Isolated Building Blocks of Photonic Materials:  High-Resolution Spectroscopy of Excited States of Jet-Cooled Push-Pull Stilbenes

Abstract

The lowest excited singlet states of 4-(dimethylamino)-4′-cyanostilbene (DCS), 4-(dimethylamino)-4′nitrostilbene (DANS), and 4-di(hydroxy-ethyl)amino-4′-nitrostilbene (DANS-diol) have been investigated by high-resolution fluorescence excitation and dispersed emission spectroscopy on samples seeded in supersonic expansions. Using ab initio calculations of the harmonic force fields of the electronic ground state as a starting point for the analysis of vibrational modes and frequencies, detailed vibrational assignments of the rich line structure of the S 1 r S 0 transition in these three push-pull stilbenes are reported. From the experimental and theoretical analysis, it becomes apparent that the excitation spectra are dominated by low-frequency vibrational modes of the stilbene-like backbone, albeit that a characterization in terms of trans-stilbene vibrational terminology is not very appropriate. The fluorescence excitation and emission spectra show significant Franck-Condon factors for transitions involving these vibrational modes, in line with significant geometry changes in the stilbene moiety upon electronic excitation. Comparison of the spectroscopic data of the DANS chromophore in DANS and DANS-diol demonstrates that the inclusion of the diol auxiliary function has a significant effect on its spectroscopic properties. Similarly, the comparison between solution and gas-phase data leads to the conclusion that spectroscopic data obtained in solution for DCS allow for a reasonably good extrapolation to the isolated molecule but that the structure of DANS is, even in low-polarity solvents, already modified to a larger extent than would a priori be expected.

New trans-stilbene derivatives with large two-photon absorption cross-section and non-linear optical susceptibility values – a theoretical investigation

“…It has also been reported in earlier studies that the trend followed by d OPA is not influenced by o 0f . The gas phase o 0f value, 3.27 eV, of TSBD-2 is close to the experimentally reported 47 value 3.69 eV and very close to the earlier theoretically reported 48 value 3.39 eV. The value of m 0f (3.91 a.u.)…”

Excited-state vibrational relaxation and deactivation dynamics of trans-4-(N,N-dimethylamino)-4′-nitrostilbene in nonpolar solvents studied by ultrafast time-resolved broadband fluorescence spectroscopy

“…Although this mode does not associate with a significant structural change according to the DFT calculations at the CAM-B3LYP level of theory, it is modestly active probably because either the S 0 or S 1 state is actually slightly nonplanar. Indeed, this mode has been observed in the gas-phase fluorescence excitation spectrum with a S 1 -state vibrational frequency of 24.6 cm À1 [41]. The coherent bandwidth of our excitation pulse ($150 cm À1 ) is broad enough to coherently excite several vibrational levels of this mode and create a vibrational wave packet along this coordinate.…”

The index of microcirculatory resistance (IMR) in takotsubo cardiomyopathy

“…3), 4‐(dimethylamino)‐4′‐cyanostilbene (DCS) 4‐(dimethylamino)‐4′‐nitrostilbene (DANS). These systems served as benchmarks for many experimental32, 33 and theoretical studies28, 29. The ICT excitation energy for DANS has been found to be reasonably reproduced (gas‐phase experiment) by the CAMB3LYP and CAMPBE0 functionals, underestimating by 0.2 and 0.3 eV, respectively29.…”