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 (kic 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.

A wide range of gold-catalyzed reactions has continued to increase based on a dual activation mechanism. Herein, the diaurate-catalyzed synthesis mechanism of benzofulvenes through C(sp3)-H activation is thoroughly investigated by density functional theory (DFT). A few scenarios are highlighted, including the mode of catalyst transfer, the catalysis mechanism contrast between the Au center and two centers, and the manner of sigma-gold coordinated diyne formation. Three mechanistic pathways were computed: (a) a dual-catalysis pathway of precatalyst (pathway a), (b) a single-catalysis pathway (pathway b), and (c) a dual-catalysis pathway including 9,8-H transfer (pathway c). As for the reasonable pathway a, NTf2 - abstracts a proton from the pi-gold complex, generating a sigma-coordinated monogold complex. Subsequently, another catalyst coordinates, forming a sigma,pi-digold complex, which undergoes two consecutive cyclization steps to give non-gem-diaurated species. The reaction subsequently can proceed via three possible routes: (a 1) undergo pi-system slippage to yield gem-c, which then undergoes gold transfer and protonation with a substrate to afford benzofulvenes; (a 2) intermolecular protodeauration to generate sigma-monoaurated species, followed by protonation with HNTf2; and (a 3) protonation by HNTf2 occurs to generate pi-monoaurated species, which undergoes intermolecular protodeauration to form benzofulvenes.

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.

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 (kr) of TTB compared to that of TTB-CN. Furthermore, the presence of a fluorine atom in TTB enhances the intersystem crossing rate (kisc) 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 (FA), 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 FA detection. These probes are based on the principles of photoinduced electron transfer (PET) and twisted intramolecular charge transfer (TICT). In this article, 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 (TVCF) formalism 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 nonradiative 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 FA, can be attributed to the more rapid radiative transitions and relatively slower nonradiative 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 TPA detection in organisms. The reaction mechanism of Na-FA and FA 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 kr 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 kic 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 kisc 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.

Thermally activated delayed fluorescence (TADF) in compact electron donor-acceptor dyads has attracted great attention due to their potential application in organic light-emitting diodes. However, the lack of understanding of the microscopic mechanisms of this phenomenon hinders the design strategies for effective TADF materials. In this work, we systematically compared the TADF mechanism of three compact dyads with those of electron donor phenothiazine (PTZ) and acceptor anthraquinone (AQ) directly connected by a single C-N bond (AQ-PTZ, AQ-PTZ-O, and AQ-PTZ-O2) by means of quantum chemical calculations in conjunction with electron paramagnetic resonance (EPR) spectroscopy. It turns out that three targeted molecules for TADF are identified depending on the relative energy positions of the charge-transfer excited states, 1CT/3CT, and the local triplet state, 3LE states. In most TADF-active molecules, AQ-PTZ-O and AQ-PTZ-O2, the structure deformation of excited states is suppressed by oxidation of the PTZ unit, leading to a small relaxation energy and a reverse intersystem crossing (RISC) energy barrier, as well as 3LE being on-resonance with the CT states, thus resulting in high efficiency RISC. Analyses of the electron paramagnetic resonance (EPR) parameters have confirmed that the electron spin polarized (ESP) patterns of T1(1LE) for AQ-PTZ-O and AQ-PTZ-O2 are AEAEAE (A, absorption; E, emission) with a preferential population of Tx and Tz, which is characteristic of ISC mediated by SOC interactions. Namely, the primary population mechanism of the singlet excited state is spin-orbit charge-transfer RISC due to the presence of a perpendicular pi system. Their D values are expected to be positive, and display a more "disk-like" spin density distribution with an oblate shape; the calculated RISC rates also support these views. These results provide new gateways for designing effective TADF materials and studying TADF mechanisms. Thermally activated delayed fluorescence (TADF) in compact electron donor-acceptor dyads has attracted great attention due to their potential application in organic light-emitting diodes.

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 (kiosk) and reverse intersystem crossing rate (krisc) 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 krisc (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.

We have designed and synthesized a novel fluorescent probe BMH for detection of hypochlorous acid (HClO), which can increase dramatically the fluorescence intensity and had ultrafast response, a low detection limit and a wide pH range of application. In this paper, we further studied its fluorescence quantum yield and photoluminescence mechanism theoretically. The calculated results indicated the first excited states of BMH and BM (it was the oxidized product by HClO) were bright states with large oscillator strengths, however, due to more larger reorganization energy of BMH, the predicted internal conversion rate kIC of BMH was four orders of magnitude larger than that of BM; moreover, owing to the effect of heavy atom from sulfur atom in BMH, the predicted intersystem crossing rate kisc of BMH was five orders of magnitude larger than that of BM; meanwhile there was no significant difference found between both the predicted radiative rates kr, thus the calculated fluorescence quantum yield of BMH was nearly zero and that of BM was more than 90%, the data showed the BMH had no fluorescence but its oxidated produce BM possessed strong fluorescence. In addition, the reaction mechanism of BMH transforming into BM has been investigated too, according to the potential energy profile, we found that the course of BMH converting into BM consisted of three elementary reactions. The research results revealed the solvent effect can decreased the activation energy, which was more favorable for these elementary reactions.

A highly selective probe for copper(II) detection based on the dansyl group was theoretically studied by means of (time-dependent) density functional theory. The calculated results indicated that the oscillator strength of the fluorescent process for the probe molecule is considerably large, but the counterpart of its copper(II) complex is nearly zero; therefore, the predicted radiative rate kr of the probe is several orders of magnitude larger than that of its complex; however, the predicted internal conversion rate kic of both the probe and its complex is of the same order of magnitude. In addition, the simulated intersystem crossing rate kisc of the complex is much greater than that of the probe due to the effect of heavy atom from the copper atom in the complex. Based on the above information, the calculated fluorescence quantum yield of the probe is 0.16% and that of the complex becomes 10-6%, which implies that the first excited state of the probe is bright state and that of the complex is dark state. For the complex, the hole-electron pair analysis indicates that the process of S0 → S1 belongs to metal-to-ligand charge transfer; its density-of-state diagram visually illustrates that the highest occupied molecular orbital (HOMO) contains the ingredient of the s orbital from the copper atom, which decreases the frontier orbital energy level and the overlap integral of HOMO and LUMO.

Theoretical calculation not only is a powerful tool to deeply explore photophysical processes of the emitters but also provides a theoretical basis for material renewal and design strategy in the future. In this work, the interconversion and decay rates of the thermally activated delayed fluorescence (TADF) process of the rigid Ag(dbp)(P2-nCB) complex are quantitatively calculated by employing the optimally tuned range-separated hybrid functional (ω*B97X-D3) method combined with the path integral approach to dynamics considering the Herzberg-Teller and the Duschinsky rotation effects within a multimode harmonic oscillator model. The calculated results show that the small energy splitting ΔE(S1-T1) = 742 cm-1 (experimental value of 650 cm-1) of the lowest singlet S1 and triplet T1 state and proper vibrational spin-orbit coupling interactions facilitate the reverse intersystem crossing (RISC) processes from the T1 to S1 states. The k RISC rate is estimated to be 1.72 × 108 s-1 that is far more than the intersystem crossing rate k ISC of 7.28 × 107 s-1, which will greatly accelerate the RISC process. In addition, the multiple coupling routes of zero-field splitting (ZFS) interaction can provide energetically nearby lying states, to speed up the RISC pathway, and restrict the phosphorescence decay rate. A smaller ZFS D-tensor of 0.143 cm-1, E/D ≈ 0.094 ≪ 1/3, and Δg > 0 are obtained, indicating that the excited singlet states are hardly mixed into the T1 state; thus, a lower phosphorescence decay rate (k p = 9.29 × 101 s-1) is expected to occur, and the T1 state has a long lifetime, which is helpful for the occurrence of the RISC process. These works are in excellent agreement with the experimental observation and are useful for improving and designing efficient TADF materials.

Hypochlorous acid (HOCl) is widely used in daily production and life. It is also a kind of endogenously produced reactive oxygen species (ROS) in the human immune system, plays a crucial role in many pathophysiological processes. This work designed and synthesized a novel based on benzocoumarin fluorescent probe BL for specific detection HOCl. BL has brilliant selectivity, high sensitivity (5.64 nM), fast response (60 s), moderate water solubility. The intramolecular charge transfer (ICT) sensing mechanism of BL has been verified by fluorescence, UV, MS, and density functional theory (DFT) calculations. BL can make into a solid-state visual sensor to detect HOCl conveniently. BL was also applied to detect HClO spiked in tap water, 84 disinfectants, lake water, and satisfying recovery rates. Finally, BL was low toxic and used to track the variations of endogenous/exogenous HClO in living cells successfully. Totally, BL provides a powerful and reliable monitoring tool to reveal the biological functions of HOCl and ensure safe use.

DFT/TD-DFT, NBO and AIM methods were applied to explore the synthetic homo-metallophilic Pt center dot center dot center dot Pt (d(8)center dot center dot center dot d(8)) complex (self-assembled by lPt(C boolean AND NI boolean AND N-pyr)(C NPh)](+), HC boolean AND N boolean AND N-pyr = 2-phenyl-6-(1H-pyrazol-3-yl)-pyridine)]) recently reported with good photophysical properties. The calculated geometries and the spectroscopies of the complexes are consistent with the experiment. The strong phosphorescence of experimental observation for Pt dimer was evidenced by its bigger order of mu(S1)/Delta ES1-T1 values (mu(S1): S-0 -> S-1 transition dipole, Delta ES1-T1: splitting energy between the lowest-lying singlet S-1 and the triplet excited state T-1 states). The phosphorescence spectra are predicted to be blue-shifted under polar solvent water comparing those in gas. The calculated maximal absorption is predominantly characteristic with MLCT/ILCT/LLCT whereas the photophysical spectrum was found to be responsible for the 3MLCT characters in the Pt-dimer. In addition, on the basis of complex Ptmonomer and Pt-dimer, Pd-monomer, Pd-dimer and Pt,Pd-dimer were constructed to investigate the modulation of Pd-substitued on the structure and spectroscopic properties of monomer and dimer [M(C boolean AND N boolean AND N-pyr) (C NPh)](+) complex.

Stimulation-responsive luminescent materials have attracted intense attention due to their excellent optical properties in the anti-counterfeiting application. At present, most the anti-counterfeiting materials are based on single luminescence and fixed excitation patterns, resulting in a poor anti-counterfeiting effect. Therefore, developing multimodal anti-counterfeiting materials that change their luminous color under different wavelength stimuli has become a significant challenge. In this work, we reported a multimodal luminescent La4Ga2O9: Bi3+, Er3+ material, which could emit white, blue-green, baby blue and orange-yellow light at the excitation wavelength of 250nm~430nm. Moreover, it also showed green upconversion (UC) luminescence when irradiated with near-infrared (NIR, 980nm and 808nm) lasers. Notably, the material exhibited good humidity resistance and stability. Based on these integrated features, we designed an anticounterfeiting device. Results suggested that the anticounterfeiting device could quickly realize multimodal anti-counterfeiting using common light source (NIR (808nm or 980nm) laser and UV lamp). These combined characteristics will be difficulty to forge and show high security in anticounterfeiting applications.

Hypochlorous acid (HOCl) is widely used in daily production and life because of its green and strongly oxidizing properties. Additionally, as a vital reactive oxygen species (ROS), it is an innate immune system weapon and performs a critical function in many pathophysiology processes. In this paper, a novel water-soluble fluorescent probe, BMH, with excellent performance is designed and synthesized by simple condensation of benzocoumarin and 2-mercaptoethanol. BMH has specific selectivity, excellent sensitivity, ultra-fast response (<3 s), and a wide pH detection range. The fluorescence intensity of BMH has an excellent linear correlation with the concentration of HOCl in the scope of 0-10 μM, and the calculated detection limit (DL) is 2.45 nM. The intramolecular charge transfer (ICT) sensing mechanism of BL has been verified by fluorescence, UV, and MS studies as well as density functional theory (DFT) calculations. Furthermore, BMH can be incorporated into a solid-state visual sensor to detect HOCl conveniently. BMH was applied to detect HOCl-spiked actual water samples and achieved satisfying recovery rates. Also, the low-toxicity BMH can be successfully used to track changes in endogenous/exogenous HOCl in living cells. In short, BL provides a robust and reliable monitoring tool to reveal the biological functions of HOCl and ensure its safe use.

Stimulation-responsive luminescent materials have attractd intense attention due to their excellent optical properties in the anticounterfeiting application. At present, most the anticounterfeiting materials are based on single luminescence and fixed excitation patterns, resulting in a poor anticounterfeiting effect. Therefore, developing multimodal anticounterfeiting materials that change their luminous color under different wavelength stimuli has become a significant challenge. In this work, we reported a multimodal luminescent La4GeO8: Bi3+, Er3+ phosphor, which could emit white, blue-green, baby blue and orange-yellow light at the excitation wavelength of 250-430 nm. Moreover, it also showed green upconversion (UC) luminescence when irradiated with near-infrared (NIR, 980 nm and 808 nm) lasers. Notably, the material exhibited good humidity resistance and stability. Based on these integrated features, we designed an anticounterfeiting device. The results suggested that the anticounterfeiting device could quickly realize multimodal anticounterfeiting using common light source {NIR (808 nm or 980 nm) laser and ultraviolet (UV) lamp}. These combined characteristics will be difficulty to forge and show high security in anticounterfeiting applications.

In this paper, we employed first-principles methods and the QM/MM technique to study the thermally activated delayed fluorescence (TADF) phenomenon of a near-infrared molecule (PIPAQ) in vacuum, solution, and the aggregation state. Our calculated results show that (1) the cluster can decrease the energy gap between the first singlet excited state (S1) and the first triplet state (T1) compared with the monomer, furthermore, the T1 state and S1 state in the cluster are energetically closer to each other, which implies that the energy gap is smaller in comparison with that in solution and can promote the intersystem crossing (ISC) process due to the surrounding effect; (2) the optimally tuned range-separated functional is applicable to simulation of excited states and the outcomes are in good agreement with experimental values; (3) the reorganization energies associated with ISC and the reverse intersystem crossing (RISC) processes between the S1 and T1 states are sensitive to the calculated methods and the environments, and thus the following calculated ISC and RISC rates vary dramatically according to different reorganization energies; (4) all radiative and nonradiative rates are insensitive to temperature, but sensitive to environments, all the radiative rates increase in the cluster while the nonradiative rates decrease, which enhances the fluorescence quantum efficiency and agrees with the observed value. The above results demonstrate that the surrounding effects are very important for modulating the photophysical properties of the PIPAQ compound. Finally, this studied conclusion can give a helpful insight into the TADF mechanism for the title compounds, by which novel TADF materials with excellent performance could be rationally designed.

The displaced and distorted harmonic oscillator model, which has been proven to be appropriate in calculating vibronic spectra, is employed to treat the emission spectrum of title molecules in combination with a thermal vibration correlation function. The calculated results indicate that the main peak of the emission spectrum is visibly impacted by the normal modes with lower frequencies and that the shoulder peak is originated from the middle-frequency modes. On the level of time-dependent density functional theory (TDDFT), the calculated fluorescence lifetimes of TTM-3NCz and TTM-3PCz are 22.1 and 26.0 ns, respectively, which happen to coincide with the observed values of TTM-3NCz (17.2 ns) and TTM-3PCz (21.2 ns). The above data indicate that both the calculated radiative decay rates are reasonable at room temperature. Furthermore, we investigate the influence of the Duschinsky effect on the fluorescence quantum efficiency (FQE). When it is considered, the predicted FQE of the TTM-3NCz molecule is only 0.11%, and the observed value (49% in toluene) deviates significantly. If we ignore the Duschinsky effect, the FQE of TTM-3NCz increases dramatically to 41.8%. For the TTM-3PCz molecule (the FQE is 46% in toluene), the calculated FQE is 0.042% with the Duschinsky effect and increases to 45.2% without the Duschinsky effect. This phenomenon might be related to external factors and the nature of the TDDFT only considering a single configuration. In addition, the fluorescent properties of the fluorinated TTM-3NCz molecules are studied predictably. The obtained results show that the perfluorinated TTM-3NCz shows better luminous performance due to larger oscillator strength. Finally, the dimers, which are composed of both single title molecules, are explored theoretically to determine how they impact the fluorescent property; however, the effect can be nearly eliminated because of the small binding energies.

The single molecular configuration of 3-furoic acid was optimized using the density functional theory B3LYP/6-311G+ (d,p) and the second-order perturbation theory MP2/6-311+G (d, p), and both the stable geometries were obtained, the barrier of the isomerization reaction, which corresponds to the configuration I turning into the configuration II, is 32. 10 kJ.mol(-1), which implies the isomerization reaction is very difficult to occur. The percentage of the configuration I with low energy is much more than that of the configuration II with high energy based on Boltzmann distribution law, which shows that the configuration I is stabler at room temperature. The vibration frequency of the monomer was calculated based on the stable structures at the same level in anharmonic force field, the potential energy distribution(PED) of each vibration frequency was calculated and the normal modes were analyzed and assigned, and the absorption peaks between 2 000 similar to 2 500 cm(-1) can be explained using double frequency and combined frequency. It was found that the calculated IR spectrum of the monomer matched up with the experimental gaseous IR spectrum. As to the dimer, the M06 density functional was employed to simulate the nature for including the corrective term of weak interaction, the calculated IR spectrum of the dimer in anharmonic force field was familiar to the experimental IR spectrum of the solid-state, based on the theoretical computation, the weak peaks appearing on 2 000 similar to 3 000 cm(-1) wavenumbers correspond to all kinds of overtone vibrations, the infrared transition between the vibrational ground state, of which the quantum number is 0, and the second vibrational excited state, of which the quantum number is 2, is too weak and can be ignored, and these overtone peaks are mainly from the sum of the fundamental frequencies, due to the dimers binding together with hydrogen bonds instead of chemical bonds, the rigidity of dimers is lower, and the anharmonicity of dimers increases, the intensity of the related overtone peaks also increases with the anharmonicity, these peaks in the dimer become very evident compared with those in the monomer, which agree with the experimental spectrum, however, because of a variety of dimers and polymers in the actual solid state, the intensity of the absorption peaks of the hydroxyl is reduced and the peak width of that is widened, in addition to the lack of the suitable parameters to calculate weak interaction, the universal force field and reasonable dispersion correcton factors in quantum chemistry makes the calculated spectra have certain error compared with the experiment ones, further more, the natural bond orbital (NBO) analysis was performed to reveal the origin of interaction, and it was found that the second order stabilization energy from the oxygen atom in the carboxyl group as the donor and the hydroxyl as the acceptor is 121. 4 kJ.mol(-1), the binding energy between the dimer is 65. 27 kJ.mol(-1), the amount of transferred charge from the donor orbital to the acceptor orbital is 0. 067 electron. The result showed that the intermolecular interaction of 3-furoic acid mainly originated from the intermolecular hydrogen bond. The Gibbs free energy change Delta G of the dimer under different temperatures were computed, the dimer will become unstable at 500 K for the Delta G of the dimer being positive value, the hydrogen bond is destroyed, and all the monomers will get together with molecular interaction.