Spatiotemporal imaging of charge transfer in photocatalyst particles.

The water-splitting reaction using photocatalyst particles is a promising route for solar fuel production1-4. Photo-induced charge transfer from a photocatalyst to catalytic surface sites is key in ensuring photocatalytic efficiency5; however, it is challenging to understand this process, which spans a wide spatiotemporal range from nanometres to micrometres and from femtoseconds to seconds6-8. Although the steady-state charge distribution on single photocatalyst particles has been mapped by microscopic techniques9-11, and the charge transfer dynamics in photocatalyst aggregations have been revealed by time-resolved spectroscopy12,13, spatiotemporally evolving charge transfer processes in single photocatalyst particles cannot be tracked, and their exact mechanism is unknown. Here we perform spatiotemporally resolved surface photovoltage measurements on cuprous oxide photocatalyst particles to map holistic charge transfer processes on the femtosecond to second timescale at the single-particle level. We find that photogenerated electrons are transferred to the catalytic surface quasi-ballistically through inter-facet hot electron transfer on a subpicosecond timescale, whereas photogenerated holes are transferred to a spatially separated surface and stabilized through selective trapping on a microsecond timescale. We demonstrate that these ultrafast-hot-electron-transfer and anisotropic-trapping regimes, which challenge the classical perception of a drift-diffusion model, contribute to the efficient charge separation in photocatalysis and improve photocatalytic performance. We anticipate that our findings will be used to illustrate the universality of other photoelectronic devices and facilitate the rational design of photocatalysts.

A Coupled System of Ni3S2 and Rh Complex with Biomimetic Function for Electrocatalytic 1,4-NAD(P)H Regeneration.

NAD(P)H cofactor is a critical energy and electron carrier in biocatalysis and photosynthesis, but the artificial reduction of NAD(P)+ to regenerate bioactive 1,4-NAD(P)H with both high activity and selectivity is challenging. Herein, we found that a coupled system of a Ni3S2 electrode and a Rh complex in an electrolyte (denoted as Ni3S2-Rh) can catalyze the reduction of NAD(P)+ to 1,4-NAD(P)H with superior activity and selectivity. The optimized selectivity in 1,4-NADH can be up to 99.1%, much higher than that for Ni3S2 (80%); the normalized activity of Ni3S2-Rh is about 5.8 times that of Ni3S2 and 13.2 times that of the Rh complex. The high performance of Ni3S2-Rh is attributed to the synergistic effect between metal sulfides and Rh complex. The NAD+ reduction reaction proceeds via a concerted electron-proton transfer (CEPT) mechanism in the Ni3S2-Rh system, in which Ni3S2 acts as a proton and electron-transfer mediator to accelerate the formation of Rh hydride (Rh-H), and then the Rh-H regioselectively transfers the hydride to NAD+ to form 1,4-NADH. The artificial system Ni3S2-Rh essentially mimics the functions of ferredoxin-NADP+ reductase in nature.

Type-I Photodynamic Therapy Induced by Pt-Coordination of Type-II Photosensitizers into Supramolecular Complexes.

Platinum supramolecular complexes based on photosensitizers have garnered great interest in photodynamic therapy (PDT) due to Pt (II) centers as chemotherapeutic agents to eliminate tumor cells completely, which greatly improve the antitumor efficacy of PDT. However, in comparison to precursor photosensitizer ligand, the formed platinum supramolecular complexes typically exhibit inferior outcomes in terms of reactive oxygen species (ROS) generation. How to boost ROS generation in the formed platinum supramolecular complexes for enhanced PDT is an enticing yet highly challenging task. Here we report a Pt-coordination-based dimeric photosensitizer complex (Cz-BTZ-Py)2Pt(OTf)2. It is found that comparing with photosensitizer ligand Cz-BTZ-Py, the formed supramolecular complex exhibit redshifts of absorption wavelength as well as enhanced ROS generation efficiency. Moreover, type-I ROS generation (O2⋅-) is produced in the formed platinum supramolecular complexes mainly due to a reduced energy gap ΔEST resulting from exciton coupling between two photosensitizer ligands. And type-I ROS (O2⋅-) generation significantly amplifies the photodynamic therapy (PDT) outcomes. In vitro evaluation shows excellent photochemotherapy performance of (Cz-BTZ-Py)2Pt(OTf)2 nanoparticles. We anticipate this work would provide a novel approach to design type-I photosensitizers for efficient PDT.

Hydrogen Sulfide Splitting into Hydrogen and Sulfur through Off-Field Electrocatalysis.

Hydrogen sulfide (H2S), a toxic gas abundant in natural gas fields and refineries, is currently being removed mainly via the Claus process. However, the emission of sulfur-containing pollutants is hard to be prevented and the hydrogen element is combined to water. Herein, we report an electron-mediated off-field electrocatalysis approach (OFEC) for complete splitting of H2S into H2 and S under ambient conditions. Fe(III)/Fe(II) and V(II)/V(III) redox mediators are used to fulfill the cycles for H2S oxidation and H2 production, respectively. Fe(III) effectively removes H2S with almost 100% conversion during its oxidation process. The H+ ions are reduced by V(II) on a nonprecious metal catalyst, tungsten carbide. The mediators are regenerated in an electrolyzer at a cell voltage of 1.05 V, close to the theoretical potential difference (1.02 V) between Fe(III)/Fe(II) and V(II)/V(III). In a laboratory bench-scale plant, the energy consumption for the production of H2 from H2S is estimated to be 2.8 kWh Nm-3 H2 using Fe(III)/Fe(II) and V(II)/V(III) mediators and further reduced to about 0.5 kWh Nm-3 H2 when employing well-designed heteropolyacid/quinone mediators. OFEC presents a cost-effective approach for the simultaneous production of H2 and elemental sulfur from H2S, along with the complete removal of H2S from industrial processes. It also provides a practical platform for electrochemical reactions involving solid precipitation and organic synthesis.

N-Protonation as a Switch of the Twisted Excited States with ππ* or nπ* Character and Correlation with the π-Electrons Characteristic of Rotatable Bonds.

N-protonation for numerous fluorophores is widely known as an efficient switch for the fluorescence turn-on/off in acidic conditions, which has been applied in various scenarios that involve pH monitoring. Yet the universal mechanism for fluorescence regulation through N-protonation is still elusive. Herein, the excited state deactivation processes are systematically investigated for a series of nitrogen-containing fluorescent probes through theoretical approaches. Two types of mechanisms for the complex fluorescent phenomena by N-protonation are concluded: one is through the regulation for the transition to a ππ* twisted intramolecular charge transfer (TICT) state; the other one applies for the case when nonradiative decay pathway is predominant by a dark nπ* state, which is also accompanied by an evident structural twisting and can be regarded as another kind of TICT state. More generally, the formation of the TICT state is closely related to the conjugated π-electrons on the single bond that links the acceptor and donor part of fluorophores, which provides a simple strategy for evaluating the occurrence of the TICT process. The current contributions can bring novel insights for the rational design of functional fluorophores that involve TICT process in the excited states.

Unraveling the Mechanism of ACQ-to-AIE Transformation of Fluorescein Derivatives.

Although fluorescein derivatives have excellent properties and strong practicability, they are typical aggregation-induced quenching (ACQ) molecules, which are not conducive to working in the solid state. Recently, the fluorescein derivative Fl-Me with aggregation-induced emission (AIE) property was synthesized, which brought a new dawn for the research and development of fluorescein-based materials. In this study, the AIE mechanism of Fl-Me was investigated based on time-dependent density functional theory and the ONIOM method. The results revealed that an effective dark-state deactivation pathway leads to the fluorescence quenching of Fl-Me in a solution environment. Accordingly, the AIE phenomenon originates from the closure of the dark-state quenching channel. It is worth emphasizing that we found that the carbonyl group of molecular Fl-Me has intermolecular hydrogen bonding interaction with the adjacent molecules, which caused the increase of the dark-state energy in the crystalline state. Moreover, the restriction of the rotational motion and the nonexistence of the π-π stacking interaction are beneficial to the enhancement of fluorescence upon aggregation. Finally, the ACQ-to-AIE transformation mechanisms of fluorescein derivatives have been discussed. This work provides deeper insight into the photophysical mechanism for the fluorescein derivatives Fl-Me with AIE feature and eventually is expected to help researchers to develop more fluorescein-based AIE materials with remarkable properties for various fields.

Theoretical Investigation on the "ON-OFF" Mechanism of a Fluorescent Probe for Thiophenols: Photoinduced Electron Transfer and Intramolecular Charge Transfer.

In this study, the sensing mechanism of (2E,4E)-5-(4-(dimethylamino)phenyl)-1-(2-(2,4dinitrophenoxy)phenyl)penta-2,4-dien-1-one (DAPH-DNP) towards thiophenols was investigated by density functional theory (DFT) and time-dependent DFT (TD-DFT). The DNP group plays an important role in charge transfer excitation. Due to the typical donor-excited photo-induced electron transfer (d-PET) process, DAPH-DNP has fluorescence quenching behavior. After the thiolysis reaction between DAPH-DNP and thiophenol, the hydroxyl group is released, and DAPH is generated with the reaction showing strong fluorescence. The fluorescence enhancement of DAPH is not caused by an excited-state intramolecular proton transfer (ESIPT) process. The potential energy curves (PECs) show that DAPH-keto is less stable than DAPH-enol. The frontier molecular orbitals (FMOs) of DAPH show that the excitation process is accompanied by intramolecular charger transfer (ICT), and the corresponding character of DAPH was further confirmed by hole-electron and interfragment charge transfer (IFCT) analysis methods. Above all, the sensing mechanism of the turn-on type probe DAPH-DNP towards thiophenol is based on the PET mechanism.

Mechanistic Investigation on the Initial Thermal Decomposition of Energetic Materials FOX-7 and RDX in the Crystal and Gas Phase: An MM/DFT-Based ONIOM Calculation.

Interpreting the initial decomposition mechanism is important for evaluating the thermal stability of explosives. In this study, we theoretically investigated the initial thermal decomposition reactions for two typical energetic materials, FOX-7 and RDX, in both the gas phase and crystal phase. Single molecular decomposition pathways in the gas phase are calculated using the density functional theory (DFT) method, and the crystal phase reactions are simulated through the MM/DFT-based ONIOM method. The calculation results indicate that the crystal environment has a significant influence on the initial thermal decomposition mechanism of FOX-7 and RDX. The cage effect induced by the crystal environment greatly confines molecular mobility and diffusion, rendering the generated small molecules to react with the remaining fragment and yield new decomposition channels compared with the gas phase condition. The crystal packing structures and intermolecular interactions (hydrogen bonds/π-π stacking) significantly increase the reaction barriers of FOX-7 and RDX, leading to the crystal phase reactions being more difficult to occur than in the gas phase. Since the practical application of explosives is mostly in the crystal state, it is important to consider the environmental effects on the initial decomposition reactions. The same insight can also be relevant for other energetic materials.

Theoretical Investigations on the Sensing Mechanism of Phenanthroimidazole Fluorescent Probes for the Detection of Selenocysteine.

The level of selenocysteine (Sec) in the human body is closely related to a variety of pathophysiological states, so it is important to study its fluorescence sensing mechanism for designing efficient fluorescent probes. Herein, we used time-dependent density functional theory to investigate the fluorescence sensing mechanism of phenanthroimidazole derivates A4 and B4 for the detection of Sec, which are proposed to be designed based on excited state intramolecular proton transfer (ESIPT) and intramolecular charge transfer (ICT) mechanisms. The calculation results show that the fluorescence quenching mechanism of A4 and B4 is due to the photo-induced electron transfer (PET) process with the sulfonate group acts as the electron acceptor. Subsequently, A4 and B4 react with Sec, the sulfonate group is substituted by hydroxyl groups, PET is turned off, and significant fluorescence enhancement of the formed A3 and B3 is observed. The theoretical results suggest that the fluorescence enhancement mechanism of B3 is not based on ICT mechanism, and the charge transfer phenomenon was not observed by calculating the frontier molecular orbitals, and proved to be a local excitation mode. The reason for the fluorescence enhancement of A3 based on ESIPT is also explained by the calculated potential energy curves.

Highly Efficient and Ultralong Afterglow Emission with Anti-Thermal Quenching from CsCdCl3 : Mn Perovskite Single Crystals.

Triplet exciton-based long-lived phosphorescence is severely limited by the thermal quenching at high temperature. Herein, we propose a novel strategy based on the energy transfer from triplet self-trapped excitons to Mn2+ dopants in solution-processed perovskite CsCdCl3 . It is found the Mn2+ doped hexagonal phase CsCdCl3 could simultaneously exhibit high emission efficiency (81.5 %) and long afterglow duration time (150 s). Besides, the afterglow emission exhibits anti-thermal quenching from 300 to 400 K. In-depth charge-carrier dynamics studies and density functional theory (DFT) calculation provide unambiguous evidence that carrier detrapping from trap states (mainly induced by Cl vacancy) to localized emission centers ([MnCl6 ]4- ) is responsible for the afterglow emission with anti-thermal quenching. Enlightened by the present results, we demonstrate the application of the developed materials for optical storage and logic operation applications.

Dual fluorescence of 2-(2'-hydroxyphenyl) benzoxazole derivatives via the branched decays from the upper excited-state.

As a special fluorescence phenomenon, double fluorescence has been widely developed and applied in various fields. Nevertheless, most of the research on fluorescence emission channels focuses on the first excited state, while the research on how to control the fluorescence emission channel through the upper excited state is relatively under-explored. Here, we use the time-dependent density functional theory method and consider the 2-(2'-hydroxyphenyl) benzoxazole (HBO) derivative system as an example to study the effect of upper excited states on double fluorescence. According to the calculation results, a new mechanism for the dual fluorescence was proposed, which involved the different decay pathways from the upper excited-state, the internal conversion through vibrational relaxation, and conical intersection, respectively. This research has potential value and can help in determining how to control the fluorescence emission channel through the upper excited state.

A combined experimental and theoretical investigation of the excited-state dynamics of 2,4,6-trinitrotoluene (TNT) in DMSO solvent.

In the present contribution we carried out a TDDFT and femtosecond transient absorption study of the excited state dynamics of TNT in DMSO solvent. Vertical excitation and excited state relaxation were calculated at the SMD/M06-2X/TZVP level of theory. The electron absorption spectrum for the DMSO solvated TNT was calculated and compared with the experimental results. The results of the electronic excitation energies and the spin-orbital constants imply an intersystem crossing for the S1-T2 transition. The femtosecond time-resolved transient absorption measurements of the TNT in DMSO show the presence of two absorption signals around 650 nm and 540 nm, which are assigned to the population in the lowest singlet and triplet excited states, S1 and T1, respectively. The fast decay of the S1 state population is assigned to an efficient S1-T2 intersystem crossing, which soon internally converts to the T1 state. The slow decay of the T1 population is attributed to the nonradiative transition to the S0 state. The combined theoretical and experimental results present a mechanistic view of the photophysical dynamics of TNT in DMSO solution.

Controlling Photoluminescence and Photocatalysis Activities in Lead-Free Cs2 Ptx Sn1-x Cl6 Perovskites via Ion Substitution.

Lead-free halide perovskites have triggered interest in the field of optoelectronics and photocatalysis because of their low toxicity, and tunable optical and charge-carrier properties. From an application point of view, it is desirable to develop stable multifunctional lead-free halide perovskites. We have developed a series of Cs2 Ptx Sn1-x Cl6 perovskites (0≤x≤1) with high stability, which show switchable photoluminescence and photocatalytic functions by varying the amount of Pt4+ substitution. A Cs2 Ptx Sn1-x Cl6 solid solution with a dominant proportion of Pt4+ shows broadband photoluminescence with a lifetime on the microsecond timescale. A Cs2 Ptx Sn1-x Cl6 solid solution with a small amount of Pt4+ substitution exhibits photocatalytic hydrogen evolution activity. An optical spectroscopy study reveals that the switch between photoluminescence and photocatalysis functions is controlled by sub-band gap states. Our finding provides a new way to develop lead-free multifunctional halide perovskites with high stability.

Spin-Controlled Charge-Recombination Pathways across the Inorganic/Organic Interface.

Charge transfer and recombination across the inorganic/organic interface in nanocrystal or quantum dot (QD)-molecule hybrid materials have been extensively studied. Principles of controlling charge transfer and recombination via energetics and electronic coupling have been established. However, the use of electron spin to control transfer and recombination pathways in such systems remains relatively underexplored. Here we use CdS QD-alizarin (AZ) as a model system to demonstrate this principle. Using time-resolved spectroscopy, we found that the charge-separated states (QD--AZ+) created by selectively exciting AZ molecules mostly recombined to regenerate ground-state complexes, whereas apparently the "same" charge separated states created by exciting QDs recombined to produce AZ molecular triplet states. Such a difference can be traced to the distinct spin configurations between excited QDs (QD*, with an ill-defined spin) and AZ (1AZ*, spin singlet) and the asymmetric electron and hole spin-flip rates in II-VI group QDs. The transferability of such a principle was confirmed by similar observations obtained for CdS QD-tetracene complexes. Opening an avenue for controlling charge transfer and recombination pathways via electron spin is potentially important for applications such as artificial photosynthesis.

Quantifying the Fast Dynamics of HClO in Living Cells by a Fluorescence Probe Capable of Responding to Oxidation and Reduction Events within the Time Scale of Milliseconds.

The biological roles of reactive oxygen species (ROS) depend highly on their dynamics. However, it has been challenging for measuring the dynamics of ROS in cells. In this study, we address a core challenge in developing fluorescence probes for monitoring ROS dynamics by designing a redox couple that can respond rapidly to both oxidation and reduction events. We show that such molecules can be designed by taking advantage of the steric effects of electron-donating groups at the ortho position relative to the selenium center. We demonstrate this design in a new fluorescence probe named Fl-Se. Results reveal that Fl-Se and its oxidized product Fl-SeO rapidly respond to HClO, an important member of the ROS family, and glutathione (GSH), with t1/2 = 2.7 ms at [HClO] = 1 µM; t1/2 = 61 ms at [GSH] = 1 mM. When applied in cells, Fl-Se satisfactorily tracks the dynamics of intracellular HClO in H2O2-stimulated HL-60 cells, as well as the different dynamic behaviors of HClO fluctuations involved in the phorbol 12-myristate-13-acetate-activated immune response of RAW264.7 cells and the 3-deazaneplanocin A-induced apoptosis of HL 60 cells.

Competition between tubular, planar and cage geometries: a complete picture of structural evolution of Bn (n = 31-50) clusters.

Stimulated by the early theoretical prediction of B80 fullerene and the experimental finding of the B40 cage, the structures of medium-sized boron clusters have attracted intensive research interest during the last decade, but a complete picture of their size-dependent structural evolution remains a puzzle. Using a genetic algorithm combined with density-functional theory calculations, we have performed a systematic global search for the low-lying structures of neutral Bn clusters with n = 31-50. Diverse structural patterns, including tubular, quasi-planar, cage, core-shell, and bilayer, are demonstrated for the ground-state Bn clusters; for certain cluster sizes, unprecedented geometries are predicted for the first time. Their stabilities at finite temperatures are evaluated, and the competition mechanism between various patterns is elucidated. Chemical bonding analysis reveals that the availability of localized σ bonds and delocalized π bonds in the Bn clusters play a key role in their structural stability. Our results provide important insights into the bonding pattern and growth behavior of medium-sized boron clusters, which lay the foundation for experimental design and synthesis of boron nanostructures.

Sensing Mechanism of a Fluorescent Probe for Cysteine: Photoinduced Electron Transfer and Invalidity of Excited-State Intramolecular Proton Transfer.

The abnormal level of cysteine (Cys) in the human body will cause a series of diseases, and the study of the sensing mechanism is of great significance for the design of efficient fluorescent probes. Here, we used time-dependent density functional theory to study the sensing mechanism of a newly synthesized imidazo [1,5-α] pyridine-based fluorescent probe (MZC-AC) for the detection of Cys, which is proposed to be designed based on excited-state intramolecular proton transfer (ESIPT). We first show that the fluorescence quenching mechanism of MZC-AC is due to a nonclassical photoinduced electron transfer (PET) process in which the curve crossing between local excited and charge-transfer states is observed and the acrylate group acts as an electron acceptor. When the acrylate group is replaced by the hydroxyl group due to the reaction between MZC-AC and Cys, the PET is off and a significant fluorescence enhancement of the formed MZC is observed. Our theoretical results indicate that the fluorescence enhancement mechanism of MZC is not based on the ESIPT. The calculated potential energy curve along the proton transfer pathway shows that the electronic energy of MZC-keto is larger than that of MZC-enol. Moreover, the computed emission energy of MZC-enol is closer to the experimental data than that of MZC-keto. The experimentally observed large Stokes shift was ascribed to the intramolecular charge transfer character of the first excited state of MZC. Our theoretical results can explain well the fluorescence behavior of MZC-AC and MZC and invalidate the experimentally proposed ESIPT mechanism of MZC.

Thermochemistry and Initial Decomposition Pathways of Triazole Energetic Materials.

A thorough investigation of the initial decomposition pathways of triazoles and their nitro-substituted derivatives has been conducted using the MP2 method for optimization and DLPNO-CCSD(T) method for energy. Different initial thermolysis mechanisms are proposed for 1,2,4-triazole and 1,2,3-triazole, the two kinds of triazoles. The higher energy barrier of the primary decomposition path of 1,2,4-triazole (H-transfer path, ∼52 kcal/mol) compared with that of 1,2,3-triazole (ring-open path, ∼45 kcal/mol) shows that 1,2,4-triazole is more stable, consistent with experimental observations. For nitro-substituted triazoles, more dissociation channels associated with the nitro group have been obtained and found to be competitive with the primary decomposition paths of the triazole skeleton in some cases. Besides, the effect of the nitro group on the decomposition pattern of the triazole skeleton has been explored, and it has been found that the electron-withdrawing nitro group has an opposite effect on the primary dissociation channels of 1,2,4-triazole derivatives and 1,2,3-triazole derivatives.

Unraveling the Detailed Mechanism of Excited-State Proton Transfer.

As one of the most fundamental processes, excited-state proton transfer (ESPT) plays a major role in both chemical and biological systems. In the past several decades, experimental and theoretical studies on ESPT systems have attracted considerable attention because of their tremendous potential in fluorescent probes, biological imaging, white-light-emitting materials, and organic optoelectronic materials. ESPT is related to fluorescence properties and usually occurs on an ultrafast time scale at or below 100 fs. Consequently, steady-state and femtosecond time-resolved absorption, fluorescence, and vibrational spectra have been used to explore the mechanism of ESPT. However, based on previous experimental studies, direct information, such as transition state geometries, energy barrier, and potential energy surface (PES) of the ESPT reaction, is difficult to obtain. These data are important for unravelling the detailed mechanism of ESPT reaction and can be obtained from state-of-the-art ab initio excited-state calculations. In recent years, an increasing number of experimental and theoretical studies on the detailed mechanism of ESPT systems have led to tremendous progress. This Account presents the recent advances in theoretical studies, mainly those from our group. We focus on the cases where the theoretical studies are of great importance and indispensable, such as resolving the debate on the stepwise and concerted mechanism of excited-state double proton transfer (ESDPT), revealing the sensing mechanism of ESPT chemosensors, illustrating the effect of intermolecular hydrogen bonding on the excited-state intramolecular proton transfer (ESIPT) reaction, investigating the fluorescence quenching mechanism of ESPT systems by twisting process, and determining the size of the solute·(solvent) n cluster for the solvent-assisted ESPT reaction. Through calculation of vertical excitation energies, optimization of excited-state geometries, and construction of PES of the ESPT reactions, we provide modifications to experimentally proposed mechanisms or completely new mechanism. Our proposed new and inspirational mechanisms based on theoretical studies can successfully explain the previous experimental results; some of the mechanisms have been further confirmed by experimental studies and provided guidance for researchers to design new ESPT chemosensors. Determination of the energy barrier from an accurate PES is the key to explore the ESPT mechanism with theoretical methods. This approach becomes complicated when the charge transfer state is involved for time-dependent density functional theory (TDDFT) method and optimally tuned range-separated TDDFT provides an alternative way. To unveil the driving force of ESPT reaction, the excited-state molecular dynamics combined with the intrinsic reaction coordinate calculations can be employed. These advanced approaches should be used for further studies on ESPT systems.

New insights into the sensing mechanism of a phosphonate pyrene chemosensor for TNT.

As security needs have increased, mechanism investigation has become of high importance in the development of new sensitive and selective chemosensors for chemical explosives. This study details a theoretical investigation of the sensing mechanism of a new phosphonate pyrene chemosensor for trinitrotoluene (TNT), suggesting a different interaction mode between the probe and TNT from the one previously reported. The invalidity of the mechanism of binding TNT through intermolecular hydrogen bonds was proved using the Gibbs free energy profile and 1H NMR analysis. Frontier molecular orbitals (FMOs) analysis was used to show that photo-induced electron transfer (PET) is the underlying mechanism behind the luminescence quenching of the probe upon exposure to TNT, the rationality of which was further confirmed by the recording of a high charge transfer rate. We also found the existence of an energy level crossing between the local excited (LE) state and charge transfer (CT) state of a complex of the probe and TNT, which was confirmed using energy profile calculations along the linearly interpolated internal coordinate (LIIC) pathway.