OPTICALLY DETECTED MAGNETIC-RESONANCE (ODMR) STUDY OF POLY(3-HEXYLTHIOPHENEACETYLENE (P3HTA) FILMS

The photoluminescence (PL) and X-band ODMR of poly(3-hexylthiopheneacetylene) (P3HTA) films is described and discussed, As in poly(3-alkylthiophenes) (P3ATs), poly(p-phenylenevinylenes) (PPVs), poly(p-phenyleneacetylenes) (PPAs), and their derivatives, three PL-enhancing ODMR features are observed. The strongest is a narrow asymmetric (DELTAH-1/2 is similar to 14 G) line which is the sum of a broad Gaussian at g almost-equal-to 2.0032 +/- 0.0007 and a narrow Gaussian at g almost-equal-to 2.0022 +/- 0.0007. This asymmetry is slightly weaker than that found in P3ATs, but much stronger than in PPVs and PPAs. Since the resonance is attributed to polaron-polaron fusion into nongeminate singlet excitons, the lineshape thus indicates that P3HTA is more charge conjugation symmetric than P3ATs but less than PPVs and PPAs. The other two features are a broad full-field and a narrower half-field triplet powder pattern, attributed singlet exciton generation via triplet-triplet exciton fusion. However, while the half-field resonance of P3ATs, PPVs, and PPAs displays a single line, that of P3HTA is clearly resolved into two peaks. The nature of these observations is discussed in relation to disorder effects.