SENSITIVE THERMAL-UNDOPING CHARACTERISTICS OF THE SELF-ACID-DOPED CONJUGATED CONDUCTING POLYMER POLY[2-(3'-THIENYL)ETHANESULFONIC ACID]

The structure and properties of the poly[2-(3'-thienyl)ethanesulfonic acid] (P3TESH) treated at temperatures from 20 to 70 degrees C were in vestigated by thermal analysis, ultraviolet-visible-near-infrared and infrared spectroscopies, electron spin resonance, solid-state C-13 nuc lear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy , and conductivity measurements. P3TESH is susceptible to thermal undo ping at low temperatures (40 degrees C for thin solid film). Upon undo ping, the color of P3TESH changes from the original brownish green to brownish orange. The thermal undoping is irreversible due to a permane nt structure change resulting from the nucleophilic attack of the -CH2 CH2SO3- side chain at carbocations to yield C-O bonding and a coupling of the unpaired electrons in polarons on the main chains. As the soli d film is subjected to undoping, its conductivity changes drastically from 10(-2) to 10(-7) S/cm. The sensitivity of P3TESH's color and cond uctivity changes are high compared to those of other conjugated polyme rs. Such characteristics allow P3TESH to be useful for the permanent r ecording of a temperature increase in the low-temperature range.