Time-dependent Density Functional Theory Calculations Research Articles

Ultrafast restricted intramolecular rotation in molecules with aggregation induced emission.

In this work, the ultrafast intramolecular rotation behavior of 1,1,2,3,4,5-hexaphenylsilole has been investigated in several solutions with different viscosities using femtosecond transient absorption spectroscopy combined with density functional theory and time-dependent density functional theory calculations. It is demonstrated that the nonradiative process, which competes with radiative decay, involves two main stages, namely the restricted intramolecular rotation and internal conversion processes. The intramolecular rotation depends on viscosity and presents a significant restriction. The restricted rotational rate is determined to be dozens of picoseconds. The following nonradiative process is strongly dominated by intramolecular rotation. The nonradiative decay rate will decrease with the increase in viscosity, leading to a rise in the radiative probability and photoluminous yield. These results have borne out the mechanism of ultrafast restricted intramolecular rotation of aggregation induced emission and provided a detailed photophysical picture of nonradiative processes.

A novel 5,10,15,20-tetrakis-(4-(triazol-1-yl)phenyl)porphyridine compound: Crystal structure, photophysical properties and TDDFT calculations

A novel 5,10,15,20-tetrakis-(4-(triazol-1-yl)phenyl)porphyridine compound, namely, Zn[5,10,15,20-tetrakis-(4-(triazol-1-yl)phenyl)porphyridine] (hereafter tagged as 1) was synthesized through a solvothermal reaction with mixed solvents at 413 K. The X-ray single-crystal structure of compound 1 is featured as a two-dimensional (2D) layer-like structure with the zinc ion located at the center of the 5,10,15,20-tetrakis-(4-(triazol-1-yl)phenyl)porphyridine. The macrocycle of the 5,10,15,20-tetrakis-(4-(triazol-1-yl)phenyl)porphyridine is coplanar. The zinc ion has six coordination and coordinates with three porphyridines. The photoluminescence spectra of compound 1 with DMF solution reveal that it shows upconversion red photoluminescence. The time-dependent density functional theory (TDDFT) calculation confirms that this upconversion red photoluminescence originated from the MLCT process (metal to ligand charge transfer). The CCT (Correlated Color Temperature) is 2200 K and the CIE (Commission Internationale de I’Éclairage) chromaticity coordinate is (0.6311, 0.3595) for compound 1. The UV-vis diffuse reflectance curve measured with a solid state sample reveals that compound 1 possesses a 2.75 eV band gap.

The impact of a dopant atom on the distribution of hot electrons and holes in Au-doped Ag nano-clusters.

The generation of hot carriers (HCs) through the excitation of localized surface plasmon resonance (LSPR) in metal nanostructures is a fascinating phenomenon that fuels both fundamental and applied research. In this study, we employ first principles real-time time-dependent density-functional theory (rt-TDDFT) calculations to elucidate the creation and distribution of HCs within Au-doped Ag nanoclusters: Ag11Cl3P7H21, Ag10AucoreCl3P7H21, and Ag10AusurfCl3P7H21 nanoclusters. Our findings indicate that adjustments in HC distribution are achievable through the Au dopant atom, and precise control of HC distribution is possible by manipulating the location of the Au dopant atom. When employing a Gaussian laser pulse tailored to match the LSPR frequency, a substantial accumulation of HCs in the Ag-P bond is observed. This finding suggests a weakening of the Ag-P bonds and, consequently, the initiation of bond stretching. We propose that these findings open up possibilities for tuning HCs in Au-doped chemically functionalized Ag nanoclusters.

Cellulose nanofiber-templated metal-organic frameworks for fluorescent detection of methyl parathion pesticides

Methyl parathion is a typical organophosphorus pesticide that poses threats to the global environment and human health. In this study, we developed a portable 2D sensing pad for monitoring methyl parathion based on the aggregation-induced emission (AIE) properties of an innovated hybrid material that integrates cellulose nanofibers (CNFs) with luminescent metal-organic frameworks (LMOFs). The hybrid material enhanced the flexibility and moldability of LMOFs and significantly improved the scalability of sensing material. The resulting CNF/LMOF material was shaped into a 2D pad, exhibiting fluorescent properties under UV exposure. The fluorescence of the pad was quenchable upon exposure to methyl parathion. This host-guest interaction enabled the precise quantification of the pesticide’s concentration by monitoring the intensity variation of the fluorescence at 405 nm wavelength. We further engineered these hybrid pads into a user-friendly and portable sensing prototype, and then validated them with real sample testing. Time-dependent Density Functional Theory calculations were employed to elucidate the underlying fluorescence quenching mechanism triggered by methyl parathion. This work introduces a practical and sustainable sensing platform for pesticide detection.

Electronic and Nonlinear Optical Properties of B(III)-Submonoazaporphyrin-π-Diimide Compounds: A Density Functional Theory Study.

Three hypothetical complexes were designed using diimides (PMDI, NTCDI and PTCDI) as the acceptor unit and B(III)-submonoazaporphyrin (1) as the donor unit. These complexes have smaller HOMO-LUMO energy gaps (3.39-3.96 eV) than pristine 1 (6.61 eV). Further, the energy gap can be tuned by changing the number of benzene rings of these diimides. Remarkably, these proposed complexes possess considerable first hyperpolarizabilities (β0) (4865-6921 a.u.), and the regularity of the β0 values remained the same in the gas phase and toluene solvent conditions. There is an inverse relationship between the energy gap and the polarizability/first hyperpolarizability. In addition, absorption spectra, frontier molecular orbitals, and hole electron distributions were obtained using time-dependent density functional theory calculations to emphasize the relationship between structure and properties. Ultraviolet-Visible absorption spectra reveals that all complexes show satisfying IR working regions. Further analysis of the first hyperpolarizability density reveals the nature of the excellent NLO properties of the studied systems. This study can provide valuable insights for the development of potential high-performance NLO molecules.

Theoretical design of novel fluorophores for near-infrared fluorescent probes of peroxynitrite

On the basis of the experimentally reported near-infrared (NIR) fluorescent probe for peroxynitrite anions (ONOO–) DDAO-PN (DDAO = 1,3-dichloro-7-oxygen-9,9-dimethyl-2(9H)-acridinone, PN = 4- methylene benzeneboronic acid pinacol ester, DDAO-PN connecting 7-oxygen of DDAO with 4- methylene of PN), six DDAO derivatives DDAO-Px (x = 1–6) were designed. The fluorescence response mechanism and characteristics of the DDAO-PN probe to ONOO– were explored and the molecular structures, molecular orbital, and electron transfer during excitation and emission in DDAO-PN and DDAO-Px (x = 1–6) were comparatively analyzed in detail through the density functional theory (DFT) and time-dependent DFT calculations. The significant intramolecular charge transfer (ICT) effect in DDAO-PN were found to be suppressed when PN (as the recognition domain of ONOO– in the recognition process) was removed, rendering DDAO-PN being an effective “off-on” NIR ONOO– fluorescent probe. The introduction of different electron-donating/accepting substituents in DDAO-Px significantly changed the electronic structures and thus the fluorescent properties, which finally modified the probe efficiency. This work clarifies the structure-property relationship in DDAO-Px type NIR probes and thus provides theoretical guidance for designing new NIR fluorescent probe.

Exploring Geometrical, Electronic and Spectroscopic Properties of 2-Nitroimidazole-Based Radiopharmaceuticals via Computational Chemistry Methods.

Tumor hypoxia plays an important role in the clinical management and treatment planning of various cancers. The use of 2-nitroimidazole-based radiopharmaceuticals has been the most successful for positron emission tomography (PET) and single photon emission computed tomography (SPECT) imaging probes, offering noninvasive means to assess tumor hypoxia. In this study we performed detailed computational investigations of the most used compounds for PET imaging, focusing on those derived from 2-nitroimidazole: fluoromisonidazole (FMISO), fluoroazomycin arabinoside (FAZA), fluoroetanidazole (FETA), fluoroerythronitroimidazole (FETNIM) and 2-(2-nitroimidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl)acetamide (EF5). Conformational analysis, structural parameters, vibrational IR and Raman properties (within both harmonic and anharmonic approximations), as well as the NMR shielding tensors and spin-spin coupling constants were obtained by density functional theory (DFT) calculations and then correlated with experimental findings, where available. Furthermore, time-dependent DFT computations reveal insight into the excited states of the compounds. Our results predict a significant change in the conformational landscape of most of the investigated compounds when transitioning from the gas phase to aqueous solution. According to computational data, the 2-nitroimidazole moiety determines to a large extent the spectroscopic properties of its derivatives. Due to the limited structural information available in the current literature for the investigated compounds, the findings presented herein deepen the current understanding of the electronic structures of these five radiopharmaceuticals.

Understanding the role of π-π stacking from red carbon for selective, high stable and anti-external interference detecting ferric ions and cellular imaging

The subcarboxylated carbon (C3O2) is a unique molecule that spontaneously polymerizes into highly conjugated fluorescence structures p(C3O2)n, named “red carbon”. This unique property, combined with its role as aggregation-induced emission luminogens, has allowed for a deeper exploration of their emission mechanism. Herein, both density functional theory calculations and experimental approaches to elucidate the crystal structure of π–π stacking in red carbon, thereby enhancing the fluorescence properties of p(C3O2)n polymer in its aggregated state. The time-dependent density functional theory calculations and experimental observations indicate that the fluorescence of red carbon can be quenched by ferric ions (Fe3+) and subsequently restored by ethylenediaminetetraaceticacid (EDTA). This quenching process follows first-order reaction kinetics. On the basis of the coordination to metal ions from abundant heteroatoms on red carbon, the high sensitivity, quick responsive (1 min), sensitive detection (the lowest detection limit is 0.97 μM) for the Fe3+ were realized in red carbon, which provides inspirations for the design of new turn-on probes with high stability in detecting the Fe3+ in aqueous solution. Crucially, the red carbon as a light-up fluorescence probe can be employed for the Fe3+ sensing in living cells, which enlighten a new perspective for designing non-conjugated fluorescent polymers. This innovative approach opens up new avenues for developing probes that can detect Fe3+ with high precision and reliability in complex biological environments.

Photoluminescence of Three- and Four-Coordinate Platinum(0) Phosphine Complexes

Abstract Six platinum complexes bearing monodentate phosphine ligands were prepared and their structures and photophysical properties examined. The complexes were photoluminescent in the solid state, with a maximum quantum yield of 72%. The tris(phosphine) platinum complexes displayed more red-shifted emissions than the tetrakis complexes. The nature of the emissive excited states is discussed based on the results of density functional theory and time-dependent density-functional theory calculations.

Screening drug-induced liver injury through two independent parameters of lipid droplets and peroxynitrite with a π-extended coumarin-based NIR fluorescent probe

Drug-induced liver injury (DILI) or hepatotoxicity is a significant concern for public health. However, relying on a single biomarker for early DILI diagnosis poses a high risk of false positives. In this study, we reported a near-infrared fluorescent probe (BCOU-S), which enables independent visualization of LDs status and ONOO fluctuations. BCOU-S was constructed by combining a π-extended coumarin core as the NIR fluorophore and a methyl thioether group as the ONOO recognition site. BCOU-S could emit 655 nm NIR fluorescence excited at 518 nm, with a low detection limit of 27 nM and a large Stokes shift of 137 nm. The response mechanism to ONOO was confirmed by molecular orbital density function theory (DFT) and time-dependent DFT (TD-DFT) calculations. BCOU-S monitors LDs status through co-localization, oleic acid (OA) incubation, and starvation induction experiments. It sensitively distinguishes subtle changes in ONOO induced by different drugs in DILI cell models. In the acetaminophen (APAP)-induced DILI model, BCOU-S reveals significant LDs accumulation and increase in ONOO levels, establishing a clear time-effect and dose-effect relationship. Simultaneously monitoring ONOO levels and LDs accumulation, BCOU-S proves to be a more sensitive and effective tool for early DILI prevention, effectively avoiding false positives caused by changes in a single parameter. BCOU-S is a useful tool for further monitoring early DILI development.

Optical Activity and Excitonic Characteristics of Chiral CdSe Quantum Dots.

Introduction of chirality to colloidal semiconductor quantum dots (QDs) triggers a chiroptical effect. However, there remains a knowledge gap in the mechanism of chirality transfer and amplification from molecules to QDs. By time-dependent density functional theory calculations combined with a correlated electron-hole picture, we explored the chiroptical activity of CdSe QDs decorated with different chiral monocarboxylic acids from an excitonic perspective. Our calculations showed strong circular dichroism (CD) signals in the visible region for the chiral CdSe QDs. The excitonic states with large CD originate from QDs, while the chiral molecules break the orthogonality between electric and magnetic transition dipoles, which synergistically facilitates the prominent dissymmetric effect. The considered monocarboxylic acid chiral molecules all favor the bidentate adsorption configuration of the carboxyl group on the CdSe surface, endowing an identical CD signature but distinct excitonic characteristics. These findings are crucial for the regulation of chirality and excitons in semiconductor QDs to develop excitonic devices.

Boosting photocatalytic hydrogen peroxide evolution through aerobic oxidative dehydrogenation of benzyl alcohol over amino acid hyper-cross-linked polymer in two-phase system

The fusion of photocatalytic hydrogen peroxide (H2O2) production with the generation of high-value organic compounds carries the potential to optimize the utilization of solar energy. The efficient generation and separation of products constitute indispensable elements in constructing a proficient reaction system. Herein, the photocatalytic production of H2O2 via the aerobic oxidative dehydrogenation of benzyl alcohol (BA) was realized through the application of an amino acid hyper-cross-linked polymer (H6P-HCPs) in two-phase system. The outcomes unveiled that the H6P-HCPs with 1:6 M ratio of L-phenylalanine (L-Phe) and hexaphenylbenzene (HPB) achieves the highest generation rate of H2O2 (29.26 mmol∙gcat-1∙h-1), stoichiometric amount of benzyl alcohol oxidation products were obtained as 96% benzaldehyde (23.94 mmol∙gcat-1∙h-1) and 4% benzoic acid (5.56 mmol∙gcat-1∙h-1). Time-dependent density functional theory (TDDFT) calculations illuminated that the presence of L-Phe monomers of H6P-HCPs not only facilitated electron transfer from L-Phe to HPB, capitalizing on electronegativity differentials, but also instigated the formation of O2•- while concurrently adjusting its hydrophobic nature. These factors, in concert, were instrumental in the accomplishment of this highly efficient photocatalytic process.

Ratiometric fluoroprobe based on Eu-MOF@Tb3+ for detecting tetracycline hydrochloride in freshwater fish and its application in rapid visual detection

Tetracycline hydrochloride (TCH), a prevalent antibiotic in aquaculture for treating bacterial infections, poses challenges for on-site detection. This study employed the reversed-phase microemulsion method to synthesize a uniform nano metal-organic framework (MOF) material, europium-benzene-p-dicarboxylic acid (Eu-BDC), doped with Tb3+ to form a dual-emission fluorescence probe. By leveraging the combined a-photoinduced electron-transfer (a-PET) and inner filter effect (IFE) mechanisms, high-sensitivity TCH detection in Carassius auratus and Ruditapes philippinarum was achieved. The detection range for TCH is 0.380–75 μM, with a low limit of detection (LOD) at 0.115 μM. Upon TCH binding, Eu-BDC fluorescence rapidly decreased, while Tb3+ fluorescence remained constant, establishing a ratiometric fluorescence change. Investigation into the TCH quenching mechanism on Eu-BDC was conducted using time-dependent density functional theory (TD-DFT) calculations and fluorescence quenching kinetic equations, suggesting a mixed quenching mechanism. Furthermore, a novel photoelectric conversion fluorescence detection device (FL-2) was developed and evaluated in conjunction with high-performance liquid chromatography-diode-array detection (HPLC-DAD). This is the first dedicated fluorescence device for TCH detection, showcasing superior photoelectric conversion performance and stability that reduces experimental errors associated with smartphone photography methods, presenting a promising avenue for on-site rapid TCH detection.

Removal of caffeine from aqueous and vacuum environments using Si12C12, Si11GeC12, Si11BC12 fullerenes: A DFT and TDDFT studies

Caffeine (CFI) adsorption upon the perfect, boron-doped (Si11BC12 and Si12BC11), and germanium-doped (Si11GeC12 and Si12GeC11) silicon carbide (SiC) fullerenes have been studied to assess the feasibility of caffeine removal from aqueous and vacuum environments by using density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations. The adsorption energy and charge transfer of caffeine through its nitrogen atom of the imidazole ring upon the surface of Si12C12 nano-cage is stronger than that of the oxygen atoms of the pyrimidinedione ring with moderate adsorption energy. The theoretical infrared (IR) spectrum shows that the vibrational frequency of CFI changes after interacting with the pure Si12C12 fullerene, and this change is comparable to the experimental data. According to the TDDFT method, Ultraviolet–Visible (UV–Vis) techniques reveal that the optical features of the pure, Si11BC12, Si11GeC12 fullerenes changed after interacting with CFI. The density of state (DOS) analysis confirmed that the caffeine adsorption via imidazole ring with a robust electron hybridization can be remarkably altered the electronic features of Si12C12 fullerene, being too sensitized to the binding of caffeine. The results demonstrate that CFI adsorption on Si12C12 is stronger than on Si11BC12 and Si11GeC12 fullerenes. The presence of a boron (B) atom in the Si11BC12 fullerene improves the dipole moment and optical properties as compared to the Si11GeC12 fullerene. Upon caffeine adsorption, the Si12C12 and Si12BC11 fullerenes could be promising adsorbents for caffeine removal and detection because of the strong interaction, increasing dipole moment, and short recovery time.

Near-infrared harvesting metal-free organic dyes for transparent DSSCs: A theoretical design approach

In this study, we employed density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations to optimize near-infrared (NIR) harvesting dyes, gaining deeper insights into their structure–property relationship, particularly for dye-sensitized solar cells (DSSCs). Our focus was on fine-tuning electron-donating and withdrawing groups within D-π-A metal-free organic dyes to enhance NIR absorption and achieve visually transparent DSSCs. Our research revealed a significant redshift in dyes based on isoindigo derivatives, with thiophene (TII) as the π-spacer. Dyes incorporating fluorene as the donor group effectively mitigated charge recombination rates, a key challenge in low-bandgap molecules. Notably, the TII1 dye, combining a fluorene donor with a TII π-spacer, exhibited maximum absorption at 654 nm and transmitted substantial visible light (500–600 nm), making it suitable for use in visually transparent DSSCs. These findings underscore the potential of the TII1 dye in significantly advancing the development of visibly transparent DSSCs.

Photocatalytic activity, DFT/ TD-DFT, and spectrophotometric studies of a synthesized charge transfer complex of p- toluidine with 1,2,4,5-benzenetetracarboxylic acid in various polar solvents

The hydrogen bound charge transfer (CT) complex of p-toluidine (PT) and 1,2,4,5-benzenetetracarboxylic acid (BTC) was synthesized and subsequently characterized using a range of spectrum approaches such as FTIR, TGA / DTA, SC-XRD, and spectrophotometric examinations. Crystallographic evidence suggests that a strong hydrogen bond (N+____ H----O–) connects the cation and anion. This occurs when a proton is transported from the acceptor to the donor. The FTIR spectrum displays the proton transfer band, which is the region where neither the donor (PT) nor the acceptor (BTC) exhibits any absorption. A spectroscopic analysis showed that the CT complex (CTC) containing hydrogen bond has 1:1 stoichiometry. Benesi- Heildebrand equation was used for calculating the formation constant (KCT), molar extinction coefficient (ԑCT) and also to derive values for other physical parameters, such as energy of interaction (ECT), ionization potential (ID), free energy (ΔG°), resonance energy (RN) and oscillator strength (f). Thermal testing confirms that the newly synthesized CTC is stable at room temperature. DFT (Density Functional Theory) and TD-DFT (Time-Dependent Density Functional Theory) calculations at the B3LYP/6-311G++ level of theory were used to investigate the optimized geometry of the synthesized CTC and reactants (PT and BTC), with comparable theoretical data to support the experimental results. Furthermore, employing Hershfeld surfaces and the corresponding 2D fingerprint plots, the study of intermolecular interactions that maintain the crystal packing has been carried out. We also proved the CTC's efficiency as a photocatalyst for methylene blue (MB) breakdown, achieving 81 % photodegradation under UV–Vis light for 130 min. The scavenging analysis further demonstrates that holes and hydroxyl radicals are the photochemically active species responsible for dye particle disintegration.

Biocompatible citrate-cysteine complexes of manganese as effective antioxidants: Experimental and computational studies

Many clinical studies have evaluated the ability of sulfur-containing antioxidants to prevent oxidative stress, a major cause of cancer, Parkinson's, and Alzheimer's disease. Cysteine complexes of manganese modified with citric acid were synthesized by a one-pot procedure in two molar ratios and at two different temperatures (90°C, 140°C). The synthesized complexes were studied using FT-IR, UV-Vis, NMR, and EDX. At the lower temperature, a hydrogel was formed, and a thiazolopyridine ring was formed at a temperature of 140°C which was complexed with manganese. Infrared and electronic absorption spectroscopy confirmed that manganese binding occurred via the oxygen atoms of COO. The complexes also exhibited strong fluorescence with excitation/emission peak wavelengths of 350/418 nm. The synthesized compounds showed efficient activity for superoxide scavenging (> 70%), which was evaluated by a pyrogallol autoxidation method. MTT assay studies confirmed the noncytotoxic nature of all the prepared samples. The Gaussian 09 program was used to optimize the structural configurations of the ligands and complexes based on DFT by the B3LYP/6-31+G(d) basis set. To evaluate the softness of both the ligand and the complex, an investigation of the HOMO-LUMO gaps was carried out. In addition, UV-vis spectra of Mn complexes obtained from the time-dependent DFT calculations show a strong peak in the range of 380-390 nm, which is in good agreement with our experimental findings. The results revealed that the oxygen atoms of citrate and cysteine are the most potential sites to interact with the Mn atom. Besides, the calculated average local ionization energies showed that the Mn atom is the most energetically favored and vulnerable site to an electrophilic or free radical attack.

The role of the coupling matrix elements in time-dependent density functional theory on the simulation of core-level spectra of transition metal complexes

Time-dependent density functional theory (TD-DFT) stands out as an efficient tool for computing core-level spectra in large molecules, particularly transition metal complexes. However, despite their relatively moderate computational demands, TD-DFT methods can still pose challenges for typical computations involving transition metal complexes with over a thousand basis functions. In this study, we investigate the role of the Coulomb, Hartree–Fock exchange, and exchange-correlation kernel contributions to the TD-DFT coupling matrix elements when simulating core-level spectra in transition metal complexes. Our observations reveal that the exchange-correlation kernel contribution, responsible for more than 50% of the computational time in a hybrid TD-DFT calculation, surprisingly has no discernible impact on the qualitative aspects of the calculated spectra. While the Coulomb term plays a crucial role in describing L2,3 -edge spectra, its significance becomes negligible when considering K, L 1, and M4,5 edges. In contrast, the scaled Hartree–Fock exchange is demonstrated to be the most influential term, underscoring the necessity for hybrid density functional approximations in accurately simulating core-level spectra. These trends hold irrespective of the chosen basis set and exchange-correlation functional, providing valuable insights for the development of approximate methods for incorporating two-electron interactions within the realm of core-level spectroscopies.

Automatic Prediction of Peak Optical Absorption Wavelengths in Molecules Using Convolutional Neural Networks.

Molecular design depends heavily on optical properties for applications such as solar cells and polymer-based batteries. Accurate prediction of these properties is essential, and multiple predictive methods exist, from ab initio to data-driven techniques. Although theoretical methods, such as time-dependent density functional theory (TD-DFT) calculations, have well-established physical relevance and are among the most popular methods in computational physics and chemistry, they exhibit errors that are inherent in their approximate nature. These high-throughput electronic structure calculations also incur a substantial computational cost. With the emergence of big-data initiatives, cost-effective, data-driven methods have gained traction, although their usability is highly contingent on the degree of data quality and sparsity. In this study, we present a workflow that employs deep residual convolutional neural networks (DR-CNN) and gradient boosting feature selection to predict peak optical absorption wavelengths (λmax) exclusively from SMILES representations of dye molecules and solvents; one would normally measure λmax using UV-vis absorption spectroscopy. We use a multifidelity modeling approach, integrating 34,893 DFT calculations and 26,395 experimentally derived λmax data, to deliver more accurate predictions via a Bayesian-optimized gradient boosting machine. Our approach is benchmarked against the state of the art that is reported in the scientific literature; results demonstrate that learnt representations via a DR-CNN workflow that is integrated with other machine learning methods can accelerate the design of molecules for specific optical characteristics.

Intermolecular donor-acceptor stacking to suppress triplet exciton diffusion for long-persistent organic room-temperature phosphorescence.

Controlling triplet states is crucial to improve the efficiency and lifetime of organic room temperature phosphorescence (ORTP). Although the intrinsic factors from intramolecular radiative and non-radiative decay have been intensively investigated, the extrinsic factors that affect triplet exciton quenching are rarely reported. Diffusion to the defect sites inside the crystal or at the crystal surface may bring about quenching of triplet exciton. Here, the phosphorescence lifetime is found to have a negative correlation with the triplet exciton diffusion coefficient based on the density functional theory (DFT)/time-dependent density functional theory (TD-DFT) calculations on a series of ORTP materials. For systems with a weak charge transfer (CT) characteristic, close π-π stacking will lead to strong triplet coupling and fast triplet exciton diffusion in most cases, which is detrimental to the phosphorescence lifetime. Notably, for intramolcular donor-acceptor (D-A) type systems with a CT characteristic, intermolecular D-A stacking results in ultra-small triplet coupling, thus contributing to slow triplet diffusion and long phosphorescence lifetime. These findings shed some light on molecular design toward high-efficiency long persistent ORTP.