Study Of Electronic Absorption Spectra Research Articles

Optical properties of para‐oligophenylenes: A case study of electronic absorption spectrum and relaxation dynamics of terphenyl

AbstractWe present a detailed quantitative description of vibronic‐coupling effects on the singlet photophysics of para‐oligophenylenes. Four energetically close‐lying singlet states (S1, S2, S3, and S4) are taken into consideration to interpret the first UV/Vis absorption band of these molecules. As a representative example, the energetics of those four states are evaluated for para‐terphenyl by performing extensive electronic structure calculations within the linear vibronic coupling framework. We obtain absorption spectral profiles by wavepacket propagation technique using the multi‐configuration time‐dependent Hartree method. Computed spectral profiles are in accord with the experiment. A minor electronic population transfer to upper states on a timescale of 10 fs is observed, suggesting the excited‐state nonadiabatic behavior of the molecule. Our findings necessitate the experimental validation of the role of higher states in the spectroscopy and dynamics of photoexcited para‐oligophenylenes.

Excited State Molecular Parameters Determined by Spectral Means

The possibility to characterize the electronic excited state of a spectrally active molecule based only on the solvatochromic study of electronic absorption spectra is demonstrated. The values of the regression coefficients given the contribution of universal interactions to the spectral shift and their theoretically established dependences on the solute molecule microscopic parameters are used. The values of the dipole moment, polarizability, and ionization potential in the ground electronic state of a spectrally active molecule are established by quantum mechanical methods. Two azo dye molecules are chosen in order to exemplify this method.

Study of electronic absorption spectrum of hafnium monobromide molecule in the 550–800 nm region

The electronic absorption spectrum of the HfBr molecule in the 550–800 nm region is studied using the intracavity laser spectroscopy method. The HfBr molecules are produced in plasma formed during a pulse electric discharge in the vapor mixture of hafnium tetrabromide with hydrogen or ammonium. The discharge tube with the mixture is placed in a dye laser cavity. The spectrum recording is conducted with the help of a diffraction spectrograph (resolution power 240000). The high sensitivity of the intracavity method makes it possible to reveal the presence of twenty new bands in the HfBr spectrum with partially resolved rotational structure. By analogy with the HfCl spectrum, the HfBr bands are assigned to the 2Δ3/2–X2Δ3/2 transition. Analysis of the bands is conducted and molecular constants are determined for the ground and excited states:ωe'' = 255.07 cm–1, ωeωe''= 0.86 cm–1, ωe'= 238.31 cm–1, ωeωe'= 1.1 cm–1, B'' = 0.04251 cm–1, B' = 0.04025 cm–1.

Vibrational dynamics and structural investigation of 4‐benzoylpyridine

AbstractThe polarized Raman spectra in different environments along with the IR counterpart of 4‐benzoylpyridine (4‐BOP) were critically analyzed to assign all of its normal modes of vibration. The knowledge of the positions of different excited electronic states (EESs)was obtained from the study of electronic absorption spectra. Measurement of Raman excitation profiles (REPs)of several normal modes was carried out to get insight into structural and symmetry properties of the molecule. All the experimental observations were substantiated and corroborated theoretically by quantum chemical calculations (QCCs). The possibility of exciton splitting of the 1La band has been explored both from theoretical and experimental points of view. Copyright © 2010 John Wiley & Sons, Ltd.

Density functional theory study of electronic absorption spectra and intermolecular interactions of porphyrin–borate complexes

Electronic absorption spectra and intermolecular interactions of complexes formed between meso-tetrakis (1-methylpyridinium-4-yl) porphine (TMPyP) and borates (tetraphenylborate (TPB) anion or fluorinated derivatives of TPB (TFPB, TFMPB)), namely TMPyP–TPB, TMPyP–TFPB and TMPyP–TFMPB, are investigated by density functional theory (DFT) and time-dependent DFT (TDDFT). It is revealed that the frontier molecular orbitals and electronic transitions for TMPyP have varied when TMPyP is incorporated with borates. TDDFT calculated Q (0, 0) and B (0, 0) bands of TMPyP exhibit a large bathochromic shift when TMPyP turns from its monomeric to complexed forms, and the obtained absorption maxima are in good agreement with the experimental data. The extension of C α–C m bonds for TMPyP in complexes leads to the weakened asymmetric C α–C m stretching vibration, and then moves Q x (0, 1) transition to longer wavelengths. The flattening of TMPyP in complexes is suggested to be the main structural origin of the red-shift event. The calculated interaction energies between TMPyP and borates are in the range of 9.13–18.82 kcal/mol with intensity sequence of TMPyP–TPB > TMPyP–TFPB >> TMPyP–TFMPB. The C–H⋯π static attraction is proposed to be mainly responsible for the stability of the complexes.

Vibrational dynamics and structural investigation of 2,2′-dipyridylketone using Raman, IR and UV-visible spectroscopy aided by ab initio and density functional theory calculation

Detailed investigation on the vibrational and electronic spectra has been carried out in order to study various properties of 2,2'-dipyridylketone molecule in its ground and excited electronic states. To get insight into the structural and symmetry features of the molecule, Raman excitation profiles of several normal modes have been analyzed. The polarized Raman spectra in different environments along with their IR counterpart have been critically surveyed and different normal modes have been assigned. The knowledge in regard to the positions of different excited electronic states has been acquired from the study of electronic absorption spectra. All the experimental observations have been substantiated and corroborated theoretically by the quantum chemical calculation. Possibility of exciton splitting of the 1La band has been explored both from theoretical and experimental points of view.

Electronic and fluorescence spectral studies of a novel porphyrin-polypyridyl ruthenium(II) hybrid linked by a butyl chain

The electronic and fluorescence spectroscopic properties of a novel porphyrin-polypyridyl ruthenium(II) hybrid, [C 4-TPP-(ip)Ru(phen) 2](ClO 4) 2 (TPP = 5,10,15,20-tetraphenylporphyrin, ip = imidazo[4,5-f][1,10]phenanthroline and phen = 1,10-Phenanthroline), in which a polypyridyl ruthenium(II) moiety is linked to a porphyrin moiety by a butyl chain have been investigated and compared to its corresponding reference compounds. The studies of electronic absorption spectra have shown that there is an electronic interaction between the porphyrin moiety and the polypyridyl ruthenium(II) moiety in the hybrid. It can be found that intramolecular photoinduced electron and energy transfer processes may occur in the hybrid from the fluorescence spectra. When exciting in Soret band and Q band of porphyrin, the fluorescence quenching of the porphyrin moiety of the hybrid takes place due to electron transfer from the lowest singlet excited state (S 1) to the appended polypyridyl rutherium(II) moiety, while the decay of S 2 (the second-excited singlet state) of the porphyrin moiety is mainly contributed to internal conversion to S 1. When exciting in MLCT band of the polypyridyl ruthenium(II) moiety, fluorescence corresponding to the polypyridyl ruthenium(II) moiety is quenched by intramolecular energy transfer from 3MLCT of the ruthenium moiety to the lowest-energy triplet state localized on the porphyrin moiety.

Multivariate calibration of chlorophyll a using partial least squares and electronic absorption spectroscopy

Partial least squares (PLS) calibration has been applied in the study of electronic absorption spectra of pure chlorophyll a. Inverse univariate calibration was applied separately at each wavelength. The effectiveness of the calibration models was quantitatively expressed as root mean square errors of both calibration and prediction. Wavelengths with the best linear behaviour were selected, and PLS performed on an increasing number of wavelengths, sorted by their prediction efficiency. PLS calibration results in a substantial reduction in the prediction error relative to the best single wavelength result and is an alternative to using molar absorbance (extinction) coefficients.

Conformations privilegiées des sulfures de dithienyles: Étude PAR spectroscopie d'absorption électronique

AbstractThe experimental and theoretical study of electronic absorption spectra (UV) of dithienyl sulfides shows that non planar conformations are favored in vapour phase and in solution. The presence of halogen atoms in positions “ortho” to the junction of the rings induces a very important modification of preferential conformations.