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• The geometry changes of the tgt - and the ttt -rotamer of 1,2-diphenoxyethane have been determined from a combined fit of rotation al constants and fluorescence emission intensities from several vibronic bands. • The geometry changes are compared to the results of ab initio calculations at the spin-component-scaled approximate coupled cluster singles and doubles (CC2) level of theory. • The excitonic splitting of the origins of both rotamers has been determined from ab initio calculations. The geometry changes of the tgt - and the ttt -rotamer of 1,2-diphenoxyethane were determined from a combined fit of line intensities in fluorescence emission spectra, obtained via pumping different vibronic transition, and the changes of rotational constants upon electronic excitation, which were taken from [E.G. Buchanan, P.S. Walsh, D.F. Plusquellic, T.S. Zwier, J. Chem. Phys. 138 (2013) 204313]. The so determined geometry changes are compared to the results of ab initio spin-component-scaled approximate coupled cluster singles and doubles (SCS-CC2) calculations. [ABSTRACT FROM AUTHOR]

• The rotationally resolved electronic spectrum of 6-methylindole was measured in a molecular beam. • Molecular parameters have been determined from a fit to an asymmetric rotor Hamiltonian using evolutionary strategies. • The transition dipole moment points away from the pyrrolic NH group, indicating the lowest excited singlet state to be L b. • The permanent dipole moment drops slightly from 1.84 D to 1.74 D upon electronic excitation. The rotationally resolved electronic spectrum of the S 1 ← S 0 electronic origin band of 6-methylindole (6-MI) has been measured in a molecular beam and has been fit to rigid asymmetric rotor Hamiltonians in both electronic states using evolutionary strategies. Rotational constants, dipole moments in both electronic states, and orientation of the transition dipole moment in the inertial frame of the molecule have been determined and compared to the results of ab initio calculations. Both the values of the permanent dipole moments as of the transition dipole moment point to an L b -state as lowest electronically excited state in 6-MI. [ABSTRACT FROM AUTHOR]

• Geometry changes of 1-(phenylethynyl)naphthalene upon electronic excitation were determined from fits of fluorescence emission spectra. • The lowest energy feature in the excitation spectrum is assigned to the L b -state. • The geometry changes are compared to the results of ab initio calculations at the approximate coupled cluster singles and doubles (CC2) level of theory. • L a and L b excited states of 1-PEN are energetically nearly degenerate. [Display omitted] The structural changes of 1-(Phenylethynyl)naphthalene (1-PEN) upon excitation from the ground state to the lowest excited singlet state have been assessed from a combined Franck–Condon-Fit of fluorescence emission spectra after excitation of several vibronic bands of 1-PEN and ab initio calculations. An analysis of the infrared spectrum, the laser induced fluorescence (LIF) spectrum and the fluorescence emission spectra is given on the basis of the approximate coupled cluster singles and doubles model (CC2) within the resolution-of-identity approximation and taking spin-component scaling into account. The excited state structure of 1-PEN is found to be planar, with the major geometry changes upon excitation localized in the naphthalene moiety. Electron density shifts from the naphthyl ring to the phenyl ring upon electronic excitation, leading to an increase of the permanent dipole moment of 1-PEN. The lowest electronically excited state of 1-PEN can be labeled as 1 L b -state, with the 1 L a -state energetically quasi-degenerate. The geometry changes, determined from the Franck–Condon analysis are in agreement with this assignment. [ABSTRACT FROM AUTHOR]

• An analysis of the excited state structure of two conformers of 1,3-dimethoxybenzene has been given on the basis of a combined Franck-Condon/rotational constant changes analysis. • The geometry changes are compared to the results of ab initio calculations at the approximate coupled cluster singles and doubles (CC2) level of theory. • The influence of the lone pair orientation of the methoxy oxygen atoms on the electron density differences between both states is surprisingly large. The geometry changes of two rotamers of 1,3-dimethoxybenzene were determined from a combined fit of line intensities in fluorescence emission spectra, obtained via pumping different vibronic transition and the changes of rotational constants upon electronic excitation. The so determined changes are compared to the results of ab initio approximate coupled cluster singles and doubles (CC2) calculations. The bond length variations in the aromatic ring follow the calculated electron density differences from the coupled cluster wavefunctions and are in agreement with excitation to an 1 L b -state for the C 2 v symmetric B-conformer. [ABSTRACT FROM AUTHOR]

• An analysis of the excited state structure of 4-Cyanoindole has been given on the basis of a Franck-Condon-analysis. • The results are compared to ab initio calculations. • The structural changes are typical for an excitation to a La-state. • Additional the information of Mayer and Wiberg bond order analysis and of NBO analysis is given an compared to the experimental geometry changes. The changes of the structure of 4-cyanoindole upon electronic excitation have been determined from a combined Franck-Condon and rotational constants fit. The geometry changes were fit to simultaneously reproduce the intensities of 72 lines in the fluorescence emission spectra, obtained via excitation of six different vibronic bands in the first excited singlet state, along with the three rotational constants from rotationally resolved electronic spectra. [ABSTRACT FROM AUTHOR]

The altered electron distribution after electronic excitation gives rise to structural changes of the heavy atom frame of aromatic molecules. These changes can be influenced by the nature of substituents as well as by their relative position in the aromatic ring. We determined the changes of the structure of 1,2-dimethoxybenzene upon electronic excitation to the first excited singlet state, using a fit of line intensities from the fluorescence emission spectra obtained through various vibronic bands and the rotational constant changes upon excitation from rotationally resolved electronic spectroscopy. The structure fit showed that the benzene ring expands unsymmetrically upon excitation. Clearly, the ring expansion can to some extent be described as ortho -quinoidal. Additionally, a vibrational analysis of the fluorescence emission spectrum based on comparison to an ab initio normal mode analysis at the coupled cluster second order perturbation SCS-CC2/cc-pVTZ level of theory is presented. • An analysis of the excited state structure of 1,2-dimethoxybenzene has been given on the basis of a Franck-Condon-analysis. • Additional the information from the inertial parameters of two isotopologues have been used. • The structural changes can best be described as ortho -quinoidal distortion. [ABSTRACT FROM AUTHOR]