|Panzer, F.; Bässler, H.; Lohwasser, R.H.; Thelakkat, M.; Köhler, A.: The Impact of Polydispersity and Molecular Weight on the Order–Disorder Transition in Poly(3-hexylthiophene), Journal of Physical Chemistry Letters, 5(15), 2742–2747 (2014) -- DOI: 10.1021/jz5009938|
Conjugated poly(3-hexylthiophene) (P3HT) chains are known to exist at least in two distinct conformations: a coiled phase and a better ordered aggregated phase. Employing steady state absorption and fluorescence spectroscopy, we measure the course of aggregation of P3HT in tetrahydrofuran (THF) solution within a temperature range of 300 K to 170 K. We show that aggregation is a temperature controlled process, driven by a thermodynamic order–disorder transition. The transition temperature increases with the molecular weight of the chains and can be rationalized in the theory of Sanchez. This implies a smearing out of the phase transition in samples with increasing polydispersity and erodes the signature of a first order phase transition. The detection of a hysteresis when undergoing cooling/heating cycles further substantiates this reasoning.