Interactions of polarons in poly(3-dodecythiophene) at low temperature

Zero-field cooled-field-cooled (ZFC-FC) technique was used to investigate the effect of low temperature (4.6 K) on the interactions of polarons in weakly FeCl3-doped poly(3-dodecylthiophene (PDDT). It was found that the magnetic properties of the system changed with the length of time system spent at low temperature: the Currie–Weiss paramagnetism gradually changed over to “antiferromagnetism” and ultimately to diamagnetism. This effect is connected with the thermochromic properties of self-organized PDDT in primary (10–15 nm) or secondary (30–50 nm) induced aggregates, in which cooling under the glass transition temperature Tg (∼240 K) causes extension of the effective conjugation length of coplanar polymer chains. Changes in magnetic properties are related to the inter- and intra-chain interactions of polaron states within both the primary and secondary induced aggregates.