shows solution spectra of regioregular P3HT in chloroform for four fractions of
different molecular weight achieved by successive extraction in ethyl acetate,
hexane, dichloromethane, and chloroform. The number-average molecular weight
(M n ) of these fractions was 2.2 kg/mol (PDI ¼ 1.43), 5.6 kg/mol (PDI ¼ 1.18),
13.8 kg/mol (PDI ¼ 1.48), and 19.0 kg/mol (PDI ¼ 1.35). For regioregular P3HT,
increasing the molecular weight leads to a slight bathochromic shift of the absorption maximum in solution, which results from an increase in the average conjugation length along the polymer backbone [17, 30].
Fig. 3 (a) Absorbance
(solid line) and fluorescence
(dotted line) spectra of
regioregular P3HT with
97% HT-HT coupling (top)
and regiorandom P3HT
with 64% HT-HT coupling
(bottom) in chloroform
solution [39]. (b)
Absorbance of regioregular
P3HT in chloroform
solution as a function of
molecular weight. The
fractions were obtained by
successive solvent
extraction in ethyl acetate
(dashed line), hexane
(dotted line),
dichloromethane (dasheddotted line), and chloroform
(solid line) [17]. (Reprinted
with permission from
Adachi
et al. [39]. Copyright (2011)
American Chemical
Society. And reprinted with
permission from Zen
et al. [17]. Copyright (2004)
Wiley-VCH)
46
K. Tremel and S. Ludwigs