Effect of Molecular Weight on Spectroscopic and Spectroelectrochemical Properties of Regioregular Poly(3-hexylthiophene)

Abstract

Using experimentally established sequence of extractions, we were able to fractionate regioregular poly(3-hexylthiophene) (R-P3HT) into four fractions differing significantly in their molecular weight (Mn) and exhibiting low polydispersity coefficients. 1H NMR analysis of low molecular fractions enabled us to propose the dominant chain termination mechanisms and identify the sources of regioregularity defects. In particular, it turned out that the presence of small amounts of undesired isomer of 2-bromo-3-hexylthiophene, namely, 2-bromo-4-hexylthiophene, strongly influences the molecular weight and to a much lesser extent the regioregularity of the polymer obtained via Grignard type polycondensation. In the reaction with the growing chain, 2-bromo-4-hexylthiophene either causes its termination, lowering in this manner the molecular weight of the resulting polymer, or introduces regioregularity defects of TT-HH (TT = tail to tail; HH = head to head) type. The average conjugation length in R-P3HT increases with the increase of Mn as manifested by a bathochromic shift of the lambdamax and the appearance of the vibrational structure in the UV-vis-near-IR spectra of the fractions of higher molecular weight. This conclusion is supported by FTIR data. The onset of the oxidative doping of R-P3HT shifts to lower potentials with the increase of the molecular weight as evidenced by cyclic voltammetry and UV-vis-near-IR spectroelectrochemistry.

Microscopic and Spectroscopic Investigation of Poly(3-hexylthiophene) Interaction with Carbon Nanotubes

“…A downshift up to 40 meV or 8 nm is observed for the spectra maximum as the content of DWNTs is raised. This phenomenon has been previously observed and associated with an increase of the conjugation length of the polymer [28,30]. We can therefore conclude that the strong interaction between the two materials is the driving force leading to an increased organization of the polymer chains on the nanotube surface, as already assessed by microscopy studies.…”

“…Pristine P3HT spectrum is characterized by a maximum labeled "C" at 2.42 eV corresponding to 0-2 optical transition [28]. Two other features labeled A and B in the graph occur at 2.02 eV and 2.19 eV respectively points extracted with a second derivative analysis.…”

Williamson ether synthesis: an efficient one-step route for surface modifications of silicon nanoparticles

“…[36] The photoluminescence spectra shown in Figure 4 are in good agreement with previously published photoluminescence spectra for alkyl-functionalised silicon nanoparticles, which show a strong blue luminescence for small silicon nanoparticles of sizes up to 5 nm as synthesised by specific techniques. [37][38][39][40] It should be noted, however, that the origin of blue luminescence in functionalised silicon nanoparticles is still the subject of debate and is dependent upon the specific method of formation.…”

Unexpectedly high field-effect mobility of a soluble, low molecular weight oligoquaterthiophene fraction with low polydispersity

“…The herein investigated PQT-12 fractions have been generated by the solvent extraction method as extensively described for regioregular poly(3-hexylthiophene), P3HT [6,13]. The solvents used as well as the molecular weights and the parts by weight of the resulting PQT-12 fractions are listed in Table S2 in the ESM.…”