Polarized fluorescence in α-sexithienyl single crystal at 4.2 K

Abstract

The polarized fluorescence spectra of the bc plane of α-sexithienyl (αT6) single crystal at T=4.2 K have been measured and analyzed. The spectra show a sharp component superimposed on a broad component. The origin of fluorescence at 18332 cm−1 with a rather narrow linewidth (FWHM=8 cm−1) is completely polarized along b. We assign it to a shallow X-trap 18 cm−1 below the bottom of the 1 1Bu exciton band. The 1 1Bu molecular electronic excited level splits in the crystal in four Davydov components (ag, bg, au, and bu) of which au and bu are dipole allowed. The calculated exciton band structure based on the Ewald sums, assuming the point dipole–dipole approximation, predicts two lowest degenerate Davydov components: an au b polarized component and a forbidden ag component. The fluorescence with the intrinsic sharp vibronic progressions is analyzed in terms of ground state totally symmetric modes which are in excellent agreement with Raman scattering data of the single crystal. Sharp c polarized false origins are identified at 18 167, 18 084, and 18 026 cm−1 and discussed either in terms of X-traps or Herzberg–Teller vibronic coupling with the second higher 2 1Bu molecular level polarized along the in plane short axis. A broad c polarized component is attributed to aggregates.

Confocal Raman Spectroscopy of α‐Sexithiophene: From Bulk Crystals to Field‐Effect Transistors

“…Raman spectra were measured with a Jobin Yvon T64000 triple monochromator, spanning the region 10-2000 cm -1 , with particular attention to the low frequency region of the lattice phonons (10-150 cm -1 ). The excitation wavelength was from a Kr laser tuned at 647.1 nm, whose energy is sufficiently low to avoid fluorescence, either exciton-like or from impurities [30][31][32]. The laser power focused on the sample was reduced with a neutral filter, whose optical density was selected in each experiment to prevent crystal damage, the actual power being in most cases below 1 mW.…”

Spider‐Like Oligothiophenes

“…This conjugation improvement is significantly higher than the expected one considering oligomers in solution ( Figure 1b and c); this points to a solid-state effect, possibly connected with pstack interactions between adjacent molecules at short interchain distances in the conducting film. [25] Table 5. UV characterization of the electrosynthesized conducting films .…”

Morphology Controlled Energy Transfer in Conjugated Molecular Thin Films

“…The nature of the optical emission from an ordered a-sexithienyl single crystal is excitonic with the 0±0 electronic origin located at 18 360 cm ±1 . [14] A number of vibrational modes are effectively coupled to the electronic origin, the most intense of which is the C=C double bond stretching vibration at 1460 cm ±1 . Therefore, the fingerprint of ordered excitonic emission is the energetic position of the electronic origin, and the well-resolved vibrational fine-structure with the dominant vibronic peak at 16 900 cm ±1 .…”