Photoexcitation Dynamics Research Articles

Photoexcitation Dynamics of 4-Aminopthalimide in Solution Investigated Using Femtosecond Time-Resolved Infrared Spectroscopy

Excited-state intramolecular proton transfer (ESIPT) reactions are crucial in photoresponsive materials and fluorescent markers. The fluorescent compound 4-aminophthalimide (4-AP) has been reported to exhibit solvent-assisted ESIPT in protic solvents, such as methanol, wherein the solvent interacts with 4-AP to form a six-membered hydrogen-bonded ring that is strengthened upon excitation. Although the controversial observation of ESIPT in 4-AP has been extensively studied, the molecular mechanism has yet to be fully explored. In this study, femtosecond infrared spectroscopy was used to investigate the dynamics of 4-AP in methanol and acetonitrile after excitation at 350 and 300 nm, which promoted 4-AP to the S1 and S2 states, respectively. The excited 4-AP in the S1 state relaxed to the ground state, while 4-AP in the S2 state relaxed via the S1 state without the occurrence of ESIPT. The enol form of 4-AP (Enol 4-AP) in the S1 state was calculated to be ~10 kcal/mol higher in energy than the keto form in the S1 state, indicating that keto-to-enol tautomerization was endergonic, ultimately resulting in no observable ESIPT for 4-AP in the S1 state. Upon the excitation of 4-AP to the S2 state, the transition to Enol-4-AP in the S1 state was found to be exergonic; however, ESIPT must compete with an internal conversion from the S2 to the S1 state. The internal S2 → S1 conversion was significantly faster than the solvent-assisted ESIPT, resulting in a negligible ESIPT for the 4-AP excited to the S2 state. The detailed excitation dynamics of 4-AP clearly reveal the molecular mechanism underlying its negligible ESIPT, despite the fact that it forms a favorable structure for solvent-assisted ESIPT.

Polyacid-Modulated Carrier Dynamic Behavior at the Interface of 0D/2D Heterojunctions.

Heterojunctions formed by polyoxometalates and 2D materials draw attention owing to their remarkable photoelectric and catalytic properties. However, the intrinsic mechanisms of polyoxometalates regulating the heterojunction photoelectric properties are unclear. Herein, we constructed two types of heterojunctions by integrating polyoxometalates (Keggin-type H3PW12O40 and Lindqvist-type H2W6O19) on g-C3N4 monolayers, exploring photoexcited carrier dynamics in these heterojunctions by ab initio calculations combined with nonadiabatic molecular dynamics (NAMD) simulations. Our results show that electrons and holes in H3PW12O40 on g-C3N4 monolayers relax within 583 and 760 fs, respectively. The electron-hole recombination occurs at 342 fs, faster than carrier separation, aligning with the behavior of Z-type heterojunctions. Contrarily, the H2W6O19/g-C3N4 heterojunction exhibits the typical characteristics of type II heterojunctions, with a long photogenerated carrier lifetime reaching 652 fs. These findings show tunable band alignment in polyoxometalate-supported systems by modulating polyoxometalate type, influencing hot electron dynamics, and guiding 0D/2D heterojunction design.

Dynamics of NO Release and Linkage Isomer Formation from S-Nitroso-Mercaptoethanol in Aqueous Solutions: Insights from Femtosecond Infrared Spectroscopy.

Understanding the photodynamics of S-nitroso-thiol (RSNO), an effective NO transporter in biological systems, is essential for its photochemical applications. S-nitroso-mercaptoethanol (MceSNO), a simple water-soluble RSNO, facilitates high-level quantum calculations. We investigated the photoexcitation dynamics of MceSNO in an aqueous solution, focusing on NO dissociation, recombination, and linkage isomerization using quantum calculations and femtosecond infrared spectroscopy. Upon excitation at 320 nm, MceSNO rapidly dissociates into NO and MceS radicals. Approximately 31 ± 3% of MceS reacts with unexcited MceSNO molecules, forming MceSSMce and releasing additional NO. The remaining MceS undergoes geminate recombination with NO, forming either MceSNO (41 ± 4%) or MceSON (28 ± 3%), the latter being a sulfur-ON linkage isomer observed for the first time in a room-temperature solution. MceSON isomerizes back to MceSNO in 470 ± 30 ps. The formation mechanism of MceSON was verified through a potential energy surface constructed at the CASPT2D(16,11)/cc-pVTZ level. The isomerization barrier was determined to be 3.3 ± 1.2 kcal/mol in water.

(Invited) Synthesis and Visible-Plasmonic Properties of Intermetallic Nanoparticles

The past research on inorganic nanomaterials that exhibit intrinsic localized surface plasmon resonance (LSPR) in the visible region has focused on well-disperse nanoparticles (NPs) including group 11 elements (Au, Ag, and Cu) [1]. Recent theoretical studies on photo-excited electron dynamics in Au NPs have revealed that not only the interband transition but also the screening caused by the vibrations of bound electrons by visible light are important for visible LSPR [2]. However, the correlation between the electronic and crystal structure (as a means of controlling the screening effect) remains unclear because most alloys based on group 11 elements have a face-centered cubic (fcc)-based structure. Here, we show that well-disperse spherical intermetallic Pd-based alloy NPs and Pt-based alloy NPs with non-close packed structure intrinsically exhibit LSPR absorption in the visible region.It is well known that chemical conversion of inorganic NPs via element substitution reactions, such as ion exchange reactions [3] and galvanic replacement reactions, can overcome the difficulties associated with controlling the size, shape, chemical composition, and crystal structure in conventional syntheses [4-6]. Especially, alloying enables us to drastically modulate the electronic properties of metallic NPs. The retained shape of the parent-NPs in element replacement reactions provides an opportunity to obtain non-equilibrium unique structures and even new structures of inorganic NPs. We demonstrate that various Pd-based alloy NPs with a B2 structure were synthesized by the element replacement reactions with Pd–P NPs and showed LSPR in the visible region [7]. On the other hand, we successfully synthesized pseudospherical PtIn2 intermetallic NPs with a C1 structure as uncommon types of visible plasmonic NPs [8].Consequently, we can extract the design principles of intermetallic NPs that exhibit LSPR in the visible region in terms of the crystal and electronic structures as follows. (i) The electronic structure of intermetallic NPs should be similar to that of group 11 element NPs, that is, the sp-band crossing the Fermi level and d-band edge of noble metal like Pt around the visible region. The deeper d-band edge of another base metal like indium less affects the red-shift of LSPR wavelength. (ii) The intermetallic NPs should have non-close packed structure to cause strong screening effect by a small number of d-electrons of noble metal. The intermetallic NPs, which satisfy the above two requirements, are expected to show LSPR in the visible region and serve as novel plasmonic photocatalysts [9].[1] Kawawaki, T.; Teranishi, T. et al., J. Am. Chem. Soc. 2019, 141, 8402–8406.[2] Iida, K.; Noda, M.; Ishihara, K.; Nobusada, K. J. Phys. Chem. A 2014, 118, 11317–11322.[3] Saruyama, M.; Sato, R.; Teranishi, T. Acc. Chem. Res. 2021, 54, 765–775.[4] Wu, H.-L.; Sato, R.; Teranishi, T. et al., Science 2016, 351, 1306–1310.[5] Li, Z.; Saruyama, M.; Asaka, T.; Tatetsu, Y.; Teranishi, T. Science 2021, 373, 332–337.[6] Matsumoto, K.; Sato, R.; Tatetsu, Y.; Teranishi, T. et al., Nat. Commun. 2022, 13, 1047.[7] Sato, R.; Takekuma, H.; Teranishi T. et al., to be submitted.[8] Takekuma, H.; Sato, R.; Iida, K.; Teranishi, T. et al., Adv. Sci., in revision.[9] Lian, Z; Teranishi, T. et al., J. Am. Chem. Soc. 2019, 141, 2446–2450.

Interplay between photoinduced charge and energy transfer in manganese doped perovskite quantum dots.

A comprehensive study on the photo-excited relaxation dynamics in semiconducting perovskite quantum dots (PQDs) is pivotal in realizing their extensive potential for optoelectronics applications. Among different competing photoinduced relaxation kinetics, energy transfer and charge transfer (CT) in PQDs need special attention, as they often influence the device efficacy, particularly with the donor-acceptor hybrid architecture. In this work, we explore a detailed investigation into photoinduced CT dynamics in mixed halide undoped CsPb(Br/Cl)3 and Mn2+ doped CsPb(Br/Cl)3 PQDs with a quinone molecule, p-benzoquinone (BQ). The energy level alignment of undoped PQDs with BQ allows an efficient CT, whereas Mn2+ doping reduces the CT efficiency, experiencing a competition between energy transfer from host to dopant and CT to BQ. The conductive atomic force microscopy measurements unveil a direct correlation with the spectroscopic studies by showing a significant improvement in the conductance of undoped PQDs in the presence of BQ, while an inappreciable change is observed for doped PQDs. A much-reduced transition voltage and barrier height in the presence of BQ further validate faster CT for undoped PQD than the doped one. Furthermore, Mn2+ doping in PQDs is observed to enhance their stability, showing better air and thermal stability compared to their undoped counterparts. These results reveal that doping strategy can regulate the CT dynamics in these PQDs and increase their stability, which will be beneficial for the development of desired optoelectronic devices with long-term stability.

An Effective Model for Capturing the Role of Excitonic Interactions in the Wave-Packet Dynamics of DNA Nucleobases

Investigating exciton dynamics within DNA nucleobases is essential for comprehensively understanding how inherent photostability mechanisms function at the molecular level, particularly in the context of life’s resilience to solar radiation. In this paper, we introduce a mathematical model that effectively simulates the photoexcitation and deactivation dynamics of nucleobases within an ultrafast timeframe, particularly focusing on wave-packet dynamics under conditions of strong nonadiabatic coupling. Employing the hierarchy equation of motion, we simulate two-dimensional electronic spectra (2DES) and calibrate our model by comparing it with experimentally obtained spectra. This study also explores the effects of base stacking on the photo-deactivation dynamics in DNA. Our results demonstrate that, while strong excitonic interactions between nucleobases are present, they have a minimal impact on the deactivation dynamics of the wave packet in the electronic excited states. We further observe that the longevity of electronic excited states increases with additional base stacking and pairing, a phenomenon accurately depicted by our excitonic model. This model enables a detailed examination of the wave packet’s motion on electronic excited states and its rapid transition to the ground state. Additionally, using this model, we studied base stacks in DNA hairpins to effectively capture the primary exciton dynamics at a reasonable computational scale. Overall, this work provides a valuable framework for studying exciton dynamics from single nucleobases to complex structures such as DNA hairpins.

Photoexcited Carrier Dynamics in Iodine-Doped CH3NH3PbBr3 Single Crystals.

Iodine-doped bromide perovskite single crystals (IBPSCs) have important applications in optoelectronic fields, such as in solar cells. Currently, much research has aimed to study the phase separation phenomenon and device performance improvements in IBPSCs. However, important intrinsic photoexcited carrier dynamics are often overlooked in IBPSCs. Here, we explored the photoexcited carrier dynamics in typical iodine-doped MAPbBr3 single crystals using the excitation intensity-dependent steady-state photoluminescence (PL) and time-resolved photoluminescence (TRPL) technique. We found that the trap state density changes with an increase in the amount of doped iodine. Further, we noticed that there is an influence of carrier diffusion on the photoexcited carrier dynamics, and then, we evaluated the carrier diffusion coefficients and recombination constants via numerical simulations of the PL kinetics. Consequently, we found that the electron shallow trap-related carrier behaviors substantially impacted the PL kinetics. Our results greatly facilitate a deeper understanding of the fundamental characteristics of mixed halide perovskite material.

Comprehensive study of the ultrafast photoexcited carrier dynamics in Sb2Te3–GeTe superlattices

Abstract Chalcogenide superlattices Sb2Te3-GeTe is a candidate for interfacial phase-change memory (iPCM) data storage devices. By employing terahertz emission spectroscopy and the transient reflectance spectroscopy together, we investigate the ultrafast photoexcited carrier dynamics and current transients in Sb2Te3-GeTe superlattices. Sample orientation and excitation polarization dependences of the THz emission confirm that ultrafast thermo-electric, shift and injection currents contribute to the THz generation in Sb2Te3-GeTe superlattices. By decreasing the thickness and increasing the number of GeTe and Sb2Te3 layer, the interlayer coupling can be enhanced, which significantly reduces the contribution from circular photo-galvanic effect (CPGE). A photo-induced bleaching in the transient reflectance spectroscopy probed in the range of ~1100 nm to ~1400 nm further demonstrates a gapped state resulting from the interlayer coupling. These demonstrates play an important role in the development of iPCM-based high-speed optoelectronic devices.

MesoHOPS: Size-invariant scaling calculations of multi-excitation open quantum systems.

The photoexcitation dynamics of molecular materials on the 10-100nm length scale depend on complex interactions between electronic and vibrational degrees of freedom, rendering exact calculations difficult or intractable. The adaptive Hierarchy of Pure States (adHOPS) is a formally exact method that leverages the locality imposed by interactions between thermal environments and electronic excitations to achieve size-invariant scaling calculations for single-excitation processes in systems described by a Frenkel-Holstein Hamiltonian. Here, we extend adHOPS to account for arbitrary couplings between thermal environments and vertical excitation energies, enabling formally exact, size-invariant calculations that involve multiple excitations or states with shared thermal environments. In addition, we introduce a low-temperature correction and an effective integration of the noise to reduce the computational expense of including ultrafast vibrational relaxation in Hierarchy of Pure States (HOPS) simulations. We present these advances in the latest version of the open-source MesoHOPS library and use MesoHOPS to characterize charge separation at a one-dimensional organic heterojunction when both the electron and hole are mobile.

Ultrafast Carrier Dynamics in Ba6Cr2S10 Modified by Toroidal Magnetic Phase Transition

Ba6Cr2S10 is a recently discovered magnetic material, in which the spins are aligned ferromagnetically in the ab-plane and anti-parallelly in a paired form along the c-axis. It is characterized as a quasi-one dimensional (1D) dimerized structure with a ferrotoroidic order, forming the simplest candidate toroidal magnetic (TM) order and exhibiting an anti-ferromagnetic-like transition at around 10 K. Time-resolved ultrafast dynamics investigation of the novel A–Cr–S (A: metal elements) family of quantum materials has rarely been reported. Here, we investigate the time-resolved pump-probe ultrafast dynamics of a Ba6Cr2S10 single crystal. A prominent change in the photo-excited carrier dynamics is observed at T c = 10 K, corresponding to the reported TM-paramagnetic phase transition. A potential unknown magnetic transition is also found at T * = 29 K. Our results provide new evidence for the TM magnetic transition in Ba6Cr2S10, and shed light on phase transitions in TM quantum materials.

Enhanced Charge Separation in Single Atom Cobalt Based Graphitic Carbon Nitride: Time Domain Ab Initio Analysis.

In recent years, single atom catalysts have been at the forefront of energy conversion research, particularly in the field of catalysis. Carbon nitrides offer great potential as hosts for stabilizing metal atoms due to their unique electronic structure. We use ab initio nonadiabatic molecular dynamics to study photoexcitation dynamics in single atom cobalt based graphitic carbon nitride. The results elucidate the positive effect of the doped cobalt atom on the electronic structure of GCN. Cobalt doping produces filled midgap states that serve as oxidation centers, advantageous for various redox reactions. The presence of midgap states enables the harvesting of longer wavelength photons, thereby extending the absorption range of solar light. Although doping accelerates charge relaxation overall, charge recombination is significantly slower than charge separation, creating beneficial conditions for catalysis applications. The simulations reveal the detailed microscopic mechanism underlying the improved performance of the doped system due to atomic defects and demonstrate an effective charge separation strategy to construct highly efficient and stable photocatalytic two-dimensional materials.

Time-resolved photoelectron spectroscopy of iodide-4-thiouracil cluster: The ππ* state as a doorway for electron attachment.

The photophysics of thiobases-nucleobases in which one or more oxygen atoms are replaced with sulfur atoms- vary greatly depending on the location of sulfonation. Not only are direct dynamics of a neutral thiobase impacted, but also the dynamics of excess electron accommodation. In this work, time-resolved photoelectron spectroscopy is used to measure binary anionic clusters of iodide and 4-thiouracil, I- · 4TU. We investigate charge transfer dynamics driven by excitation at 3.88eV, corresponding to the lowest ππ* transition of the thiouracil, and at 4.16eV, near the cluster vertical detachment energy. The photoexcited state dynamics are probed by photodetachment with 1.55 and 3.14eV pulses. Excitation at 3.88eV leads to a signal from a valence-bound ion only, indicating a charge accommodation mechanism that does not involve a dipole-bound anion as an intermediate. Excitation at 4.16eV rapidly gives rise to dipole-bound and valence-bound ion signals, with a second rise in the valence-bound signal corresponding to the decay of the dipole-bound signal. The dynamics associated with the low energy ππ* excitation of 4-thiouracil provide a clear experimental proof for the importance of localized excitation and electron backfilling in halide-nucleobase clusters.

Intrinsic Visible Plasmonic Properties of Colloidal PtIn2 Intermetallic Nanoparticles.

Materials that intrinsically exhibit localized surface plasmon resonance (LSPR) in the visible region have been predominantly researched on nanoparticles (NPs) composed of coinage metals, namely Au, Ag, and Cu. Here, as a coinage metal-free intermetallic NPs, colloidal PtIn2 NPs with a C1 (CaF2 -type) crystal structure are synthesized by the liquid phase method, which evidently exhibit LSPR at wavelengths similar to face-centered cubic (fcc)-Au NPs. Computational simulations pointed out differences in the electronic structure and photo-excited electron dynamics between C1-PtIn2 and fcc-Au NPs; reduces interband transition and stronger screening with smaller number of bound d-electrons compare with fcc-Au are unique origins of the visible plasmonic nature of C1-PtIn2 NPs. These results strongly indicate that the intermetallic NPs are expected to address the development of alternative plasmonic materials by tuning their crystal structure and composition.

Imaging of ultrafast photoexcited electron dynamics in pentacene nanocrystals on a graphite substrate.

Understanding molecular film growth on substrates and the ultrafast electron dynamics at their interface is crucial for advancing next-generation organic electronics. We have focused on studying the ultrafast photoexcited electron dynamics in nanoscale organic crystals of an aromatic molecule, pentacene, on a two-dimensional material of graphite substrate. Through the use of time-resolved two-photon photoelectron emission microscopy (2P-PEEM), we have visualized the ultrafast lateral evolution of photoexcited electrons. By resonantly tuning the incident photon to excite pentacene molecules, polarization-dependent 2P-PEEM has revealed that pentacene nanocrystals (sub- to several μm) on the substrate exhibit a preferential orientation, in which a molecular π-orbital contacts the substrate in a "lying flat" orientation, facilitating electron transfer to the substrate. The time-resolved 2P-PEEM captures the motion of excited electrons in a femto- to pico-second timescale, clearly imaging the ultrafast charge transfer and lateral expansion two-dimensionally on the graphite substrate. Moreover, we found that the lying-flat molecular orientation of pentacene nanocrystals is transformable into a "standing-up" one through gentle heating up to 50 °C. These experimental insights using time-resolved 2P-PEEM will be highly valuable in enhancing the photofunctionalities of organic electronic devices by controlled molecular deposition.

How do the oxygen vacancies affect the photoexcited carriers dynamics in β-Ga2O3？

β-Ga2O3 is a rising star material for solar-blind photoelectronic detectors (PDs) since its excellent properties and lower cost than GaN and SiC. However, the high density of O vacancy (VO) strongly affect the performance of devices. In this work, we investigate the effect of VOs on carrier dynamics in β-Ga2O3 and its meaningful application in solar-blind PDs by the time-dependent density functional theory (TDDFT) and nonadiabatic molecular dynamics (NAMD). We find the three inequivalent VOs (VO1, VO2, and VO3) play different roles in carrier dynamics although they all introduce deep defect states in the bandgap, which significantly shorten the lifetime (τ) of carriers. VO1 and VO3 form nonradiative recombination centers, considerably decreasing the τ from 23.10 ns to 0.12 ns and 0.11 ns, respectively. VO2 forms shallow-level defects, and the τ is 0.47 ns, which weakens the decline of the carrier compared to VO1 and VO3. Our findings provide a different angle to understand the disputation on relationship between point defects and device performance based on β-Ga2O3, and to further improve the device performance by defect engineering.

The role of surface functionalization in quantum dot-based photocatalytic CO2 reduction: balancing efficiency and stability.

Photocatalytic CO2 reduction offers a promising strategy to produce hydrocarbons without reliance on fossil fuels. Visible light-absorbing colloidal nanomaterials composed of earth-abundant metals suspended in aqueous media are particularly attractive owing to their low-cost, ease of separation, and highly modifiable surfaces. The current study explores such a system by employing water-soluble ZnSe quantum dots and a Co-based molecular catalyst. Water solubilization of the quantum dots is achieved with either carboxylate (3-mercaptopropionic acid) or ammonium (2-aminoethanethiol) functionalized ligands to produce nanoparticles with either negatively or positively-charged surfaces. Photocatalysis experiments are performed to compare the effectiveness of these two surface functionalization strategies on CO2 reduction and ultrafast spectroscopy is used to reveal the underlying photoexcited charge dynamics. We find that the positively-charged quantum dots can support sub-picosecond electron transfer to the carboxylate-based molecular catalyst and also produce >30% selectivity for CO and >170 mmolCO gZnSe-1. However, aggregation reduces activity in approximately one day. In contrast, the negatively-charged quantum dots exhibit >10 ps electron transfer and substantially lower CO selectivity, but they are colloidally stable for days. These results highlight the importance of the quantum dot-catalyst interaction for CO2 reduction. Furthermore, multi-dentate catalyst molecules create a trade-off between photocatalytic efficiency from strong interactions and deleterious aggregation of quantum dot-catalyst assemblies.

Rationalization of the light-induced electron injection mechanism in a model 1D ZnO nanowire-dye complex: insights from real-time TD-DFTB simulations.

Zinc oxide nanowires (ZnO NWs) possess a unique one-dimensional (1D) morphology that offers a direct pathway for charge transport. In this article, we present the first application of the real-time time-dependent density functional tight-binding (real-time TD-DFTB) method for a model hybrid system consisting of a catechol molecule adsorbed on a ZnO nanowire. The rationalization of the photoinduced electron injection to the 1D nanostructure is attained through quantum dynamics simulations, stressing the role of charge transfer in the new optical transitions upon dye adsorption. We provide a momentum-resolved picture of the photoexcitation dynamics, highlighting the charge accumulation in certain k-points, which could improve our understanding of these ultrafast processes. Finally, in the context of dye-sensitized solar cells (DSSCs) based on ZnO NW arrays, we provide a method to calculate the photoresponse obtaining similar results to experiments. This work paves the way towards the fast and accurate theoretical design of 1D optoelectronic nanodevices.

Nonadiabatic molecular dynamics under adiabatic representation

<sec>In this paper, we develop a nonadiabatic molecular dynamics method based on Su-Schriffer-Heeger (SSH) Hamiltonian, and this method is widely used to study the photoexcitation dynamics and polaron motion in conjugated polymers. However, in this method, the time-dependent Schrödinger equation has so far been solved in a diabatic representation, also known as site representation. In order to provide a deeper insight into the nonadiabatic molecular dynamics method, we solve the time-dependent Schrödinger equation in an adiabatic representation. The new method can directly provide the important information about the strength of nonadiabatic couplings between different molecular orbitals in the excited-state relaxation process, helping us to predict the electron and energy transfer within or between polymer chains.</sec><sec>Solving the time-dependent Schrödinger equation in an adiabatic representation is much more complicated, it is mainly because we need to calculate the nonadiabatic couplings between different molecular orbitals. In this paper, the detailed formula derivation and actual calculation process of the nonadiabatic molecular dynamics method in an adiabatic representation are given. Using this new method, we simulate three photoexcitation processes in a conjugated polymer chain, HOMO→LUMO, HOMO–1→LUMO+1 and HOMO–2→LUMO+2. We analyze in detail the time evolutions of lattice configuration for these three photoexcitation processes, and compare these results with those obtained by diabatic representation (site representation) showing that the results obtained from these two representations are consistent with each other.</sec>

Photoexcitation dynamics of azide ion bound ferric myoglobin probed by femtosecond infrared spectroscopy

AbstractThe photoexcitation dynamics of N3−‐bound ferric myoglobin (MbN3) were investigated after exciting MbN3 in D2O at 283 K with a 575 nm pulse by probing the anti‐symmetric stretching mode of the azide. Global fitting of the overall time‐resolved spectra revealed that thermal relaxation of two stretching bands proceeded with a time constant of 6 ps, and that a new absorption band formed and decayed with time constants of 0.6 and 23 ps, respectively. The new absorption near 2040 cm−1 was attributed to the high‐spin species 2.4 kJ/mol above the low‐spin species, as the excited low‐spin relaxes thermally via the high‐spin species. However, this absorption could also arise from deligated N3̄ remaining within the protein. The decay of this absorption can be interpreted as either spin transition of the high‐spin species into the low‐spin species or geminate recombination of the dissociated N3̄. The implications of both interpretations are discussed.

PLQ−sim: A computational tool for simulating photoluminescence quenching dynamics in organic donor/acceptor blends

Photoluminescence Quenching Simulator (PLQ−Sim) is a user−friendly software to study the photoexcited state dynamics at the interface between two organic semiconductors forming a blend: an electron donor (D), and an electron acceptor (A). Its main function is to provide substantial information on the photophysical processes relevant to organic photovoltaic and photothermal devices, such as charge transfer state formation and subsequent free charge generation or exciton recombination. From input parameters provided by the user, the program calculates the transfer rates of the D/A blend and employs a kinetic model that provides the photoluminescence quenching efficiency for initial excitation in the donor or acceptor. When calculating the rates, the user can choose to use disorder parameters to better describe the system. In addition, the program was developed to address energy transfer phenomena that are commonly present in organic blends. The time evolution of state populations is also calculated providing relevant information for the user. In this article, we present the theory behind the kinetic model, along with suggestions for methods to obtain the input parameters. A detailed demonstration of the program, its applicability, and an analysis of the outputs are also presented. PLQ−Sim is license free software that can be run via dedicated webserver nanocalc.org or downloading the program executables (for Unix, Windows, and macOS) from the PLQ-Sim repository on GitHub.