Huixue Li

DFT calculations reveal the water-assisted mechanism of dual gold-catalyzed indene formation, highlighting water’s dual role as a hydroxyl source and proton shuttle and the key steps leading to CO extrusion.

Phosgene (COCl₂) is a highly toxic industrial gas, and exploring the photophysical sensing mechanism of fluorescent probes is critical for rational probe optimization. Herein, time-dependent density functional theory (TD-DFT) and thermal vibration correlation function (TVCF) calculations were performed to clarify the excited-state decay mechanism of the 8-EDAB probe. The free 8-EDAB exhibits extremely weak fluorescence (Φ = 0.0045%), while its phosgene cyclized product displays significantly enhanced emission (Φ = 12.44%). The fluorescence turn-on behavior is attributed to cyclization-induced intramolecular charge transfer (ICT) suppression, which greatly reduces the internal conversion rate (k_ic from 10¹¹ to 10⁹ s^-1) and switches the dominant excited-state deactivation pathway from nonradiative decay to radiative fluorescence. Both molecules exhibit two-photon absorption capability, revealing potential bioimaging applicability. Furthermore, we rationally designed two hybrid local charge-transfer (HLCT) derivatives, 8-EDAB-S-3NH₂ and 8-EDAB-5CH₃, whose cyclized products achieve ultrahigh fluorescence quantum yields of 97.28 and 84.39%, respectively. The improved emission originates from dramatically suppressed internal conversion caused by molecular rigidification, rather than reverse intersystem crossing (RISC) triplet harvesting. Unlike the original experimental work, this study provides the first quantitative TVCF-based mode-resolved analysis of internal conversion suppression and demonstrates a predictive HLCT-based design strategy for high-performance phosgene probes.

This study established a multiscale theoretical framework integrating the polarizable continuum model (PCM), time-dependent density functional theory (TD-DFT), and thermal vibration correlation function (TVCF) to explore the photophysical properties and fluorescence quantum yield of the 4F-2CN fluorescent probe. Theoretical results show that 4F-2CN emits fluorescence in the ultraviolet region with a quantum yield ≤ 0.5%, resulting in undetectable visible emission. By contrast, its cysteine reaction product (4F-2CN-Cys) exhibits visible fluorescence with high quantum yield; notably, the value calculated via the CAM-B3LYP method matches experimental data, verifying 4F-2CN’s validity as a cysteine probe. 4F-2CN-Cys also displays a markedly enhanced near-infrared (NIR) two-photon absorption (TPA) cross-section, enabling deep-tissue imaging applications. Potential energy surface analysis confirms ion-mediated pathway B as the dominant reaction route due to its lower activation energy. Molecular design simulations suggest substituting fluorine in 4F-2CN with chlorine or bromine can improve single-photon and two-photon absorption/emission properties, offering practical strategies for developing next-generation NIR two-photon fluorescent probes. This work provides critical theoretical insights into probe-cysteine interaction mechanisms and molecular design optimization.

Cyanide (CN^-), a highly toxic substance, is prevalent across industrial, agricultural, and natural environments, posing a grave threat to human health and ecosystems. Numerous fluorescent probes for cyanide detection have been developed based on mechanisms such as photoinduced electron transfer (PET) and intramolecular charge transfer (ICT). In this study, a theoretical approach was employed to investigate the sensing mechanism, photophysical properties, and reaction pathways of the TTB fluorescent probe in tetrahydrofuran (THF) solvent. This approach integrates the polarizable continuum model (PCM), time-dependent density functional theory (TD-DFT), and the thermal vibration correlation function formalism (TVCF) to provide a comprehensive understanding of the probe's properties and behaviors. The photophysical and chemical properties of the fluorescent probe TTB and its cyanide adduct, TTB-CN, were systematically investigated. The results indicate that the TTB probe itself exhibits negligible fluorescence, whereas the product formed upon binding with cyanide demonstrates significant fluorescence emission. This difference is attributed to the substantially lower predicted radiative decay rate (k_r) of TTB compared to that of TTB-CN. Furthermore, the presence of a fluorine atom in TTB enhances the intersystem crossing rate (k_isc) by a factor of 7 relative to TTB-CN. Consequently, the calculated fluorescence quantum yield of TTB is only 0.042%, while that of TTB-CN exceeds 18.14%. These findings provide a scientific basis for the application of TTB as a fluorescent probe. Investigations into the reaction mechanism demonstrate that this reaction proceeds as a nucleophilic reaction featuring a relatively low energy barrier. Additionally, our calculations reveal that both TTB and TTB-CN exhibit two-photon absorption properties, suggesting their potential for two-photon-based detection in biological systems.

Formaldehyde, a significant signal molecule in biological systems, is considered as many physiological processes and pathological diseases. Up to now, a number of fluorescent probes, crafted from naphthalene amide-hydrazine scaffolds, have been designed and synthesized for the purpose of formaldehyde detection. These probes are based on the principles of photoinduced electron transfer (PET) and twisted intramolecular charge transfer (TICT). In this paper, we employed a theoretical method to undertake a comparative analysis of the sensing mechanisms, photophysical characteristics, and reaction mechanism of Na-FA (6-hydrazineyl-2-propyl-1H-benzo[de]isoquinoline-1,3(2H)-dione) probe in aqueous environments. This method integrates the polarizable continuum model (PCM), time-dependent density functional theory (TD-DFT), and the thermal vibration correlation function formalism (TVCF) to provide a comprehensive understanding of the probe’s properties and behaviors. Our results indicated that the weak emission of Na-FA owes to the TICT and non-radiative dissipation, conversely, PET has little effect on it. In contrast, the bright emission, exhibited by the reaction product NZ (6-(2-methylenehydrazineyl)-2-propyl-1H-benzo[de]isoquinoline-1,3(2H)-dione) of probe molecule Na-FA and formaldehyde, can be attributed to the more rapid radiative transitions and relatively slower non-radiative transitions, and there is no PET involved. In addition, we found NZ possesses a greater two-photon absorption (TPA) cross section in the near infrared region compared with that of Na-FA molecule, which determines its application in two-photon absorption detection in organisms. The reaction mechanism of Na-FA and formaldehyde producing NZ has been investigated as well, according to the potential energy profile, we discovered that path B corresponds to a lower activation energy with the aid of ion participation, therefore, path B is a more favorable reaction pathway. At last, we predicted the one-photon and two-photon properties of thiol-substituted naphthalimide, and the calculated results indicated that this compound has excellent potential as a two-photon fluorescent probe.

The photophysical and photochemical properties of the sulfonyl azide‐based fluorescent probe DNS–Az and its reduction product DNS by hydrogen sulfide (H₂S) have been investigated theoretically. The calculated results indicated the first excited states of DNS–Az was dark state (oscillator strength less than 0.03) and DNS was bright state (oscillator strength more than 0.1), which determined the predicted radiative rate k_r of DNS–Az was much smaller than that of DNS, meanwhile, due to more larger reorganization energy of DNS–Az, its predicted internal conversion rate k_ic was four times larger than that of DNS; moreover, owing to the effect of heavy atom from sulfur atom in DNS–Az, its predicted intersystem crossing rate k_isc was seven times larger than that of DNS, thus the calculated fluorescence quantum yield of DNS–Az was only 2.16% and that of DNS was more than 77.2%, the above factors is the basis for DNS–Az molecule to function as a fluorescent probe. Regarding both DNS‐Az and DNS molecules, their maximum Huang‐Rhys factors, which are less than unity, signify the reliability of 0–0 transitions between their S₀ and S₁ electronic states. In addition, for DNS, our simulated emission peak of the 0–0 transition is 515 nm, a value that exhibits enhanced accuracy and coherence when compared to the experimental datum of 528 nm. The reaction mechanism of DNS‐Az generating DNS by H₂S has been investigated too, according to the potential energy profile, we found that the fluorescent probe firstly protonated, then this organic ion broke down into DNS with the aid of a proton.

Iodination has unlocked new potentials in organic photovoltaics (OPVs). A newly designed and synthesized iodinated non‐fullerene acceptor, BO‐4I, showcases exceptional excitation delocalization property with the exciton diffusion length increased to 80 nm. The enhanced electron delocalization property is attributed to the larger atomic radius and electron orbit of the iodine atom, which facilitates the formation of intra‐moiety excitations in the acceptor phase. This effectively circumvents the charge transfer state‐related recombination mechanisms, leading to a substantial reduction in non‐radiative energy loss (ΔE_nr). As a result, OPV cell based on PBDB‐TF : BO‐4I achieves an impressive efficiency of 18.9 % with a notable ΔE_nr of 0.189 eV, markedly surpassing their fluorinated counterparts. This contribution highlights the pivotal role of iodination in reducing energy loss, thereby affirming its potential as a key strategy in the development of advanced next‐generation OPV cells.

We conducted a theoretical investigation into how the molecular stacking effect impacts the photophysical properties in solid phases. Our findings indicated that in the aggregated state, the out-of-plane distorted vibration and imidazole ring stretching vibration of triimidazo-[1,3,5] triazinethe are significantly suppressed, which decreased the Huang-Rhys factor and the corresponding reorganization energy of the photophysical process, as a result, this restricted intramolecular motions and dissipation pathways of excess energy in the excited state, therefore, aggregation induced enhancement emission (AIEE) was found for the title compound from dichloromethane solution to solid state. Analysis of the emission spectrum through discrete spectral lines revealed that the main peak was affected by the vibrational modes with lower frequencies, while the middle-frequency modes influenced the shoulder peak. Furthermore, the predicted intersystem crossing rate (k_iosk) and reverse intersystem crossing rate (k_risc) using Marcus theory confirmed that an electron can successfully shift from its S₁ state to the T₁ state, however, the reverse T₁ → S₁ process can not come into being due to very small k_risc (10^–6–10^–9 s^–1), therefore the phosphorescence can be observed. At last, we explored the influence of charge transfer process of the title compound, our theoretical data declared this process can be ignored due to its low transfer rate.