Resonance Raman spectra of c i s (CH)x and (CD)x

Abstract

Resonance Raman spectra are reported for as-grown films of the organic semiconductor polyacetylene containing up to 96% of the cis isomer. Spectra were measured for (CH)x and (CD)x at 77 K at 20 cw excitation wavelengths in the range 458 to 680 nm. Excitation profiles for the principal Raman-active modes [at 910, 1250, and 1540 cm−1 in (CH)x and at 976 and 1470 cm−1 in (CD)x] and their first overtones and combinations are presented. Changes in position and shape of these cis Raman bands with changing excitation wavelengths are also presented. Competing luminescence processes following photoexcitation are examined, as are contrasting resonant features associated with the small fraction of trans isomer in these samples.

High‐pressure Raman and infrared spectroscopy of polyacetylene

“…The effect of optical resonance was previously reported as a function of the laser excitation energy. 12 In the present study, the laser energy was constant and the energy gap was changed by the applied pressure.…”

High‐pressure Raman spectroscopy of nanoparticle polyacetylene in a poly(vinyl‐butyral) matrix

“…The sample pressure was determined by exciting the ruby splinters inside the DAC with the 514 nm excitation source and finding the fluorescence peak of the R 1 emission. By comparing the R 1 fluorescence peak at ambient pressure (0 kbar) of the ruby emission with that at any [22,23] Since samples of NPA/PVB contain both trans-and cisdomains, both types of modes are present in the Raman spectrum. Shown is a typical NPA/PVB Raman spectrum obtained with 514 nm excitation and at ambient pressure (0 kbar) with each band labeled by the corresponding vibration in PA. Only half of the unit cell is shown for the cis-modes.…”

“…The normal mode motions along with their corresponding wavenumbers have been calculated by previous researchers, [22,23] and some of the assignments made are presented in Fig. 1.…”

“…The normal mode displacements for the three A g modes in cis-PA [22] are shown in the lower part of Fig. 1 (only half of the unit cell is illustrated).…”

“…The thickness of the sample film may affect the degree of strain and disorder, [22] and it has been noted that the optical absorption of thin films does not necessarily correspond to that of thicker films. [29] The Raman spectrum from 800 to 1600 cm −1 for both thin and thick samples of 50% trans-NPA/PVB using 514 nm excitation was found to be essentially independent of the sample thickness within the thickness range that we studied.…”