J. Shinar et al., UV-EXCITED OPTICALLY DETECTED MAGNETIC-RESONANCE (UV-ODMR) STUDY OF PI-CONJUGATED POLYMERS, Molecular crystals and liquid crystals science and technology. Section A, Molecular crystals and liquid crystals, 256, 1994, pp. 691-696
The photoluminescence (PL) and X-band ODMR of poly(p-phenylenevinylene
) (PPV), poly(p-phenyleneacetylene) (PPA), and polythiophene (PT) deri
vative films excited at 254 less than or equal to lambda(ex), less tha
n or equal to 400 nm is compared to those excited at 488 nm. In PPV an
d PT, but not in PPA, UV excitation yields a strong narrow PL-quenchin
g ODMR in addition to the narrow PL-enhancing polaron resonance. In PP
V and PT, the PL yield and the triplet exciton ODMR weaken at short la
mbda(ex). The nature of the narrow resonance is discussed in relation
to recombination of polarons, which may yield luminescent 1(1)B(u) sin
glet excitons but in any case eliminates them as nonradiative singlet
and triplet exciton quenching centers. The UV-excited PL-quenching res
onance is then discussed in relation to several scenarios, including g
eminate polaron recombination and spin-dependent decay of like-charged
polarons into bipolarons. The behavior of PPA derivatives is suspecte
d to result from structural defects which trap the charged excitations
into polarons.