Polaron dynamics in two types of long oligothiophenes revealed byQ- andX-band ESR measurements

Abstract

The polaron dynamics has been investigated through the X-and Q-band ESR measurements for two types of iodine-doped long oligothiophenes, the 20-mer with octyl substituents ͑o-20T͒ and the 16-mer with hexyl substituents ͑h-16T͒. o-20T, used as a model compound of conjugated polymers with crystalline grains, gives anisotropic ESR spectra attributed to g anisotropy at low temperatures. The anisotropic spectra are found to be brought by polarons moving within the crystalline grains consisting of parallel chains. The anisotropy is shown to decrease with increasing temperature. This provides definite evidence that the polarons transfer among some grains by the assist of temperature. In contrast, h-16T, used as a model of the polymers with amorphous morphology, gives almost isotropic ESR spectra even in the Q-band measurement. This feature of h-16T is explained to be caused by a rapid interchain transfer of polarons. Spectral simulations performed for obtained spectra reveal that the ESR linewidth in the Q-band measurement is larger than that in the X band for both oligothiophenes. The difference of the linewidth is analyzed by a simplified motional narrowing model in order to draw the information of polaron dynamics. Analyses for o-20T show that the intergrain motion almost follows the variable range hopping model. The interchain motion in h-16T is found to have a much weaker temperature dependence than the intergrain motion in o-20T. This result suggests that the interchain dynamics of h-16T revealed by the ESR technique includes a variety of processes of motion.

Electron–Hole Pairs Generated in the Crystalline Phase of Polymer Diodes Studied by Electrically Detected Magnetic Resonance Techniques

“…P3HT is known to form a solid film with microcrystalline lamellar structures because of strong interchain coupling, and the peak energy of the bleaching signal observed in the BM measurements indicates the formation of such a lamellar structure. ,, The carriers in the P3HT diode are, thus, expected to be delocalized across several chains in the lamellae . Hole carriers delocalized over several polymer chains of polythiophene derivatives have been previously reported to tend to exhibit a center g -value lower than g e , whereas hole carriers localized in a single chain have been reported to exhibit a center g -value greater than g e . The g -value of holes determined in Figure was smaller than g e , suggesting actually the formation of the holes delocalized over several chains.…”

Self-assembled cyclic oligothiophene nanotubes: Electronic properties from a dispersion-corrected hybrid functional

“…1 Because of their high carrier mobilities, oligo-and polythiophenes have been utilized in organic field-effect transistors (OFETs), organic light-emitting diodes (OLEDs), and photovoltaic materials. 2,3 Although linear thiophene chains have shown great utility in optoelectronic devices, cyclic organic materials are of considerable interest due to their conserved and symmetrical three-dimensional structures. For example, porphyrin nanotubes are known to self-assemble via strong ionic interactions, 4 and cyclic oligothiophenes have also demonstrated very stable self-assembling properties.…”

Temperature dependence of intra‐chain photoluminescence of a long oligothiophene

“…In this regard, long sized conjugated oligomers with definite chain length are ideal compounds for the research. In reality, the use of such oligomers has been shown to be effective for the research of conjugated polymers [3][4][5][6][7][8][9][10].…”