Side Chain Disorder and Phase Transitions in Alkyl-Substituted, Conjugated Oligomers. Relation to Side-Chain Melting in P3ATs

Abstract

Certain 4,4'-alkyl substituted 2,2'-bithiazole and bithiazole-thiophene oligomers display an endothermic transition in their DSC trace below their respective melting points. Variable-temperature FTIR, MAS-1H NMR, UV-vis spectra, and XRD all indicate that the thermal transition is due to a crystal-crystal phase transition that we have labeled alpha --> beta. FTIR shows a stepwise increase in the concentration of gauche defects at the alpha --> beta transition temperature, but MAS NMR spectra show little increase in the side chain motion until the mp is reached. UV-vis spectra demonstrate that the conjugated main chains remain essentially planar through the alpha --> beta transition, and significant deviations from planarity occur only at higher temperatures, but well below the mp. The close similarity of this behavior to the phase transitions in long chain n-paraffins and the "side-chain melting" phenomenon in poly(3-alkylthiophenes), P3ATs, suggests that the latter may actually be more accurately described as a crystal-crystal phase transition of the crystalline fraction, driven by side chain disorder.

Precipitation and sol formation from poly(p-phenylene)s solutions by spectroscopic study

“…To further study the polymer conformation changes, FT-IR spectroscopy was used to discern the structural information from vibrational resonances of different functional groups. A polymer film was cast from the polymer solution onto a KBr disk, which was then immersed in the solvent vapor atmosphere and dried before FT-IR measurements [28,31]. Similar patterns with slight differences in conformations were observed in the spectra of PP8P films cast from the different solvents, as shown in Fig.…”

“…In order to get more information on the solvent-induced phase separation, the FT-IR spectroscopy experiments [28,31,33] on the polymeric films deposited on KBr disks were also performed. The spectra of PP8P from the different mixed solutions were presented in Fig.…”

Intramolecular CH/π interactions in alkylaromatics: Monomer conformations for poly(3‐alkylthiophene) atomistic models

“…The results presented can influence many aspects of our understanding of thiophene‐based materials. In particular, the existence of accessible conformations other than the linear all‐anti one can affect estimates of the intramolecular and intermolecular components of the internal energy in crystals, side chain disorder and side chain melting, dynamical behavior and charge transport phenomena, thermal behavior and phase transitions, as well as the choice of the most appropriate molecular modeling approach (including force field parameterization) for substituted aromatics. Work is in progress in our group to explore some of these issues through structural and modeling studies of 3‐alkylthiophene oligomers and polymers.…”

Compatibility of PTET‐60/CA blends and separation performance of their membranes for benzene/cyclohexane mixture by pervaporation

“…Consequently, copolymers and co‐oligomers of thiophene and thiazole are considered to have an intramolecular charge‐transferred (CT) electronic state, and such copolymers and co‐oligomers have attracted recent interest 4–13. For example, the synthesis of the type of copolymers and co‐oligomers shown below via organometallic routes has been reported 4–7. The electrochemical synthesis of analogous copolymers has also been reported 14, 15…”

“…Copolymers and co‐oligomers behave as active materials in field‐effect transistors (FETs) 5–7. Recently, it has been reported that copolymers of bithiophene and dialkyl‐bithiazole show a strong tendency to self‐assemble and to form a well‐packed solid structure 9–13.…”