Ultrafast Photoisomerization of N-(2-Methoxybenzylidene)aniline: Nonadiabatic Surface-Hopping Study.

We investigated the ultrafast photoisomerization of N-(2-methoxybenzylidene)aniline in the gas phase excited into the second singlet (S2) state by nonadiabatic surface-hopping dynamics calculations. Two trans isomers (1E and 1E') were taken into consideration in our dynamics simulation. Three conical intersections (CIs) were characterized in the optimization. The CI between S2 and the first singlet (S1) states presents a nearly planar structure, while the other two CIs (CItwist-I and CItwist-II) between S1 and the ground (S0) states show nearly perpendicular geometries. After two trans isomers excited to the S2 state, the torsion of the C-N bond connected the phenyl group and the stretch of the central bridging bond make the molecule reach CIplanar, and the S2/S1 hopping occurs. During the S1-state dynamics, the molecule moves to a S1/S0 CI (CItwist-I or CItwist-II) by the rotation of the central bridging bond. The cis isomer is obtained through a barrierless pathway in the S0 state with the torsion of the three bridging bonds. There is a main channel and an alternative one for the photoisomerization process of both trans isomers. CItwist-I and CItwist-II act as S1/S0 decay funnels in the main isomerization channels of 1E and 1E' isomers, respectively, and the photochemical processes of 1E and 1E' lead to different cis isomers.

Programmable liquid crystal display based noise reduced dynamic synthetic coded aperture imaging camera (NoRDS-CAIC).

Besides traditional lens-based imaging techniques, coded aperture imaging (CAI) can also provide target images but without using any optical lenses, therefore it is another solution in imaging applications. Most CAI methods reconstruct target image only from a single-shot coded image using a fixed coding mask; however, the collected partial information inevitably deteriorates the reconstruction quality. Though multi-exposure CAI methods are designed, these existed algorithms can hardly improve reconstruction signal-to-noise ratio (SNR) and spatial resolution simultaneously; additionally, dynamic coding mask display still requires expensive devices and complicated systems. In order to reconstruct target image with both enhanced spatial resolution and SNR but using cost-effective devices and a simple system, we design a noise reduced dynamic synthetic coded aperture imaging camera (NoRDS-CAIC) in this paper. The NoRDS-CAIC only consists of a programmable liquid crystal display (LCD) and an image recorder, and both of them are integrated with a three-dimensional printed shell with the compact size of 19 cm × 15 cm × 16 cm and controlled by our designed software to automatically realize coding mask display, coded image recording and target image reconstruction. When using the NoRDS-CAIC, the optimized coding mask is first sent to the programmable LCD and displayed, then the corresponding coded image is automatically captured using the image recorder. Next, cycle the above procedures to capture enough coded images with previously known coding masks and measured point spread functions (PSFs), and the target image can be finally reconstructed using our designed NoRDS-CAIC decoding algorithm, which is shown with better noise suppression capability and higher reconstruction resolution compared to other classical CAI algorithms. According to the experimental verifications, the NoRDS-CAIC can reach the high resolution of 99.2 µm and the high SNR of 19.43 dB, proving that the designed NoRDS-CAIC can be potentially used for lensless imaging in practical applications.

Asymmetric localization induced by non-Hermitian perturbations with PT symmetry in photonic lattice.

We study both theoretically and numerically the asymmetric localization of lightwave in a three-layered photonic lattice with non-Hermitian perturbations. The results indicate that the gauge potential for photons can arise from the non-Hermitian perturbations, once the perturbations satisfy parity-time symmetry. Further study shows that the Peierls phase between adjacent waveguides has an important impact on the shapes of the band structures, which result in asymmetric localization of a lightwave in such a system when the wave number and Peierls phase satisfy k=ϕ=±π/2. This Letter provides a new way to control the light transmission and a feasible method to realize gauge potential for photons.

Ultrafast trans-cis photoisomerization of the neutral chromophore in green fluorescent proteins: Surface-hopping dynamics simulation.

Reversible photoswitching fluorescent protein can reversibly switch between on-state (fluorescent) and off-state (dark). Anionic cis and neutral trans chromophores are the on- and off-states in green fluorescent proteins (GFPs), respectively. We investigated the ultrafast trans-cis photoisomerization mechanisms of the neutral GFP chromophore upon excitation to the S1 state by means of surface-hopping dynamics simulations based on the Zhu-Nakamura theory. Two trans isomers, located in the S0 state, were taken into consideration in dynamics simulation. After these two trans isomers are excited to the S1 state, the molecule moves to a excited-state minimum by increasing the imidazolinone-bridge bond length and decreasing the phenol-bridge bond length. The twist of imidazolinone-bridge bond drives the molecule toward a conical intersection, and internal conversion occurs. Then, a cis or trans conformer will be obtained in the S0 state. The torsion around the imidazolinone-bridge bond plays a key role in the ultrafast photoisomerization of a neutral chromophore. The torsional motion around the phenol-bridge bond is restricted in the S1 state, while it may occur in the S0 state. The isomerization reaction of this molecule is predicted to be not sensitive to solvent viscosity, and time-dependent density functional theory (TDDFT) calculations indicate that the fast excited-state decay from the Franck-Condon region of the trans isomer to the excited-state minimum was almost independent of solvent polarity.

Nonadiabatic ab initio molecular dynamics study of photoisomerization in N-salicilydenemethylfurylamine (SMFA).

The photoisomerization mechanisms of N-salicilydenemethylfurylamine upon excitation to the first singlet state are investigated by means of surface-hopping dynamics simulations based on the Zhu-Nakamura theory. Due to different orientations of the methyl-furyl part with respect to the salicylaldimine part and different orientations of hydroxy group with respect to the benzene ring, various stable structures are obtained in the optimization. The enol isomer, S0-ENOL-5a, is the most stable conformer. An ultrafast excited-state intramolecular proton transfer is observed after photoexcitation of the most stable enol conformer and then the molecule reaches the excited-state minimum. After the internal conversion around a conical intersection, the system relaxes to either the cis-keto or trans-keto region in the ground state. The potential energy profiles of the ground and the first excited singlet state are also calculated. According to full-dimensional nonadiabaticdynamics simulations and potential energy profiles, the trans-keto and cis-keto photoproducts can be responsible for the photochromic effect of N-salicilydenemethylfurylamine.

Non-adiabatic dynamics of isolated green fluorescent protein chromophore anion.

On-the-fly ab initio molecular dynamics calculations have been performed to investigate the relaxation mechanism of green fluorescent protein chromophore anion under vacuum. The CASSCF surface hopping simulation method based on Zhu-Nakamura theory is applied to present the real-time conformational changes of the target molecule. The static calculations and dynamics simulation results suggest that not only the twisting motion around bridging bonds between imidazolinone and phenoxy groups but the strength mode of C=O and pyramidalization character of bridging atom are major factors on the ultrafast fluorescence quenching process of the isolated chromophore anion. The abovementioned factors bring the molecule to the vicinity of conical intersections on its potential energy surface and to finish the internal conversion process. A Hula-like twisting pattern is displayed during the relaxation process and the entire decay process disfavors a photoswitching pattern which corresponds to cis-trans photoisomerization.

Expression of Sox2 in cervical squamous cell carcinoma.

PURPOSE: Sox2, one of the genes that maintains self-renewal of embryonic stem cells and relates to the differentiation potential of these cells, is abnormaly expressed in various human tumors. We investigated the expression Sox2 in normal cervix and cervical squamous cell carcinoma (SCC), and we also assessed the prognostic significance of Sox2 expression in FIGO stage I-II cervical SCC. METHODS: Immunohistochemistry was performed to define the expression of Sox2 in 20 normal cervical tissue samples and 55 samples of cervical SCC. Correlations with clinicopathological characteristics were determined by chi-square test. The prognostic impact of Sox2 expression with regard to overall disease-free survival (DFS) was determined by the Kaplan-Meier method. RESULTS: The positive expression rate in cervical SCC was 74.5% (41/55), while in normal cervix it was 20.0% (4/20; p=0.000. In addition, the expression of Sox2 did not correlate with clinical factors (p>0.05). The overall DFS rates with negative and positive expressions of Sox2 were 35.7 and 29.3%, respectively (p=0.360). CONCLUSIONS: Our results show that Sox2 was overexpressed in FIGO stage I-II cervical SCC, indicating that overexpressed Sox2 may play an important role in the carcinogenesis of cervical SCC. Besides, we found that the expression of Sox2 had no relation to clinical factors and prognosis.

Wavelength-dependent photoisomerization of trans-4,4'-azopyridine: Nonadiabatic dynamics simulation.

The trans-cis photoisomerization processes of 4,4'-azopyridine upon S1 and S2 excitations have been investigated by nonadiabatic dynamics simulations based on multi-reference CASSCF calculations. 119 sampling trajectories were simulated starting from the trans form excited to the S1 (S2) state and the cis-isomer quantum yield is evaluated to be (3 ± 2)% ((18 ± 4)%), which is qualitatively in agreement with the recent experimental results in ethanol. We found that rotation around the central N-N bond accompanied by the N-N-C symmetrical bending vibrations is the main mechanism in photoisomerization of the target molecule excited to the S1 and S2 states. Upon S1 excitation, S1-S0 transition occurs earlier along the C-N-N-C torsional coordinate, leading to a low cis-isomer quantum yield. Upon S2 excitation, half of the simulated trajectories are trapped in a potential well on the S2 state, from which the twisted conical intersections are more easily reached in the internal conversion, resulting in a higher cis-isomer quantum yield.

Theoretical study of excited state dynamics of a ratiometric fluorescent probe for detection of SO2 derivatives.

Sulfur dioxide (SO2), a toxic air pollutant, can have harmful effects on human health when inhaled or when it forms bisulfite in the body. In the present work, a ratiometric fluorescent probe, 2-(2'-hydroxyphenyl)benzothiazole-3-ethyl-1,1,2-trimethyl-1H-benzo[e]indolium (HBT-EMBI), was selected to study the mechanism of SO2 derivatives detection. This study provides insights into the attributions of ratiometric fluorescence through hydrogen bond dynamics, electronic excitation properties, radiation rates, and excited state intramolecular proton transfer (ESIPT) processes using the density functional theory (DFT) and the time-dependent density functional theory (TDDFT) level. The results confirm that the large Stokes shifts and broad emission spectra of the HBT-EMBI probe are associated with its intramolecular charge transfer (ICT) characteristics and hydrogen bonding-driven ESIPT processes, respectively. After the addition reaction between the probe and HSO3-/SO32-, the conformational populations of HBT-EMBI-HSO3- transfer abnormally from enol configurations to more stable keto configurations, which leads to a distinguished change in the visible color and the ratiometric fluorescence signal, and is not due to the blockage of the ICT process of HBT-EMBI-HSO3-, as previously reported. This work provides a new perspective on the mechanism of detection of SO2 derivatives by ESIPT fluorescent probes.

Implications of TP-positive CAFs in the Bone Invasion of Oral Squamous Cell Carcinoma.

BACKGROUND/AIM: Cancer-associated fibroblasts (CAFs) have recently been suggested as critical cellular components of bone invasion in oral squamous cell carcinoma (OSCC). However, the underlying molecular mechanisms and subtypes related to their bone-invasive function are unclear. This study investigated the implications of thymidine phosphorylase (TP)-positive CAFs (TP+CAFs) in OSCC bone invasion. MATERIALS AND METHODS: TP expression was determined in 116 patients with OSCC using immunohistochemistry. The influence of TP expression on the biological behavior of CAFs was investigated in vitro. The possible impact of TP+CAFs on bone invasion in OSCC was further evaluated using patient-derived xenograft (PDX) mouse models. RESULTS: In bone-invasive OSCC tissues, TP+CAFs were mainly distributed on the surface of resorbed bone tissue rather than on the tumor side. High levels of TP+CAFs were significantly associated with higher T-stage, bone invasion, and worse overall survival and recurrence-free survival in our study cohort. Recombinant human TP promoted the proliferative and invasive abilities of CAFs and increased matrix metalloproteinase-9 mRNA expression in vitro, related to bone resorption. In the PDX mouse models, TP+CAFs were found in early bone resorption on the surface of resorbed bony tissues. Bone resorption occurred more frequently in the PDX models with TP+CAFs than in those without. CONCLUSION: TP+CAFs were significantly associated with bone invasion and the prognosis of OSCC. This study provides insights into cellular and molecular targets for the early diagnosis and treatment of bone-invasive OSCC.

Theoretical study on photoisomerization effect with a reversible nonlinear optical switch for dithiazolylarylene.

DFT and TDDFT methods have been performed to investigate the photoisomerization effect for dithiazolylarylene on solution. The weak S···N interaction and CH···N hydrogen bond restrain the rotation of the side-chain thiazolyl ring in open-isomer 1a, the higher stability of which prefers to show a high quantum yield of photoisomerization. The calculated UV-Vis spectrum at around 320 nm for open-isomer 1a is bathochromically shifted to 647 nm for closed-isomer 1b, in excellent agreement with the experimental photochromic phenomenon. The electron transition in ECD (electron circular dichroism) spectra for closed-isomer 1b with two chiral carbon atoms is dominated by ICT (intramolecular charge transition) and LE (local excitation) corresponding to one positive (440 nm) and one negative Cotton effect (650 nm), respectively, where the two chiral carbon atoms play a slight role in these transitions. The PES in the S(1) and S(0) states, respectively, indicates that the cyclization reaction from open-isomer 1a to closed-isomer 1b is allowed in the photoexcited state with high-conversion quantum efficiency, while it is forbidden in the thermodynamic process. In addition, the second-order nonlinear optical response for closed-isomer 1b is nearly six times larger than that for open-isomer 1a. It is also confirmed that the photoirradiation evokes the photoisomerization character to show dramatic difference in the second-order NLO response, which can be applied to designing photochromic materials and reversible NLO switches.

Nonadiabatic ab initio molecular dynamics of photoisomerization in bridged azobenzene.

The photoisomerization mechanisms of bridged azobenzene are investigated by means of surface hopping dynamics simulations based on the Zhu-Nakamura theory. In the geometry optimizations and potential energy surface calculations, four minimum-energy conical intersections between the ground state and the lowest excited state are found to play important roles in the trans-cis and cis-trans isomerization processes. The trans-cis photoisomerization proceeds through two minimum-energy conical intersections. Ultrafast pedal motion of the N atoms and twisting of phenyl rings around their N-C bonds allows the molecule to move to a minimum-energy conical intersection, after which surface hopping from S(1) to S(0) occurs. In the S(0) state, further rotation occurs around the N=N bond and two N-C bonds until the azo moiety and phenyl rings complete their isomerization. Finally, the cis form is achieved by subsequent adjustment of the ethylene bridge. In the cis-trans photodynamics, there is one rotational pathway, in the middle of which two CIs are responsible for the surface hopping to the S(0) state. After the nonadiabatic transition, the molecule reaches the trans form through a barrierless pathway and the two phenyl rings and the additional bridge complete their reorientation almost at the same time.

[The study of vibrational spectra of 3-amino-2, 5-dichlorobenzoic acid by density functional theory].

To understand the relationship between the vibrational spectra and the geometry structure of 3-amino-2, 5-dichlorobenzoic acid (3A2, 5DBA) essentially, geometry optimizations and vibrational frequencies calculation of 3A2, 5DBA were performed at Hartree-Fock (HF) and Becke's three-parameter hybrid functional (B3) for the exchange part and the Lee-Yang-Parr (LYP) correlation function (B3LYP) level using 6-311G(d, p) basis set, respectively. The structural information and 45-complete normal vibrational modes of 3A2, 5DBA were obtained. Comparing the computational geometric parameters of 3A2, 5DBA with the values observed in experimental measurement of benzoic acid as well as the computed vibrational frequencies of 3A2, 5DBA with the reported data of pertinent literature, it was revealed that the results coming from B3LYP/6-311G(d, p) are more reasonable than those by HF/6-311G(d, p). Taking into account the difference between the computed 3A2, 5DBA molecule and the experimental measured sample, the calculated vibrational frequencies were reasonably scaled. Under the B3LYP/6-311G(d, p) method, the scale factor was 1.0013 for the vibrational frequencies with wave numbers <800 cm(-1), while the scale factor was 0.9613 for the vibrational frequencies with wave numbers >800 cm(-1). With the help of Gaussian View software package, the theoretically calculated vibrational frequencies were assigned much more accurately. In addition, the vibrational analysis of substitutive groups and main functional groups of 3A2, 5DBA was carried out. Through the comparison of the calculated vibrational frequencies with the frequencies of 3A2, 5DBA observed in FTIR experiment, the authors found that the theoretically calculated vibrational frequencies scaled reasonably were in excellent agreement with the data coming from experimental measurements. Meanwhile, according to the related literature reports, it was shown that our work done in the paper about vibrational assignments and vibrational analysis of 3A2, 5DBA turned out to be reasonable.

CDCA5 is negatively regulated by miR-326 and boosts ovarian cancer progression.

PURPOSE: Ovarian cancer (OC) is the fifth leading cause of cancer death in women and one of the most prevalent malignancies in humans. Therefore, improved methods for OC early detection are urgently needed. Research has demonstrated that microRNAs (miRs) are strongly linked to OC tumorigenesis. The potential regulatory mechanism regarding miR-326 in OC is undefined. The present study was aimed to explore miR-326 expression in OC and its roles in OC progression. METHODS: Qualitative (q)RT-PCR was adopted to examine miR-326 expression in OC tissues and cell lines in clinical samples. qRT-PCR and Western blot were applied to detect division cell cycle associated 5 (CDCA5) expression at the messenger RNA (mRNA) and protein levels. CCK-8 and Transwell invasive experiments were utilized to examine cell proliferation and invasion. Cell cycle and apoptosis were analyzed by flow cytometry. Online bioinformatics analysis was employed to predict the target genes of miR-326 and luciferase reporter genes were applied for validation. RESULTS: MiR-326 was remarkably down-regulated in OC tissues and cell lines relative to the corresponding adjacent normal tissues and normal human ovarian surface epithelial cells (HOSE). MiR-326 overexpression markedly restrained the proliferation and invasion of OC cells, whereas miR-326 inhibitors exerted the contrary effect. Additionally, miR-326 up-regulation in OC cells prevented cells from entering S-phase and enhanced apoptosis, a phenomenon that may be due to CDCA5 down-regulation. Furthermore, we proved that CDCA5 was a downstream target of miR-326. CONCLUSIONS: MiR-326 represses the proliferation and invasion of OC cells and enhances apoptosis by specifically modulating CDCA5 expression.

Prediction of Chemosensitivity in Multiple Primary Cancer Patients Using Machine Learning.

BACKGROUND/AIM: Many cancer patients face multiple primary cancers. It is challenging to find an anticancer therapy that covers both cancer types in such patients. In personalized medicine, drug response is predicted using genomic information, which makes it possible to choose the most effective therapy for these cancer patients. The aim of this study was to identify chemosensitive gene sets and compare the predictive accuracy of response of cancer cell lines to drug treatment, based on both the genomic features of cell lines and cancer types. MATERIALS AND METHODS: In this study, we identified a gene set that is sensitive to a specific therapeutic drug, and compared the performance of several predictive models using the identified genes and cancer types through machine learning (ML). To this end, publicly available gene expression datasets and drug sensitivity datasets of gastric and pancreatic cancers were used. Five ML algorithms, including linear discriminant analysis, classification and regression tree, k-nearest neighbors, support vector machine and random forest, were implemented. RESULTS: The predictive accuracy of the cancer type models were 0.729 to 0.763 on the training dataset and 0.731 to 0.765 on the testing dataset. The predictive accuracy of the genomic prediction models was 0.818 to 1.0 on the training dataset and 0.759 to 0.896 on the testing dataset. CONCLUSION: Performance of the specific gene models was much better than those of the cancer type models using the ML methods. Therofore, the most effective therapeutic drug can be chosen based on the expression of specific genes in patients with multiple primary cancers, regardless of cancer types.

Hybridized nanolayer modified Ω-shaped fiber-optic synergistically enhances localized surface plasma resonance for ultrasensitive cytosensor and efficient photothermal therapy.

Inadequate sensitivity and side-effect are the main challenges to develop cytosensors combining with therapeutic potential simultaneously for cancer diagnosis and treatment. Herein, localized surface plasma resonance (LSPR) based on hybridized nanolayer modified Ω-shaped fiber-optic (HN/Ω-FO) was developed to integrate cytosensor and plasmonic photothermal treatment (PPT). On one hand, hybridized nanolayers improve the coverage of nanoparticles and refractive index sensitivity (RIS). Moreover, the hybridized nanoploymers of gold nanorods/gold nanoparticles (AuNRs/AuNPs) also result in intense enhancement in electronic field intensity (I). On the other hand, Ω-shaped fiber-optic (Ω-FO) led to strong bending loss in its bending part. To be specific, a majority of light escaped from fiber will interact with HN. Thus, HN/Ω-FO synergistically enhances the plasmonic, which achieved the goal of ultrasensitive cytosensor and highly-efficient plasmonic photothermal treatment (PPT). The proposed cytosensor exhibits ultrasensitivity for detection of cancer cells with a low limit of detection down to 2.6 cells/mL was realized just in 30 min. HN/Ω-FO-based LSPR exhibits unique characteristics of highly efficient, localized, and geometry-dependent heat distribution, which makes it suitable for PPT to only kill the cancer cells specifically on the surface or surrounding fiber-optic (FO) surface. Thus, HN/Ω-FO provides a new approach to couple cytosensor with PPT, indicating its great potential in clinical diagnosis and treatment.

Sensing mechanism of a ratiometric near-infrared fluorescent chemosensor for cysteine hydropersulfide: Intramolecular charge transfer.

Previous studies have shown that the cysteine hydropersulfide (Cys-SSH) as the sulfur donor is crucial to sulfur-containing cofactors synthesis. Recently, a selective and sensitive near-infrared ratiometric fluorescent chemosensor Cy-DiSe has been designed and synthesized to detect Cys-SSH spontaneously. Herein, by means of the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) approaches, the sensing mechanism has been thoroughly explored. According to our calculations, the experimental data have been reproduced. The results indicate the intramolecular charge transfer (ICT) is the reason for changes in fluorescence wavelengths. Compared with the chemosensor Cy-DiSe, the larger energy gap of Cy induced by ICT mechanism leads to the blue-shift of the absorption and emission spectra, which guarantees that Cy-DiSe can become a ratiometric fluorescent chemosensor to detect Cys-SSH.

Volume-conserving photoisomerization of a nonplanar GFP chromophore derivative: Nonadiabatic dynamics simulation.

Nonadiabatic dynamics of a nonplanar green fluorescent protein (GFP) chromophore derivative was examined theoretically by trajectory surface hopping approach at the CASSCF level based on Zhu-Nakamura theory. The geometry optimizations show that there are four ground-state minima and four conical intersections between the ground (S0) and first excited (S1) states. Four S1-state minima were found at a perpendicularly twisted conformation around the imidazolinone-bridged bond. Upon excitation to S1 state, the main decay pathways of four isomers involve different S0/S1 potential energy surface conical intersections. The dominant excited-state relaxation mechanism of this GFP chromophore derivative is the twists of two bridging bonds and the methyl group in the bridge combined with the pyramidalization character of the central carbon atom. Further twists of two bridging bonds and the methyl group occur sequentially in the S0 state. It is worth to mention that the special volume-conserving motion of this molecule is attributed to twists of two bridging bonds in the same direction during the whole photoisomerization processes. The theoretical investigation presented herein provides important insights into the volume-conserving photoisomerization mechanisms of a nonplanar GFP chromophore derivative. We believe that the present work can benefit the design of the photochromic molecule devices in confined media.

Nonadiabatic dynamics simulation of photoisomerization mechanism of the second stablest isomer of N-salicilydenemethylfurylamine.

The photoisomerization processes of the second stablest isomer in the aromatic Schiff base, N-salicilydenemethylfurylamine, in the gas phase have been studied by static electronic structure calculations and surface-hopping dynamics simulations based on the Zhu-Nakamura theory. Various stable structures are obtained in the optimization because of different orientations of methyl-furyl part with respect to the salicylaldimine part and different orientations of hydroxy group with respect to the benzene ring. Upon photoexcitation into the first excited state, bond isomerization in the salicylaldimine part is completely suppressed until the strong excited-state hydrogen bond is broken. The decay pathway involves two excited-state minima, one in cis-enol form and the other in cis-keto form. After the excited-state proton transfer, twists of bonds lead to a conical intersection between the ground and excited states. After internal conversion around a conical intersection, the molecule is stabilized in cis- or trans-keto form. If the reverse hydrogen transfer process occurs in the ground state, the molecule will finally end up in the cis-enol region. The cis-keto and trans-keto isomers are observed as photoproducts. According to our full-dimensional nonadiabatic dynamics simulations, we find the excited-state intramolecular proton transfer and torsions of three single bonds in the chain to be responsible for photoisomerization of the second stablest isomer of N-salicilydenemethylfurylamine.

Photoisomerization mechanism of 1,1'-dimethyl-2,2'-pyridocyanine in the gas phase and in solution.

The trans→cis and cis→trans photoisomerization mechanisms of 1,1'-dimethyl-2,2'-pyridocyanine have been investigated theoretically in the gas phase and in methanol. Two-dimensional potential energy surfaces were computed for the ground and first excited singlet states of the isolated molecule using complete active space self-consistent field method. Our computations suggest that the torsion around the central C-C bonds with carbon-out-of-plane motion is the preferred photoisomerization mechanism. In the gas phase, conical intersections were found near the minima of excited state. The excited-state decay follows a barrierless minimum-energy pathway before the molecule moves to the excited-state global minimum (minS1) and the system relaxes to the ground state through a conical intersection. In methanol, the system would first reach a stationary structure of C2 symmetry after the trans form is electronically excited. Solvent polarity effects were investigated in chloroform, dichloromethane, 1-propanol, ethanol, methanol, and water. There is a significant barrier between the stationary structure of C2 symmetry and minS1 in the excited state in high polarity solvents. Thus, Me-1122P has a much longer lifetime of the excited state in solvents of high polarity.