region (λmax: 561-588 nm) in solvent as well as solid state. The Stokes shift of dyes is 7979-9167 cm-1. The minimal positive solvatochromism (slight variation in λemi) own by dyes, suggest environment stability of dyes in various solvent polarity. AIEE activity with good emission at solid-state make the dyes suitable candidature for solid state OLED's application. Further Dynamic Light Scattering (DLS) studies of dye 1 validate reverse correlation of emission behavior of nanoaggregate formed at high water fraction of THF-H2O mixture with its particle size. The good thermal stability of dyes reflected by decomposition temperature i.e., 221°C-357°C (292°C-372°C) for 5(10)% weight loss. The LUMO (-3.68 to -3.83 eV) of derivatives are lower than LUMO of reported n-type materials (-3.0 to -3.30 eV). Thus, photophysical with AIEE activity and electrochemical properties obtained for dyes signify suitability of it in organic electronics.

Dual Thermally Activated Delayed Fluorescence from a Single Carbazole Derivative with Multiple Charge Transfer Pathways.

Two carbazole derivatives BPA-BNC and 4BPABNC are designed and synthesized to explore the probable dual emission behavior and mechanisms. BPA-BNC contains two arylamino donors and one B-N multi-resonance (MR) segment at 3,6,9-positions of a single carbazole, while 4BPABNC has two extra arylamine donors at 1,8-positions in addition to the above substituent groups. Two compounds in polar solvents show a clear dual emission peaked at near 490 and 540 nm with high photoluminescence quantum yields of up to 98%, short delayed lifetimes and extremely small single-triplet splitting energies. The dual emissions originate from the MR and through-bond charge transfer transitions, which are supported by theoretical calculation and experimental data. The solution-processed devices based on BPA-BNC and 4BPABNC also exhibit dual emissions and achieve the maximum external quantum efficiencies (EQEs) of 13.1% and 12.7%, whereas the model MR molecule provides an EQE of 7.3% under the same device architecture.

Efficient Size-Dependent Hot Electron Transfer from Au to TiO2 Nanoparticles.

Harvesting of plasmon-induced hot carriers at the metal/semiconductor interface offers a promising and innovative avenue for solar energy conversion. However, their practical implementation is often hampered by their limited efficiencies. Herein, we have demonstrated a highly efficient plasmonic hot electron transfer with a quantum efficiency (QE) of up to 57 ± 4% from 5.25 nm Au nanoparticles (NPs) to TiO2 films under 400 nm ultrafast laser excitation. The observed hot electron transfer QEs decrease at larger particle sizes, to 20% for 9.1 nm Au, and show negligible changes with excitation wavelengths at 400, 500, and 600 nm. Analysis of the size and excitation wavelength dependent hot electron transfer QEs suggests they contain contributions of interband absorption, indirect plasmon-induced hot electron transfer (PHET), and direct plasmon-induced interfacial charge transfer transition (PICTT) pathways, and QEs of all three pathways increase at smaller Au size. Our result suggests that reducing plasmon particle sizes is a promising approach for efficient plasmonic hot-carrier extraction.

An efficient ESIPT-based ratio-/fluorimetric probe for rapid and sensitive detection of the sarin surrogate diethylchlorophosphate in solution and vapor phases.

Nerve agents are highly toxic compounds that are based on organophosphorus chemistry, and their use is banned by international treaties regarding chemical weapons. Among the various nerve agents, sarin is highly lethal and inhibits the neuronal transmission and signaling of acetylcholinesterase. This study reports a fluorescent probe, (E)-3-(((2-(1H-benzo[d]imidazole-2-yl)phenyl)imino)methyl)-2-methoxy-2H-chromen-4-ol (BPMC), that demonstrates exceptional efficiency in detecting diethylchlorophosphate (DCP), a sarin surrogate, in solution and vapor phases. The gradual addition of DCP to the probe solution leads to a turn-on photoluminescence transition from blue to cyan because of the extension of intramolecular charge transfer transition (ICT) and inhibition of the excited-state intramolecular proton transfer (ESIPT) process. The minimum levels of DCP for detection and quantification were determined to be 6.6 μM and 22 μM, respectively, in the presence of various analogous analytes. Additionally, a test kit made of strips of cellulose paper was successfully assembled for real-time application. Dip-stick and dip-vial-conical-flask analyses were demonstrated as effective tools for detecting and quantifying DCP in the vapor phase. Furthermore, a smartphone-based approach was executed for the practical application of BPMC, enabling immediate identification and quantification of DCP in actual danger scenarios. Thus, this work presents a new ratiometric fluorogenic probe for the detection of sarin surrogate with potential application in actual hazardous situations.