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The electronic and vibrational spectra of the meso-tetrakis(4-sulfonatophenyl)-porphyrins (TSPP) have been studied computationally using the PFD-3B functional with time-dependent density functional theory for the excited states. The calculated UV-vis absorption and emission spectra in aqueous solution are in excellent agreement with the experimental measurements of both H2TSPP−4 (monomer) at high pH and H4TSPP−2 (forming J-aggregate) at low pH. Moreover, our calculations reveal an infrared absorption at 1900 cm−1 in the singlet and triplet excited states that is absent in the ground state, which is chosen as a probe for transient IR absorption spectroscopy to investigate the vibrational dynamics of the excited state. Specifically, the S2 to S1 excited state internal conversion process time, the S1 state vibrational relaxation time, and the lifetime of the S1 excited electronic state are all quantitatively deduced. [ABSTRACT FROM AUTHOR]

Following up on our previous work on vibrationally resolved electronic absorption spectra including the effect of vibrational pre-excitation [von Cosel et al., J. Chem. Phys. 147, 164116 (2017)], we present a combined theoretical and experimental study of two-photon-induced vibronic transitions in polyatomic molecules that are probed in the VIbrationally Promoted Electronic Resonance experiment using two-photon excitation (2P-VIPER). In order to compute vibronic spectra, we employ time-independent and time-dependent methods based on the evaluation of Franck–Condon overlap integrals and Fourier transformations of time-domain correlation functions, respectively. The time-independent approach uses a generalized version of the FCclasses method, while the time-dependent approach relies on the analytical evaluation of Gaussian moments within the harmonic approximation, including Duschinsky rotation effects. For the Coumarin 6 dye, two-dimensional 2P-VIPER experiments involving excitation to the lowest-lying singlet excited state (S1) are presented and compared with corresponding one-photon VIPER spectra. In both cases, coumarin ring modes and a CO stretch mode show VIPER activity, albeit with different relative intensities. Selective pre-excitation of these modes leads to a pronounced redshift of the low-frequency edge of the electronic absorption spectrum, which is a prerequisite for the VIPER experiment. Theoretical analysis underscores the role of interference between Franck–Condon and Herzberg–Teller effects in the two-photon experiment, which is at the root of the observed intensity distribution. [ABSTRACT FROM AUTHOR]

UV-induced processes are commonly studied in acetylacetone analogues. In this contribution, we revisit the existing work on the photoisomerization process in some of the fluorinated analogues of acetylacetone, i.e., trifluoroacetylacetone (F3-acac) and hexafluoroacetylacetone (F6-acac). We performed selective UV laser excitation of these molecules trapped in soft cryogenic matrices, namely neon and para-hydrogen, and probed by vibrational spectroscopy. Clear spectroscopy of 3 isomers of F6-acac and 6 isomers of F3-acac is obtained, including the first characterization of a second open enol isomer of hexafluoroacetylacetone. In addition, we present the electronic absorption spectra of both molecules in cryogenic matrices before and after specific UV irradiations, giving new data on the electronic transitions of photoproducts. Vibrational and electronic experimental results are analyzed and discussed within comparisons with DFT and TD-DFT calculations. Our findings contribute to a deeper understanding of the photoisomerization process in these molecules after electronic excitation in gas and condensed phase. [ABSTRACT FROM AUTHOR]

In the present paper, we study the interaction of associates (dimers and trimers) of 4-n-pentyl-4΄-cyanobiphenyl (5CB) with 1, 2-Diamino-4-nitrobenzene and N, N-Dimethyl-4-nitrosoaniline dye molecules. The structures of the intermolecular complexes were studied using hybrid functionals of the DFT method M06 and B3LYP with the 6–31 + G (d) basis set. The intermolecular binding energy of dyes with associates depends on the structure of the complexes and is about 5 kcal/mol. Vibrational spectra were calculated for all intermolecular systems. The electronic absorption spectra of dyes are sensitive to the structure of the mesophase. The pattern of the spectrum changes depending on the structure of the complex of the dimer or trimer with the dye molecule. The long-wavelength transition bands are characterized by shifts that are bathochromic for 1, 2-Diamino-4-nitrobenzene and hypsochromic for N, N-Dimethyl-4-nitrosoaniline. [ABSTRACT FROM AUTHOR]

Phenol derivatives are interesting molecules for theoretical studies due to their relatively small size and similarity to organic species. 2,6-dibromo-4-nitrophenol was investigated by using density functional theory (DFT). XRD data and optimized DFT studies are found to be in good correspondence with each other. Analysis of title compound was obtained by B3LYP/6-31 + G(d,p) level of theory to explain the vertical transactions. Calculated FT-IR and FT-Raman results are found to be in good agreement with experimental FT-IR and FT-Raman findings. Natural bond theory (NBO) study was also performed using B3LYP/6-31 + G(d,p) method. Correlations between the proton and carbon-13 experimental chemical shifts and the GIAO NMR calculations are in good agreement and these values have been used for the definitive signal assignments to the corresponding structures. Electronic absorption spectra of DBNP has been calculated by using CIS-DFT method based on the B3LYP/6-311++G (d,p) level of the optimized structure in gas phase. [ABSTRACT FROM AUTHOR]

New spectroscopic parameters have been calculated to aid in the laboratory and observational detection of AlCH, AlCH+, MgCH, MgCH+, and their deuterated analogs. All species exist in linear geometry except for AlCH+, which exhibits a bent structure. Rotational frequencies have been calculated and the transition with maximum intensity is discussed for three temperature regions present in space: 100 K for a central circumstellar envelope (CSE), 30 K for an outer CSE, and 3 K indicative of the interstellar medium. Pertinent frequencies range from 25 to 250 GHz, depending on the species. At 30 K, the most intense transition is expected to be J = 4 → 3 for all species. The vibrational spectrum of each molecule is expected to be complicated due to the flat nature of the potential energy surface along the bending angle and the presence of anharmonic resonances. Deuteration produces a decrease in vibrational frequency, which may be utilized in experiments to confirm detection of these molecules. The electronic absorption spectrum of both AlCH and MgCH is predicted to be congested and broad. Various high-oscillator-strength transitions are predicted. Upon photoexcitation in the 220–300 nm region, facile dissociation on a repulsive excited state along the Al–C coordinate is predicted to be a source of Al in the colder regions of space. Photodissociation of MgCH requires several nonradiative processes that will control the product state distribution of the fragments. [ABSTRACT FROM AUTHOR]

[Display omitted] • The rotationally resolved absorption spectrum of A ∼ 2Σ+– X ∼ 2Π 3/2 for ICN+ was observed. • The rotational constants of both the electronic states were precisely determined. • The rotational constants of FCN+, ClCN+, and BrCN+ were theoretically evaluated. • The rotational profiles of ClCN+ were simulated to identify this cation in space. A rotationally resolved gas-phase absorption spectrum of the A ∼ 2Σ+– X ∼ 2Π 3/2 electronic transition of the cyanogen iodide radical cation ICN+ was observed by cavity ring-down spectroscopy for the first time. This cation was produced in a supersonic planar discharge jet through a mixture of ICN in helium. By the aid of a program for rotational, vibrational and electronic spectra PGOPHER, the rotational constants were determined to be 0.10700(12) and 0.11002(12) cm−1 for the A ∼ 2Σ+ and X ∼ 2Π 3/2 electronic states, respectively, and the band origin to be 18262.083(3) cm−1. The rotational constant ratio β {= (B ′− B ″)/ B ″} was determined to be −2.8%. The β values for FCN+, ClCN+, BrCN+, and ICN+ were also evaluated theoretically by CAM-B3LYP/CEP-121G using Gaussian 09W. The rotational profile of the absorption band and its temperature dependence for ClCN+, one of the important candidates for Diffuse Interstellar Bands, were simulated, aiding us in the identification of this cation as in interstellar space. [ABSTRACT FROM AUTHOR]

The alkylammonium halogenocobalate families are subjected to diverse studies according to their wide field application. In this work, the [(C 3 H 7) 4 N] 2 CoBr 4 compound was synthesized using a slow evaporation solution growth method at room temperature and characterized by X-ray powder diffraction (XRPD) and UV-VIS-IR absorption spectrometry. The X-ray powder diffraction (XRPD) data confirmed the formation of a single-phase with monoclinic system (C2/c space group). The optical absorption and reflectance spectra of the named compound were measured at the range [240 nm–1900 nm] at room temperature. Using three methods, we have determined the direct optical band gap estimated at 3.8 eV and the Urbach energy. Different models were used to calculate the refractive index, which was found to be in the range of 2.12–2.58. This spectrum consists also of electronic transition d-d of Co2+ (3 d7) ions. This work examines a detailed crystal-field analysis of the UV–Vis–NIR lines associated to the transitions between the Stark levels of Co2+, occupying a T d site symmetry in [CoBr 4 ]2- (organic part). The theoretical study is based on the Racah tensor algebra methods. This analysis permits us to determine the electronic structure of the cobalt ion Co2+ based on the crystal field theory. As a result, Racah and crystal-field parameters have been reliably obtained. A good agreement between the theoretical and the experimental energy levels are obtained. This theoretical study confirms the T d site symmetry of Co2+ in [CoBr 4 ]2- and leads to a satisfactory correlation between experimental and calculated energy levels. In addition to internal transitions, the absorption spectrum shows vibrational peaks witness of anharmonic behavior. • Absorption and reflectance spectra were measured. • Optical band gap, Urbach energy, extinction coefficient and refractive index were determined. [ABSTRACT FROM AUTHOR]

This study reports the spectroscopic characterization and second hyperpolarizability of the odd spin states of acetonitrile at B3LYP/aug-cc-pVDZ level of theory. The spectroscopic parameters studied in gas phase and water solvent. Upon changes of spin states of acetonitrile significant changes are observed in the spectroscopic study. Natural transition orbitals (NTOs) study also reported for acetonitrile in gas phase and water solvent. From nonlinear optical study it is observed that second hyperpolarizability of odd spin states of acetonitrile are more responsive than the first hyperpolarizability. [Display omitted] • Spectroscopic study of odd spin state of acetonitrile in gas and water solvent reported. • The solvent effect taken in to the consideration for the study using IEFPCM model. • The Natural transition orbital studied for the acetonitrile in gas phase and in water solvent. • An increase in field strength decreases the HOMO to LUMO gap in gas and solvent acetonitrile. • Thorough nlo study confirmed acetonitrile is more responsive to 2nd hyperpolarizability than 1st. The present study reports the spectroscopic characterization and second hyperpolarizability of odd spin states of acetonitrile in gas phase and water solvent. The odd spin states of acetonitrile are singlet, triplet and quintet spin state of acetonitrile have been considered for the study. The spectroscopic characterization viz. energy, geometrical parameters, infrared and electronic absorption spectra, molecular orbitals (MOs) their energies and natural transitions orbitals (NTOs) in gas phase and water solvent state reported at B3LYP/aug-cc-pVDZ level of theory. The second hyperpolarizability values are obtained using various methods and basis sets for comparison. It has been observed that the second hyperpolarizability values for the odd spin states of acetonitrile are more positive than the first hyperpolarizability. It is clearly seen that the effect of spin on spectroscopic parameters except on energy. The singlet gas phase acetonitrile calculations are well matching with the available experimental determinations. The TDDFT approach has been used to study electronic absorption spectra of all spin states of acetonitrile in gas phase and in water solvent. The IEFPCM model implemented in studying acetonitrile in water solvent at B3LYP/aug-cc-pVDZ level of theory. It is observed that HOMO to LUMO gap is larger for singlet than the triplet and quintet spin state and it decrease with an increase in strength of an applied field. All these calculations performed using Gaussian 16 program package. [ABSTRACT FROM AUTHOR]