Single-crystal reflection and Raman spectra of the polydiacetylene THD

Exciton spectroscopy of red polydiacetylene chains in single crystals

“…Table 1: Transition energies of the exciton and its satellites, taken from spectra of Im(ε) derived from the electroreflectance at low temperature. ∆E refers to the energy difference to the exciton and yields the vibrationnal energies in good agreement with Raman modes measured at room temperature [9] and low temperature (this work). Table 1…”

“…For parallel polarization of light, the room temperature spectrum in fig. 1 shows a broad exciton peak of about 30% reflectance followed by a vibrational band as reported earlier [9]. Low temperature reflectance spectra show some narrowing of the main peak, and a manifold of vibronic exciton peaks appears as is typically observed in high-quality polydiacetylene single crystals [15,17].…”

“…The room temperature crystal structure has been determined [8]. Room temperature reflectance and Raman scattering spectra have been measured by Morrow [9]. The Kramers-Kronig transformation of the reflectance yields a zero phonon absorption band peaked at 568 nm and characteristic of a red PDA phase.…”

“…The frequency of the double bond and triple bond stretching modes are respectively 1481 ± 2 cm -1 and 2107 ± 2 cm -1 . For a detailed discussion of the attribution of the other lines see[9].…”

Twisted polydiacetylene quantum wire: Influence of conformation on excitons in polymeric quasi-one-dimensional systems

“…A possible explanation for this discrepancy has been proposed in [17]. A recent DFT theoretical calculation [26] indeed relates a stable non planar chain conformation to the spectroscopic properties (visible absorption, vibrational frequencies, NMR chemical shifts) in a simple model PDA and in the known PDA poly-THD [27,28,29,30]. The presence of low energy dark states has been related theoretically to the importance of electronic correlations, as was claimed before for polyenes [31,32].…”