Vibrational spectra of cis-stilbene and 1,1-diphenylethene (original) (raw)
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Infrared and Raman spectra of cis-stilbene and its deuterated isotopomers
Journal of Molecular Structure, 1995
The vibrational analysis of cis-stilbene in the ground electronic state based on the infrared and Raman spectra of a series of its isotopomers and scaled semiempirical AM1 calculations is reported. The CαCα stretching, all the four CαH deformations and the CαCα torsion are described. A comparison with trans-stilbene shows a much lesser degree of couplings between olefinic and phenyl vibrations
Spectrochimica Acta Part A: Molecular Spectroscopy, 1987
Raman and i.r. spectra of 1,l'diphenylethene and the low-frequency spectra of benzophenone, diphenylketimine, diphenylmethane and diphenylether have been reinvestigated in order to attain a consistent attribution of the characteristic vibrations of geminal diphenyl substitution. Most of the internal vibrations of the benzene rings were seen in pairs of bands with very close frequencies, corresponding to symmetric (in-phase) and asymmetric (out-of-phase) modes. Of those monosubstituted-benzene vibrations usually considered to be sensitive to substitution, v,s, vs, and vIeb were found to span a narrow frequency interval, with a separation of l&20 cm-r between the respective symmetric and asymmetric modes. On the contrary, quite far apart frequencies were attributed to the symmetric and asymmetric modes of the vrbrattons vr, vgb and vIot,; for these, frequency separations ranging from about 50 to 140 cm-' were found, with a pronounced dependence of the covered spectral interval on the nature of the central group. The presence of a very strong Raman band at 9&80 cm-' was the most striking spectral characteristic for all of the molecules under consideration: it was attributed to the Ph-X-Ph angle bending vibration, although considerable mixing of it with other low-frequency vibrations was considered likely. Based on internal potential energy functions computed by a semikmp&al method (C-INDO), an approximate calculation of the frequencies for the conrotatory torsion of Ph,CCH,, Ph,CO and Ph,O and both torsions of Ph,CH, & was performed, so as to predict their relative magnitude&d t-0 assist the interpretation of the spectra in the lowest region. 1.r. bands observed at 55 and 70 cm-1 for Ph20 and Ph*CO, respectively, might be considered for assignment to torsional vibrations.
The Journal of Physical Chemistry, 1994
Time-resolved resonance Raman spectra are reported for the lowest excited triplet state of stilbene and three of its isotopomers. The spectra were obtained using a two-laser pump-and-probe arrangement under various experimental conditions. The spectrum of trans-stilbene after direct excitation in a glassy medium at low temperature (glycerol at 203 K) is compared with that of cis-stilbene under sensitized excitation in solution at room and low temperature. The dependence of resonance Raman spectra on excitation wavelength in both cases is investigated. The observed spectra and isotopic shifts are discussed and interpreted on the basis of quantum chemical molecular orbital calculations. Optimized geometries and vibrational frequencies in the T1 state are calculated by a semiempirical QCFF/PI Hamiltonian and by means of R O H F a b initio methods using the 6-31G basis set. TIT , transition energies and moments are calculated using QCFF/PI and CNDO/S methods, and the triplet-triplet transition responsible for the observed T1-T, absorption and resonance Raman spectra is identified as theT1-Tlo transition. Corresponding resonance Raman intensities arecalculated by QCFF/PI. It is concluded that trans-and cis-stilbene adopt a common equilibrium geometry in the TI state, with the ethylenic C=C bond of the ground state being weakened to a bond with essentially single-bond character in the T1 state. The observed spectra in the glass are assigned to a planar geometry, implying that a relative minimum is found at a planar trans geometry (C2h point group) on the potential energy surface of the T1 state. A number of observed non-totally symmetric vibrational modes are tentatively assigned to combinations of either a,, or b, modes, deriving their intensities from relatively large frequency changes upon T1-Tlo excitation. I. Introduction Stilbene (1,2-diphenylethylene) is widely used as a model in studies of C=C double-bond isomerization. The E-2 (trans cis) photoisomerization of stilbene has been reviewed in detail.'-5 Structure and dynamics on the stilbene SI potential energy surface (PES) have been studied in a number of papers."I7 The SO and S1 states of (E)-and (Z)-stilbene have been studied by Raman and resonance Raman (RR) spectroscopies,18-26 as have their anion27-30 and cation31 radicals. Structure and dynamics on the TI PES have been studied by time-resolved optical absorption and emission spectro~copy,3~-34 by optically-detected magnetic resonance35 (in a single crystal at 1.3 K), and recently by time-resolved RR spectroscopy.36 The spectroscopic triplet energy of the TI state has been determined as 51.0 kcal/mol for @)-stilbene and 55.5 kcal/mol for (Z)-stilbene; therelaxed triplet energy measured by photoacoustic calorimetry is 46.5 kcal/mol for @)-stilbene and 42.0 kcal/mol for (ZJ-stilbe11e.3~ Giirner and Sch~lte-Frohlinde3233~ studied the TI state of stilbene by optical absorption methods. At room temperature, a structureless TIT , absorption spectrum, identical for (E)and (2)-stilbene and increasing monotonically from 400 nm down to the experimental limit of 355 nm, was observed only in the presence of a sensitizer. In Ar-saturated methanol solution at 298 K, the triplet lifetime was 62 ns for @)-stilbene and 60 ns
The vibrational structure of (E,E′)-1,4-diphenyl-1,3-butadiene
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2006
The title compound (DPB) was investigated by FT-IR spectroscopy in liquid solutions and by FT-IR linear dichroism (LD) measurements on samples aligned in stretched polyethylene. The LD data provided experimental assignments of molecular transition moment directions and vibrational symmetries for more than 40 vibrational transitions. The observed IR wavenumbers, relative intensities, and polarization directions were generally well reproduced by the results of a harmonic analysis based on B3LYP/cc-pVTZ density functional theory (DFT). The combined experimental and theoretical results led to proposal of a nearly complete assignment of the IR active fundamentals of DPB, involving reassignment of a number of transitions. In addition, previously published Raman spectra of DPB were well predicted by the B3LYP/cc-pVTZ calculations.
Journal of Molecular Structure, 2013
Infrared spectra (3600-500 cm À1) of gas, amorphous, crystalline solid and Raman spectra (3000-200 cm À1) of liquid and solid were recorded. Variable temperature Raman spectra (30 to À38°C) of liquid were recorded which indicates the presence of significant amounts of six conformers at ambient temperature. Rotation about CAC bond gives Trans (T) and Gauche (G) conformers and rotation around both CAP bonds gives trans (t) and gauche (g) forms. Enthalpy differences for five of the lower energy conformers w.r.t. the lowest energy tTt form were determined to be 272 ± 39 cm À1 , 434 ± 40 cm À1 , 443 ± 30 cm À1 , 663 ± 60 cm À1 and 671 ± 34 cm À1 for g 0 Tt, g 0 Tg 0 , g 0 Tg, tG 0 g 0 and tG 0 t conformers, respectively, which are in the increasing order of energy. Ab initio calculations with various basis sets up to aug-cc-pVTZ were performed and to support the spectroscopic studies MP2(full)/6-31G(d) was used to predict Raman activities, infrared intensities, vibrational frequencies and band contours. By utilizing the previously reported microwave rotational constants along with MP2(full)/6-311+G(d,p) predictions, adjusted r 0 parameters were obtained for two Trans and two Gauche (CAC bond) conformers. The determined heavy atom structural parameters for g 0 Tt [ g 0 Tg 0 ] {tG 0 g 0 } |tG 0 t| conformers are: distances (Å) P 1 AC 2 = 1.870(3) [1.866(3)] {1.858(3)} |1.859(3)|, C 2 AC 3 = 1.535(3) [1.536(3)] {1.534(3)} |1.536(3)|, C 3 AP 4 = 1.863(3) [1.866(3)] {1.866(3)} |1.859(3)|, and angles (°) \P 1 C 2 C 3 = 110.5(5) [110.4(5)] {117.0(5)} |118.5(5)|, \C 2 C 3 P 4 = 115.5(5) [110.4(5)] {113.7(5)} |118.5(5)|. The results are discussed and compared to the corresponding properties of some similar molecules.
Dynamic solvation of charge-distribution rearrangements is often described using a harmonic solvent coordinate. It is not a priori clear whether such a solvent coordinate has a real physical meaning. We have studied five polar organic liquids benzonitrile, benzyl alcohol, N,N-dimethylformamide, ethylene glycol, and glycerol triacetate with high-resolution high signal-to-noise ultrafast optical heterodyne-detected Raman-induced optical Kerr effect spectroscopy OHD-RIKES. The data, converted to the frequency domain, were analyzed entirely with a multimode Brownian-oscillator model. The infrared spectra of the same five liquids were obtained with a combination of terahertz spectroscopy and Fourier-transform infrared spectroscopy. The Brownian-oscillator fits to the OHD-RIKES spectra could be converted successfully to IR spectra by using a simple theoretical model and by keeping all Brownian-oscillator parameters the same except for the amplitudes. This suggests that there is a small set of harmonic oscillators describing ultrafast solvent nuclear dynamics that can be used to understand solvation, IR absorption, and Raman scattering spectra.
Chemical Physics, 1999
Ž. Ž. Raman spectra of the n C[C stretching mode of phenylacetylene PA dissolved in different solvents: methylcyclohexs ane, acetonitrile and benzene in frozen matrices at 77 K as a function of concentration have been recorded and compared with the spectra in the liquid phase. The optical measurements were complemented by the differential scanning calorimetry Ž. DSC scans. The results reveal some dramatic changes with solvent and concentration and are of potential relevance both to fundamental condensed phase modelling and to liquid crystal technology. We have discussed the origin of the splitting Ž. Ž. observed for the n C[C stretching mode of phenylacetylene PA and we have found that H-bond interactions are s responsible for the observed substructure in the vibrational spectra. We have found a glass-like transition at 183 K and two melting-like transitions at 200 and 218 K for PA in acetonitrile. In methylcyclohexane a melting transition starts at 120 K, and does not change in PA solution in contrast to PA in acetonitrile. The DSC scan for PA in methylcyclohexane shows additional phase transition at about 220 K.
Vibrational relaxation of diphenylacetylene at low temperatures
Chemical Physics, 1998
Ž. Raman spectra of the n C[C stretching mode of diphenylacetylene dissolved in acetonitrile and methylcyclohexane S have been recorded at room temperature and 77 K. The results on vibrational dynamics in liquids at room temperature are compared with those at low temperatures at 77 K. Substantial narrowing of spectra at low temperatures leads to revealing vibrational structure. The results given in this paper are a spectacular example of monitoring structural order going from liquid solutions to frozen matrices at low temperatures by Raman spectroscopy. q 1998 Elsevier Science B.V.