Phase analysis of vibrational wave packets in the ground and excited states in polydiacetylene

Abstract

Molecular vibration of several modes in blue-phase polydiacetylene-3-butoxycarbonylmethylurethane (PDA-3BCMU) was real-time observed by 5-fs pump-probe measurement. The contribution of the vibrational wave packets in the ground state and in the excited state in the signal were separated by multichannel measurement. The C v C stretching mode in the ground state starts to oscillate -out-of-phase with the C w C stretching mode. The structure of PDA-3BCMU in the geometrically relaxed state is not pure butatriene type but more like acetylene type. The frequencies of C v C and C w C stretching modes there were determined by singular value decomposition method to be 1472± 6 cm −1 and 2092± 6 cm −1 , respectively. The double and triple bond stretching frequencies in the ground state are 1463± 6 cm −1 and 2083± 6 cm −1 , respectively.

Surface-Enhanced Impulsive Coherent Vibrational Spectroscopy

“…The information about the initial vibrational phase allows the vibrations of the ground and excited electronic states to be separated from each other4445. The initial vibrational phase denotes the position where the coherent wave packet motion along the potential energy surface starts for each probe wavelength, which can be extracted from the pump-probe signal by the linear prediction singular value decomposition (LP-SVD) method45.…”

“…The initial vibrational phase denotes the position where the coherent wave packet motion along the potential energy surface starts for each probe wavelength, which can be extracted from the pump-probe signal by the linear prediction singular value decomposition (LP-SVD) method45. If the initial vibrational phase φ is π/2 or 3π/2 (0 or π), the vibrational frequency is due to the wave-packet motion in the ground (excited) state444546. The vibrational phases for all the observed modes are quite complicated.…”

“…Therefore, the former has contributions from both the ground-state and the excited-state wave packets, while the latter has contributions mainly from the excited wave packet. The contribution from the excited-state wave packet is calculated by444546 (cos φ )2, as shown in Fig. 3(b).…”

Ultrafast depolarization of the fluorescence in a conjugated polymer

“…The ultrafast changes in the TA spectra and the dynamics of vibrational wave packets in polydiacetylene have been explained in terms of the geometrical relaxation of a free exciton to a self-trapped state within 100 fs. 40 In addition, ϳ30 fs depolarization component was observed in the stimulated emission signal from amorphous films of polythiophene, 41 which could not be explained by incoherent hopping and may also represent a signature of dynamic localization. All these observations suggest that structural relaxation and dynamic localization phenomena are common in conjugated polymers.…”

Exciton self‐trapping in MEH‐PPV films studied by ultrafast emission depolarization

“…The relaxation energy in the polymer was in fact very similar to that in a PPV pentamer, where delocalization of the primarily exciton is limited by pentamer length. Ultrafast vibrational coherence gives an indication of structural relaxation within 100 fs in another conjugated polymer polydiacetylene [5]. Some information on exciton size (maximal distance between electron and hole) is obtained from polarizabilities, which can be measured by electroabsorption in the Franck-Condon region (before structural relaxation) [6,7] and by GHz and THz conductivity for the relaxed excitons [8,9].…”