Dissipation dynamics of intrachain exciton coupled with phonons in MEH‐PPV: Time‐resolved multiplex coherent anti‐Stokes Raman scattering

Abstract

Time‐resolved coherent anti‐Stokes Raman spectroscopy can disentangle the exciton energy dissipation (EED) dynamics of the intrachain exciton in conjugated polymers (MEH‐PPV) coupled with several phonon modes and the corresponding phonon relaxation dynamics by adjusting the timing between lasers in the coherent anti‐Stokes Raman spectroscopy system. The intrachain EED process is coupled with phonon modes located at 966; 1118; 1283; and 1560 cm−1, respectively. Of these, the phonon mode at 966 cm−1 corresponds to the out‐of‐plane CH bending vibration in the vinylene group. This is the primary channel for EED because the vinylene group is close to the conjugated unit and the corresponding chemical bond is flexible. After annihilation of the intrachain exciton, some excess energy from MEH‐PPV in the ground state would further dissipate via energy redistribution between phonon modes at 1283 and 1118 cm−1, ultimately leading to phonon relaxation.

In Situ Surface-Enhanced Raman Spectroscopy on Organic Mixed Ionic-Electronic Conductors: Tracking Dynamic Doping in Light-Emitting Electrochemical Cells

“…This similarity indicates our ability to track the doping profile of MEH-PPV within the LEC device. The strong band at 1580 cm –1 corresponds to the symmetric CC stretching vibration of the phenyl ring, − while two adjacent weaker bands at 1621 and 1554 cm –1 are attributed to the asymmetric CC stretching of vinylene and the CC stretching on the phenyl, respectively. ,, The two bands observed at 1307 and 1283 cm –1 are associated with the asymmetric CC stretching and CC interring stretching coupled with CC–H bending of the phenyl ring, respectively. ,,, It is worth noting that a weaker peak linked to vinylene CC–H bending might be expected around 1330 cm –1 , but it could be overshadowed by a neighboring strong band. , The results also reveal a weak peak around 1180 cm –1 , attributed to CC–H ring bending, and a band at 1108 cm –1 , which emerges from the mixing of C–C stretching and C–H in-plane-bending vibrations within the phenyl group. − The band at 963 cm –1 is attributed to the out-of-plane CH bending of the vinylene group. This particular vibration arises from the dihedral angle between two monomer units, which is forbidden in the Raman spectrum of planar polymer configuration. , …”

“… 54 , 58 , 59 The two bands observed at 1307 and 1283 cm –1 are associated with the asymmetric CC stretching and CC interring stretching coupled with CC–H bending of the phenyl ring, respectively. 54 , 56 , 57 , 60 It is worth noting that a weaker peak linked to vinylene CC–H bending might be expected around 1330 cm –1 , but it could be overshadowed by a neighboring strong band. 61 , 62 The results also reveal a weak peak around 1180 cm –1 , attributed to CC–H ring bending, and a band at 1108 cm –1 , which emerges from the mixing of C–C stretching and C–H in-plane-bending vibrations within the phenyl group.…”

Recent advances in linear and nonlinear Raman spectroscopy. Part XIV

“…Wang et al [ 114 ] used time‐resolved multiplex CARS to study dissipation dynamics of intrachain exciton coupled with phonons. After annihilation of the intrachain exciton, some excess polymer energy in the ground state would further dissipate via energy redistribution between phonon modes, ultimately leading to phonon relaxation.…”