Vapor-Phase Raman Spectra, Theoretical Calculations, and the Vibrational and Structural Properties of cis- and trans-Stilbene

Abstract

The vapor-phase Raman spectra of cis- and trans-stilbene have been collected at high temperatures and assigned. The low-frequency skeletal modes were of special interest. The molecular structures and vibrational frequencies of both molecules have also been obtained using MP2/cc-pVTZ and B3LYP/cc-pVTZ calculations, respectively. The two-dimensional potential map for the internal rotations around the two Cphenyl-C(═C) bonds of cis-stilbene was generated by using a series of B3LYP/cc-pVTZ calculations. It was confirmed that the molecule has only one conformer with C2 symmetry. The energy level calculation with a two-dimensional Hamiltonian was carried out, and the probability distribution for each level was obtained. The calculation revealed that the "gearing" internal rotation in which the two phenyl rings rotate with opposite directions has a vibrational frequency of 26 cm(-1), whereas that of the "antigearing" internal rotation in which the phenyl rings rotate with the same direction is about 52 cm(-1). In the low vibrational energy region the probability distribution for the gearing internal rotation is similar to that of a one-dimensional harmonic oscillator, and in the higher region the motion behaves like that of a free rotor.

Ab Initio Excited-State Transient Raman Analysis

“…To demonstrate the capability of the transient Raman protocol presented here to realistically capture the temporal evolution of a vibrational mode, we have computed the transient nonresonant Raman signals following a vertical electronic excitation in the trans -stilbene (Figure ) molecule, which has been extensively studied from both the experimental and theoretical vantage. − …”

Ground-State Geometry and Vibrations of Polyphenylenevinylene Oligomers

“…This is consistent with very small deplanarization energy gain (if any), so that intermolecular steric interactions easily planarize the molecules. Taking into account large uncertainty of experimental determination of BLA and dihedrals, vibrational spectroscopy becomes an important tool for indirectly probing the geometry of PPV oligomers using both empirical − and first-principles − ,, models to match experimental spectra. − For the high-frequency region (>400 cm –1 ), Raman spectra of PPV are well reproduced by harmonic approximation with scaled DFT frequencies. They are dominated by two strong Raman bands: , the band at 1600 cm –1 corresponds to the BLA mode (alternating stretching of bonds), whereas the band at 1200 cm –1 has a more complex nature.…”

Spin crossover metal–organic frameworks with inserted photoactive guests: on the quest to control the spin state by photoisomerization

“…Raman spectra of 2 and 3 contain several intense peaks that can be assigned to stilbene guest molecules on the basis of literature data. 25,29,30 An intense Raman peak, corresponding to vinyl C=C stretching vibrations, appears for both isomers at ca. 1630 cm -1 (though less intense and redshifted in the cis isomer).…”

“…25a,30 Other weak intensity peaks originating from stilbene were found between 1300 and 1500 cm -1 corresponding to C-H bending and C=C stretching vibrations of phenyl rings. 30 One can differentiate the two isomers using a weak intensity peak at ca. 960 cm -1 (identified as in-phase ethylenic C-H out-of-plane wagging vibration) 30,31 which is only present in the cis configuration, due to its nonplanar structure.…”

“…30 One can differentiate the two isomers using a weak intensity peak at ca. 960 cm -1 (identified as in-phase ethylenic C-H out-of-plane wagging vibration) 30,31 which is only present in the cis configuration, due to its nonplanar structure.…”