Lifetime Of State Research Articles

Femtosecond laser controllable annealing for color centers based on ion-implanted silicon carbide substrate

As a representative of third-generation semiconductors, silicon carbide serves as a new platform for quantum nano-optics with readable paramagnetic color centers such as silicon vacancies. The potential applications include biomedical imaging, quantum sensing and micro/nano environment detection. Color centers are usually prepared based on ion-irradiated substrates, then annealed at high temperature to increase the yield. Currently, annealing furnaces have been the main method to heat the substrate and achieve annealing of the whole sample. However, further exploration is still necessary for fine processing requirements such as specialized annealing regions with certain shapes. In this work, we applied femtosecond laser to achieve controllable annealing at micron scale, based on silicon carbide substrate after ion injection. The whole process of point, line and pattern annealing was realized. The annealing area demonstrates enhanced photoluminescence, attributed to silicon vacancy color centers. Raman and photoluminescence spectra reveal that the annealing effect is primarily influenced by the number of pulses per unit area. The mechanism of femtosecond laser annealing was introduced. Finally, the controllable annealing areas with various shapes were prepared based on the comprehensive optimal parameters (100 kHz pulse repetition frequency, 105 point annealing pulses, 10 μm/s line scanning speed). This annealing strategy demonstrates excellent stability and uniformity, as well as micron scale accuracy. Additionally, the excited state lifetime of silicon vacancy was extracted and quantified. The result means that femtosecond laser annealing enhances the optical properties and quantum application potential of color centers. This work can be further extended to other semiconductors as well as patterned modification of local surface/planes at some depth, and helpful to explore the mechanism and applications of femtosecond laser annealing.

Impact of the Peripheral Ligand Layer on the Excited-State Deactivation Mechanism of Au38S2(S-Adm)20 and Au30(S-Adm)18 (S-Adm = Adamantanethiolate) Clusters.

Gold nanoclusters are ideal fluorescent labels for biological imaging, disease diagnosis, and treatment. Understanding the origin of the photoluminescence phenomenon in ligand-protected gold nanoclusters is crucial for both basic science and practical applications. In this study, density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations were performed to study the mechanism of excited state deactivation of Au38S2(S-Adm)20 and Au30(S-Adm)18 (S-Adm = adamantanethiolate) clusters, which have similar sizes and compositions. The computational results indicate that the differences in structural symmetry and peripheral ligand layer lead to quite different excited state deactivation mechanisms and excited state lifetimes in Au38S2(S-Adm)20 and Au30(S-Adm)18. Specifically, the μ3-S atoms and bridging thiolate (SR) in the ligand layer of Au38S2(S-Adm)20 significantly suppress the structural relaxation of ligand motifs, resulting in a prolonged excited state lifetime and higher quantum yield. For the Au30(S-Adm)18, due to the symmetry forbidden and large structural relaxation of the ligand shell, a rapid nonradiative transition process resulted. This study provides new insights into how the photoluminescence of ligand-protected gold nanoclusters is influenced by their structure and symmetry.

DFT/TD-DFT study of novel triphenylamine-based dyes with azo moieties and π-spacer variations for enhanced dye-sensitized solar cell performance

This study involves a computational analysis of new D-π-A dyes obtained from triphenylamine (TPA), which contain various azo-dye components. The structural, molecular, electrical, and optical properties of these dyes were computed using Density Functional Theory (DFT) and Time-Dependent DFT, utilizing the B3LYP/6–31 G model. Our research specifically aimed to investigate the effects of incorporating different azo dye constituents in the para position of two phenyl groups of TPA. The results indicate that these alterations lead to notably broadened and red-shifted absorption spectra, as well as improved optoelectronic properties that are subject to additional tuning through the manipulation of the π-spacer. The excitation energies and HOMO-LUMO energy levels that have been estimated indicate the presence of effective electron injection and dye regeneration mechanisms. The results concerning the nonlinear optical (NLO) properties suggest that these dyes are likely to demonstrate superior performance in NLO applications. The factors encompassed in this study consist of light-harvesting efficiency (LHE), open-circuit photovoltage (VOC), electron injection driving force (ΔGinj), dye regeneration driving force (ΔGreg), excited state lifetime (τ) and reorganization energy (λtotal), which has a strong correlation with the electrical current density in a short-circuit (JSC) and DSSC's overall effectiveness. This scientific attempt contributes to the systematic advancement of efficient dyes, demonstrating the possibility for enhanced efficiency in DSSCs. Further validation of computational forecasts and advancement of renewable energy technology necessitate future experimental synthesis and testing.

New theoretical insights on the nonradiative relaxation mechanism of the core structure of mycosporines: The amino-cyclohexenone central template.

We present a comprehensive computational study describing the excited state dynamics and consequent photostability of amino-cyclohexenone (ACyO), the central template of mycosporine systems, widely recognized for their photoprotection of aquatic species. Photoexcitation to the first excited electronic state (S1, 1nπ*) of ACyO is considered an optically dark transition, while photoexcitation to the second excited electronic state (S21ππ*) is an optically bright 1ππ* transition and largely responsible for UV absorption properties of this molecule. We show that following initial photoexcitation to S2, ACyO relaxes via two competing deactivation mechanisms, each mediated by an S1/S0 conical intersection, which directs the excited state population to the electronic ground state (S0). Our abinitio computational results are supported with nonadiabatic dynamics simulation results, yielding an excited state lifetime of ∼280fs for this system in vacuo. These results explain the inherent photostability of this core structure, commonplace in a wide range of microorganisms.

Luminescent Platinum(II) Complexes with Stimuli-Responsive Flexible Lewis Pair Ligands: Spectroscopic and Computational Studies.

A series of new luminescent bimetallic platinum(II) complexes with stimuli-responsive flexible Lewis pair (FlexLP) ligands are described. The FlexLP ligands consist of a dimesitylboron Lewis acid and diphenylphosphine oxide Lewis base which are in equilibrium between the unbound open form and the Lewis adduct, controlled by the hydrogen bond donating strength of the solvent. Spectroscopic techniques and density functional theory (DFT) calculations were used to interpret the photophysics of the platinum(II) complexes. All complexes exhibit tunable absorption in the region of 300-500 nm and green to orange photoluminescence, depending on the ratio of weak (THF) to strong (MeOH) hydrogen bond donating solvent employed. Spectroscopic and computational data shows that phosphine and peripheral acetylide ligands on the platinum(II) centers have limited influence on the emission energy, indicating the emission originates from the FlexLP-dominated fluorescence. Using time-resolved transient absorption spectroscopy it is shown that the complexes undergo intersystem crossing (ISC) to the triplet excited state upon photoexcitation, and the ISC efficiency is affected by the peripheral acetylide ligands. The triplet excited state lifetime can also be manipulated by the state of the FlexLP ligand, with the closed form complexes having longer lifetimes than the open form complexes.

Investigation of transient extreme events in a mutually coupled star network of theoretical Brusselator system

In this article, we present evidence of a distinct class of extreme events that occur during the transient chaotic state within network modeling using the Brusselator with a mutually coupled star network. We analyze the phenomenon of transient extreme events in the network by focusing on the lifetimes of chaotic states. These events are identified through the finite-time Lyapunov exponent and quantified using threshold and statistical methods, including the probability distribution function (PDF), generalized extreme value (GEV) distribution, and return period plots. We also evaluate the transitions of these extreme events by examining the average synchronization error and the system’s energy function. Our findings, validated across networks of various sizes, demonstrate consistent patterns and behaviors, contributing to a deeper understanding of transient extreme events in complex networks.

Gold Coordination-Accelerated Multi-Resonance TADF Emission for Efficient Solution-Processible Ultrapure Deep-Blue OLEDs.

Multi-resonance (MR) type emitters have emerged as highly promising candidates for high-resolution organic light-emitting diodes (OLEDs). However, thermally activated delayed fluorescence (TADF) emissions with simultaneous short excited state lifetimes and ultrapure blue color (a CIEy close to 0.046 and an emission peak > 440 nm) have rarely been obtained for MR emitters. Herein, we report a design of dual gold-coordinated MR molecules to achieve efficient and short-lived ultrapure blue TADF emission. The dinuclear Au(I) complex, namely iPrAuBN, shows a narrowband deep-blue emission with a peak maximum of 448 nm and a full width at half maximum (FWHM) of 29 nm in doped film. The coordination with two Au atoms significantly shortens the delayed fluorescence lifetime to 7.8 μs in comparing with 60.6 μs for the organic analogue. Solution-processed OLED doped with iPrAuBN demonstrates an ultrapure blue electroluminescence with a peak maximum of 442 nm, a FWHM of 19 nm, Commission International de l'Éclairage (CIE) coordinates of (0.154, 0.036), and a maximum external quantum efficiency of 14.8%.

Hard X-ray nanoprobe to study the emission properties of Ce-doped YAG wafer by using XEOL and TR-XEOL

In this study, the valent state, emission properties, and decay lifetime of Ce-doped yttrium aluminum garnet (Y3Al5O12, YAG) wafer have been probed using X-ray absorption (XAS), X-ray excited optical luminescence (XEOL), and time-resolved XEOL (TR-XEOL). The XAS spectrum demonstrates that Ce ions are in the trivalent state, and the XEOL spectrum exhibits typical 5 d1-4f1(2F5/2) and 5 d1-4f1(2F7/2) transitions of Ce3+ ions, with emission peaks at ∼528 nm and 582 nm, respectively. From the TR-XEOL measurements, the decay lifetimes of 5 d1-4f1(2F5/2) and 5 d1-4f1(2F7/2) transitions are about ∼90 ns and ∼100 ns, respectively. We found that the reabsorption effects will not only make the 5 d1-4f1(2F7/2) transitions have longer decay lifetime, but also the higher emission intensity. By comparison with photoluminescence (PL) and time-resolved PL using a pulsed laser at 375 nm, we found that the emission spectra and decay lifetime of Ce-doped YAG (111) wafer are different when using X-ray irradiation. The longer decay lifetime measured by TR-XEOL compared TR-PL are caused by high X-ray dose irradiation. In addition, high X-ray doses provided by the nano-focus X-ray beam will be influenced the emission behaviors of Ce-doped YAG (111) wafer. Which phenomena have been demonstrated by using time-dependent XEOL with irradiation for 10 h. These peculiar emission behaviors observed with a hard X-ray nanoprobe may be able to provide important information on quantum technologies and scintillators used in hard X-ray detectors.

Toward Accurate Photoluminescence Nanothermometry Using Rare-Earth Doped Nanoparticles for Biomedical Applications.

ConspectusPhotoluminescence nanothermometry can detect the local temperature at the submicrometer scale with minimal contact with the object under investigation. Owing to its high spatial resolution, this technique shows great potential in biomedicine in both fundamental studies as well as preclinical research. Photoluminescence nanothermometry exploits the temperature-dependent optical properties of various nanoscale optical probes including organic fluorophores, quantum dots, and carbon nanostructures. At the vanguard of these diverse optical probes, rare-earth doped nanoparticles (RENPs) have demonstrated remarkable capabilities in photoluminescence nanothermometry. They distinguish themselves from other luminescent nanoprobes owning to their unparalleled and versatile optical properties that include narrow emission bandwidths, high photostability, tunable lifetimes from microseconds to milliseconds, multicolor emissions spanning the ultraviolet, visible, and near-infrared (NIR) regions, and the ability to undergo upconversion, all with excitation of a single, biologically friendly NIR wavelength. Recent advancements in the design of novel RENPs have led to new fundamental breakthroughs in photoluminescence nanothermometry. Moreover, driven by their excellent biocompatibility, both in vitro and in vivo, their implementation in biomedical applications has also gained significant traction. However, these nanoprobes face limitations caused by the complex biological environments, including absorption and scattering of various biomolecules as well as interference from different tissues, which limit the spatial resolution and detection sensitivity in RENP temperature sensing.Among existing approaches in RENP photoluminescence nanothermometry, the most prevalent implemented mechanisms either leverage the changes in the relative intensity ratio of two emission bands or exploit the lifetimes of various excited states. Photoluminescence intensity ratio (PLIR) nanothermometry has been the mainstream method owing to the readily available spectrometers for photoluminescence acquisition. Despite offering high temperature sensitivity and spatial resolution, this technique is restricted by tedious calibration and undesirable fluctuation in photoluminescence intensity ascribed to factors such as probe concentration, excitation power density, and biochemical surroundings. Lifetime-based nanothermometry uses the lifetime of a specific transition as the contrast mechanism to infer the temperature. This modality is less susceptible to various experimental factors and is compatible with a broader range of photoluminescence nanoprobes. However, due to relatively expensive and complex instrumentation, long data acquisition, and sophisticated data analysis, lifetime-based nanothermometry is still breaking ground with recently emerging techniques lightening its path.In this Account, we provide an overview of RENP nanothermometry and their applications in biomedicine. The architectures and luminescence mechanisms of RENPs are examined, followed by the principles of PLIR and lifetime-based nanothermometry. The in-depth description of each approach starts with its basic principle of accurate temperature sensing, followed by a critical discussion of the representative techniques, applications as well as their strengths and limitations. Special emphasis is given to the emerging modality of lifetime-based nanothermometry in light of the important new developments in the field. Finally, a summary and an outlook are provided to conclude this Account.

Excitonic optical properties in monolayer SnP2S6

Abstract Quantum confinement effect and reduced dielectric screening in two-dimensional (2D) dramatically enhance the electron–hole interactions. In this work, we use many-body perturbation theory and Bethe–Salpeter equation (BSE) to investigate the electronic and excitonic optical properties of monolayer SnP2S6. Our findings reveal that the excitonic effect dominates the optical absorption spectra in the visible light range, and the lowest-energy exciton X 0 in monolayer SnP2S6 is optically bright with the binding energy of 0.87 eV and the radiative lifetime of ∼ 10−11 s, which is highly advantageous to the photo-luminescence. Most importantly, the absence of optically forbidden states below the bright states X 0 would give rise to a high quantum efficiency of 2D SnP2S6. We also find that applied biaxial strain can further shorten the radiative lifetime of the bright states. These results imply that 2D SnP2S6 is a promising candidate for the optoelectronic devices.

Cooperative, Close and Remote Steric Effects on the Structural and Optical Properties of Copper(I) Bis‐Phenanthroline Complexes

AbstractThe synthesis as well as the structural, optical and computational characterization of seven new highly hindered homoleptic copper(I) phenanthroline complexes (namely C1–C7) is reported along with the comparison with the benchmark derivatives. Despite limited steric hindrance in direct proximity of the copper(I) coordination site, X‐ray structures show that the higher hindered derivatives of the series display a more optimal tetrahedral geometry with minimal D2 symmetry distortion. A novel remote control of the geometry, with steric hindrance away from the coordination site, leads to a favorable arrangement as demonstrated by structural and computational data. In addition, electrochemical and steady‐state and time‐resolved photophysical studies are presented which further support the beneficial effects on the ground‐state redox and excited‐state properties when both remote and close steric effects are exploited. Indeed, both an increase of the photoluminescence quantum yield and a prolongation of the excited state lifetime is observed for the highly‐substituted derivative C6 compared to benchmark counterparts on account of the reduced excited‐state flattening distortions imparted by the additional steric constraints.

Flip-Chip-Based Fast Inductive Parity Readout of a Planar Superconducting Island

The properties of superconducting devices depend sensitively on the parity (even or odd) of the quasiparticles that they contain. Encoding quantum information in the parity degree of freedom is central in several emerging solid-state qubit architectures, including in hybrid superconductor-semiconductor devices. In the latter case, accurate, nondestructive, and time-resolved parity measurements are a challenging issue. Here, we report on control and real-time parity measurement in a superconducting island embedded in a superconducting loop and realized in a hybrid two-dimensional heterostructure using a microwave resonator. To avoid microwave losses impeding time-resolved measurements, the device and readout resonator are located on separate chips, connected via flip-chip bonding, and couple inductively through vacuum. The superconducting resonator detects the parity-dependent circuit inductance, allowing for fast parity readout. We have resolved even- and odd-parity states with a signal-to-noise ratio of SNR≈3 for an integration time of 20μs and a detection fidelity exceeding 98%. The real-time parity measurement shows a state lifetime extending into the millisecond range. Our approach will lead to a better understanding of coherence-limiting mechanisms in superconducting quantum hardware and help to advance inductive-readout schemes for hybrid qubits. Published by the American Physical Society 2024

Intracellular Gold Nanocluster/Organic Semiconductor Heterostructure for Enhancing Photosynthesis.

Photosynthetic microorganisms, which rely on light-driven electron transfer, store solar energy in self-energy carriers and convert it into bioenergy. Although these microorganisms can operate light-induced charge separation with nearly 100% quantum efficiency, their practical applications are inherently limited by the photosynthetic energy conversion efficiency. Artificial semiconductors can induce an electronic response to photoexcitation, providing additional excited electrons for natural photosynthesis to improve solar conversion efficiency. However, challenges remain in importing exogenous electrons across cell membranes. In this work, we have developed an engineered gold nanocluster/organic semiconductor heterostructure (AuNC@OFTF) to couple the intracellular electron transport chain of living cyanobacteria. AuNC@OFTF exhibits a prolonged excited state lifetime and effective charge separation. The internalized AuNC@OFTF permits its photogenerated electrons to participate in the downstream of photosystem II and construct an oriented electronic highway, which enables a five-fold increase in photocurrent in living cyanobacteria. Moreover, the binding events of AuNC@OFTF established an abiotic-biotic electronic interface at the thylakoid membrane to enhance electron flux and finally furnished nicotinamide adenine dinucleotide phosphate. Thus, AuNC@OFTF can be exploited to spatiotemporally manipulate and enhance the solar conversion of living cyanobacteria in cells, providing an extended nanotechnology for re-engineering photosynthetic pathways.

Presenting a new fluorescent probe, methyl(10-phenylphenanthren-9-yl)sulfane sensitive to the polarity and rigidity of the microenvironment: applications toward microheterogeneous systems.

A molecule, methyl(10-phenylphenanthren-9-yl)sulfane (MPPS), with a straightforward structure, has been synthesized, characterized, and explored as a new fluorescent probe for microheterogeneous systems. The photophysical properties of MPPS have been studied through experimental and theoretical calculations using the range-separated hybrid functional CAM-B3LYP in conjunction with a 6-311++g(d,p) basis set. Theoretical calculations show that the freely rotating phenyl ring forms a 94° dihedral angle with the phenanthrene ring in the ground state. Experimentally found two absorption bands correspond to the n → π* and π → π* transitions supported by the frontier molecular orbital calculations. Two excited singlet states, E-1 and E-2 (the former being more stable than the latter in the gas phase), exist with dihedral angles between the phenyl and phenanthrene rings as 142° and 133°, respectively, in the gas phase. Two emitting states in a condensed medium of varying polarities are supported by the steady-state fluorescence and fluorescence intensity decay data. Emission energies, fluorescence intensities, and excited singlet state lifetimes change with the polarity of the solvents. To support that the free rotation in the molecule is responsible for these changes, the fluorescence properties of another molecule, methyl(10-(o-tolyl)phenanthren-9-yl)sulfane (MTPS), with restricted rotation of the substituted benzene, i.e., o-tolyl ring have been studied. The fast-intensity decay component of MPPS is ascribed to the conformer in the E-1 state. The molecule has proved to be an excellent polarity probe explored to determine the critical micelle concentrations (cmc) values of different surfactants, which agree well with the literature reports. Different regions of binding isotherm (specific, non-cooperative, cooperative, and massive binding) of a gemini surfactant, 12-6-12,2Br- with bovine serum albumin (BSA) have been successfully demonstrated by the steady-state and time-resolved fluorescence and fluorescence anisotropic properties of MPPS. Docking results show that MPPS resides in the hydrophobic pocket of BSA. The fluorescence quenching of BSA by MPPS reveals the location of Trp residues of BSA. Thus, a polarity and molecular rigidity-sensitive fluorescent molecule, MPPS has been presented here that can potentially be used to monitor the changes in the microenvironment of biomolecules in different processes.

Exploring the Potential of Al(III) Photosensitizers for Energy Transfer Reactions.

Three homoleptic Al(III) complexes (Al1-Al3) with different degrees of methylation at the 2-pyridylpyrrolide ligand were systematically tested for their function as photosensitizers (PS) in two types of energy transfer reactions. First, in the generation of reactive singlet oxygen (1O2), and second, in the isomerization of (E)- to (Z)-stilbene. 1O2 was directly evidenced by its characteristic NIR emission at around 1276 nm and indirectly by the reaction with an organic substrate [e.g. 2,5-diphenylfuran (DPF)] using in situ UV/vis spectroscopy. In a previous study, the presence of additional methyl groups was found to be beneficial for the photocatalytic reduction of CO2 to CO, but here Al1 without any methyl groups exhibits superior performance. To rationalize this behavior, a combination of photophysical experiments (absorption, emission and excited state lifetimes) together with photostability measurements and scalar-relativistic time-dependent density functional theory calculations was applied. As a result, Al1 exhibited the highest emission quantum yield (64%), the longest emission lifetime (8.7 ns) and the best photostability under the reaction conditions required for the energy transfer reactions (e.g. in aerated chloroform). Moreover, Al1 provided the highest rate constant (0.043 min-1) for the photocatalytic oxygenation of DPF, outperforming even noble metal-based competitors such as [Ru(bpy)3]2+. Finally, its superior photostability enabled a long-term test (7 h), in which Al1 was successfully recycled seven times, underlining the high potential of this new class of earth-abundant PSs.

Superiority of imidazolium over triazole moiety in bis-heteroleptic ruthenium(II) complex toward selective sensing of phosphates

A new phosphorescent ruthenium-based receptor, designated as Ru-1, functionalized with imidazolium as an anion-binding moiety was synthesized and characterized for selective recognition and sensing of H2PO4− and HP2O73−. The binding affinity of Ru-1 towards numerous anions was assessed using UV–visible and phosphorescent spectroscopic techniques in CH3CN solvents. Notably, phosphate and pyrophosphate exhibited superior binding constants compared to other anions, with measured binding constants (Ka) of 7.95 × 104 and 4.78 × 104 M−1 respectively. Moreover, discernible blue shifts of 25 nm and 28 nm respectively, corresponding to H2PO4− and HP2O73− and significant enhancements in photoluminescence intensities by ∼5-fold and ∼4-fold, respectively were observed with H2PO4− and HP2O73−. Despite the existence of excess other anions, Ru-1 demonstrated selectivity towards these ions, facilitating sensitive detection with a limit of detection (LOD) of 0.045 µM for H2PO4− and 0.017 µM for HP2O73−. In the presence of H2PO4−, the lifetime of Ru-1 was amplified noticeably from 0.2329 μs to 0.7914 μs, whereas exposure to HP2O73− resulted in an observed increase of 0.7465 μs. Furthermore, comparative photophysical studies revealed that the imidazolium moiety-based Ru-1 receptor outperformed the triazole-based Ru-2 receptor in terms of excited state lifetime, binding constant, and detection limit of the anions.

(Invited) Distance Dependent Electron Transfer Kinetics in Water Soluble Axially Connected Silicon Phthalocyanine-Fullerene Conjugates

The effect of donor-acceptor distance in controlling the rate of electron transfer in axially linked silicon phthalocyanine – C60 dyads has been investigated. Herein we will presented the synthesis and photophysical properties of two water soluble C60-SiPc-C60 dyads, 1 and 2, varying in their donor-acceptor distance.In previous investigation for C60-SiPc-C60 dyads where the SiPc and C60 are separated by a phenyl spacer, faster electron transfer was observed with k cs equal to 2.7 x 109 s-1 in benzonitrile. However, in the case of C60-SiPc-C60, where SiPc and C60 are separated by a biphenyl spacer, a slower electron transfer rate constant, k cs equal to 9.1 x108 s-1 was recorded. The addition of an extra phenyl spacer in 2 increased the donor-acceptor distance by ~ 4.3 Å, and consequently, slowed down the electron transfer rate constant by a factor of ~3.7. The charge separated state lasted over 3 ns, monitoring time window of our femtosecond transient spectrometer. Complimentary nanosecond transient absorption studies revealed formation of 3SiPc* as the end product and suggested that the final lifetime of charge separated state to be in the 3-20 ns range. Energy level diagram established to comprehend these mechanistic details indicated that the comparatively high-energy SiPc .+ -C60 .- charge separated states (1.57 eV) to populate the low-lying 3SiPc* (1.26 eV) prior returning to the ground state.[1]Here we will present our recent results using water soluble SiPc-C60 1-2 systems where the SiPc is substituted with pyridine units.[3]AcknowledgmentsThis work was supported by the Ministerio de Ciencia e Innovación of Spain and FEDER funds (Grants PID2020-117855RB-I00 to ASS) and National Science Foundation (Grant No. 1401188 and 2000988 to FD).References L. Martín-Gomis, S. Seetharaman, D. Herrero, P. A. Karr, F. Fernández-Lázaro, F. D’Souza, and Á. Sastre-Santos, Chem Phys. Chem., 2020, 21, 2254-2262.V. Sobrino, L. Martín-Gomis, S. Seetharaman, P. A. Karr, D’Souza, and Á. Sastre-Santos, under preparation. Figure 1

(Invited) Molecular Donor-Acceptor Systems Derived from Aromatic Heterocycle-Fused Porphyrins

Photoinduced charge separation (CS) in molecular donor-acceptor (D-A) systems is crucial for achieving efficient solar energy conversion in various applications. Despite significant efforts to develop molecular D-A systems over the past decades, it remains a challenge to bring the lifetime of the charge separation state to ms range, which is much shorter than the CS lifetime (~1 s) in natural photosynthetic systems. In this talk, a donor-acceptor system with long-lived charge-separation state (37.2 μs) will be presented. This donor-acceptor system was derived from π-extended porphyrins fused with aromatic heterocycles. Porphyrins fused with aromatic heterocycles represent one fascinating yet very challenging frontiers in chemistry and materials science.1-4 The Wang group has been engaged in developing concise and versatile synthetic and functionalization methods for π-extended porphyrins. The availability of these methods offers easy access to many π-extended porphyrins with novel functionalities.5-7 In this talk, the synthesis, characterization, and the optical and photophysical properties of π-extended porphyrins fused with 5-, 6, and 7-membered rings including 12H-benzo[f]benzo[4,5]imidazo[2,1-a]isoindole and 1,10-phenanthroline, porphyrins will also be presented. Reference Stepien, E. Gonka, M. Zyla and N. Sprutta, Chem. Rev., 2017, 117, 3479-3716.Narita, X. Y. Wang, X. Feng and K. Mullen, Chem. Soc. Rev., 2015, 44, 6616-6643.P. Lewtak and D. T. Gryko, Chem. Commun., 2012, 48, 10069-10086.K. S. Davis, A. L. Thompson and H. L. Anderson, J. Am. Chem. Soc., 2011, 133, 30-3.Hu, M. B. Thomas, W. A. Webre, A. Moss, R. G. W. Jinadasa, V. N. Nesterov, F. D’Souza and H. Wang, Angew. Chem. Int. Ed., 2020, 45 (132), 20250-20257.Moss, Y. Jang, J. Arvidson, V. N. Nesterov, F. D’Souza and H. Wang, Chem. Sci., 2022, 13, 9880 -9890.Moss, D. E. Nevonen, Y. Hu, V. N. Nesterov, V. Nemykin and H. Wang*, ACS Phys. Chem. Au, 2022, 2, 6, 468-481.

Symmetry Breaking Charge Separation in Far-Red Absorbing Bisstyryl-Bodipy Dimers

Symmetry breaking charge transfer is one of the important photo-events occurring in photosynthetic reaction centers that is responsible for initiating electron transfer leading to a long-lived charge-separated state and has been successfully employed in light-to-electricity converting optoelectronic devices. Here, we report the synthesis of far-red absorbing and emitting BODIPY-dimer to undergo symmetry-breaking charge transfer leading to charge-separated states of appreciable lifetimes in polar solvents. Compared to its monomer analog, both steady-state and time-resolved fluorescence originating from the S1 state of the dimer revealed quenching which increased with an increase in solvent polarity. The electrostatic potential map from DFT and the time-dependent DFT calculations suggested the existence of a quadrupolar type charge transfer state in polar solvents, and the singlet excited state to be involved in the charge separation process. The electrochemically determined redox gap to be smaller than the energy of the S1 state supporting thermodynamic feasibility of the envisioned symmetry-breaking charge transfer and separation. The spectrum of the charge-separated state arrived from spectroelectrochemical studies, revealing diagnostic peaks helpful for transient spectral interpretation. Finally, ultrafast transient pump-probe spectroscopy provided conclusive evidence of diabatic charge separation in polar solvents by far-red pulsed laser light irradiation. The measured lifetime of the final charge-separated states was found to be 165 ps in dichlorobenzene, 140 ps in benzonitrile, and 43 ps in dimethyl sulfoxide, revealing their significance in light energy harvesting, especially from the less-explored far-red region.

(Invited) A CNT Binding Bis(Zinc Porphyrin)Bodipy-C60 Nano Tweezer: Charge Stabilization in Supramolecular C60-Bodipy-(ZnP)2:SWCNT Hybrids

Single-wall carbon nanotubes (SWCNT) coupled with either electron donor or acceptor are promising functional structures for light energy harvesting and molecular optoelectronics applications. For building such hybrids involving SWCNTs, the p-stacking ability of large aromatic compounds is one of the commonly employed approaches.1-2 Often, the desired donor or acceptor entities are functionalized to carry one or more aromatic entities and allowed to interact with CNTs. However, due to close proximity, the role of SWCNTs in stabilizing the electron transfer product has been a challenge.3 Recently, we overcame this hurdle by employing a multi-modular approach to build donor-acceptor hybrids and successfully demonstrated charge stabilization in the presence of SWCNTs.4 In the present study, we have further improved our design by newly synthesizing a nano tweezer comprised of covalently linked BODIPY-C60 carrying two zinc porphyrin arms as shown in the figure. This compound was further allowed to interact with SWCNT(6,5) and SWCNT(7,6) to form the supramolecular C60-BODIPY-(ZnP)2:SWCNThybrids. Upon spectral, electrochemical, and computational characterization, femtosecond pump-probe spectroscopic studies were performed to establish the occurrence of photoinduced charge separation and charge stabilization. Extending the lifetime of the charge-separated states upon SWCNT binding has been successfully demonstrated in the present molecular design strategy. D’Souza, F.; Sandanayaka, A. S. D.; Ito, O. ‘SWNT-Based Supramolecular Nanoarchitectures with Photosensitizing Donor and Acceptor Molecules’ Phys. Chem. Letts. 2010, 1. 2586-2593.B. KC, G. N. Lim, and F. D’Souza, ‘Accelerated Charge Separation in Graphene Decorated Multi-Modular Tripyrene-Subphthalocyanine-Fullerene Donor-Acceptor Hybrids,’ Angew. Chem. Int. Ed. 2015, 54, 5088-5092.Barrejon, L. M. Arellano, F. D’Souza, F. Langa, ‘Bidirectional charge transfer in carbon-based hybrid nanomaterials’ Nanoscale, 2019, 11, 14978-14992.Kazemi, Y. Jang, A. Liyanage, P. A. Karr, and F. D’Souza, A Carbon Nanotube Binding Bis(pyrenylstyryl)BODIPY-C60 Nano Tweezer: Charge Stabilization through Sequential Electron Transfer, Angew. Chem. Int. Ed. 2022, 61, e202212474 (1-7). Figure 1