Improved synthetic methodology for poly(3-hexyl- and 3-octyloxycarbonylthiophene-2,5-diyl) (
1a and
1b) is reported.
n
=6700 and 9400 (
w
/
n
=2.5 and 3.2),
λ
max
for fluorescence emission=600 and 610 nm and
λ
max
for electroluminescence=600 and 615 nm, for
1a and
1b respectively. The
1
H NMR spectra required that pentads be considered to explain the spectra. That is the four nearest neighbours to a given ring influence the
1
H NMR spectrum. Electroluminescence efficiencies of 0.016% and 0.018% were observed for devices made from
1a and
1b, respectively. A bilayer device of ITO/poly(3-octylthiophene)/
1b/Al emitted at 646 nm, the same wavelength where poly(3-octylthiophene) itself emits. The efficiency was low but was an order of magnitude greater than for poly(3-octylthiophene) itself. Regioregular (HH-TT) poly(4,4′-bis(hexyl- and octyloxycarbonyl)[2,2′-bithiophene]-5,5′-diyl) (
3a and
3b) were also prepared
via the Ullmann reaction and
n
=7900 and 11000 respectively. Films of
3a and
3b were yellow in color and showed
λ
max
=377 and 381 nm respectively, about 55-80 nm blue shifted compared with
1a and
1b. This is due to the large rotational barrier in the HH dyads which reduces the effective conjugation length in
3a and
3b.
3a and
3b showed bright fluorescence and electroluminescence with emission of yellow light. Electroluminescence efficiencies were 8.5×10
–3
% and 4.7×10
–3
%, respectively.