Regioregular poly(4,4'-didecyl-2,2'-bithiophene) with exclusively head
-to-head and tail-to-tail couplings between adjacent alkylated thiophe
ne rings was studied as a potential material for the active layer in l
ight-emitting diodes (LEDs). Readily visible green light was derived f
rom a single layer LED structure, The electroluminescence (EL) spectru
m peaks at 2.2 eV, Excitation of photoluminescence (PL) resulted in gr
een light with the spectrum peaked at 2.3 eV. Additionally to the elec
troluminescence and photoluminescence measurements, the absorption spe
ctrum is reported, Determination of the optical energy gap gave E(g) e
qual to 2.9 eV, The same experiments performed for another regioregula
r polyalkylthiophene system (with only head-to-tail couplings) showed
extremely poor EL and PL intensity, below the sensitivity of our spect
rometer, The difference in yield of photo- and electroluminescence is
likely interpreted in terms of trapping of excitons in conjugated bloc
ks separated by head-to-head dyads, where they decay. Non-planarity of
the polymer backbone also influences the relative positions of single
t and triplet states.