OPTICALLY DETECTED MAGNETIC-RESONANCE (ODMR) STUDIES OF CONDUCTING POLYMERS - AN OVERVIEW

Recent X-band optically detected magnetic resonance (ODMR) studies of films, solutions, and blends of poly(3-alkylthiophenes) and dialkoxy derivatives of poly(paraphenylenevinylene) and poly(paraphenyleneacetylene) are reviewed and discussed. All films and blends exhibit three similar (but not identical) photoluminescence(PL)-enhancing features: (i) a strong narrow (10-15 G wide) resonance at g = 2.0025 +/- 0.0010; (ii) an approximately 1 kG wide triplet powder pattern around g approximately 2; (iii) a 10-30 G wide peak 30-50 G downfield from hv/(2 x 2.003beta) (at g congruent-to 4.07). The narrow resonance is attributed to intrachain 'distant pair' polaron recombination. Its spectral dependence, which is similar to the PL spectrum, indicates that the polaron levels are close to the band edges. Features (ii) and (iii) are attributed to intrachain triplet polaronic excitons. Their zero-field splitting parameters are consistent with a triplet size comparable to that of the thiophene and phenylene rings. The dependence of the ODMR features on sample history and the role of metastable and stable native defects is also discussed.