The spin signature of charged photoexcitations in carbazolyl substituted polydiacetylene

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Abstract
In this article, photoinduced infrared absorption (PIA-FTIR) and light induced electron spin resonance (LESR) measurements on an asymmetric carbazolyl substituted polydiacetylene (PDA), the poly{1-(N-carbazolyl) penta-1,3-diyn-5-ol} (polyCPDO) are presented. Results from both experimental techniques imply that contrary to other well-known polydiacetylene derivatives, in polyCPDO there exist only long-living, highly localized chargedphotoexcitations with spin 1/2 (g value∼2.0026), indicative for polaronic excitations. PolyCPDO also shows a strong dark ESR signal with the same g value as the LESR signal and with a Curie susceptibility of approximately 10 −3 spins per CPDO monomer unit. This unusually high number of defects may come from intermediates of the polymerization. Furthermore, the photoexcited states of composites from polyCPDO mixed with a special solubilized methano-fullerene [6,6]-Phenyl C 61 –butyric acid methyl ester (PCBM) with excellent acceptor properties are investigated and compared with those of the pristine polymer. No enhancement of PIA-FTIR and LESR signals is found for these composites. It is therefore concluded, that even polyCPDO, which shows charged spin 1/2 photoexcitations, does not exhibit a photoexcitedcharge transfer to fullerenes as observed in other nondegenerate ground state conjugated polymerfullerene composites.