Effect of concentration of anionic polymethine dye in poly-N-epoxypropylcarbazole polymer film composite on the spectral-luminescent properties and photoconductivity

The absorption, fluorescence and fluorescence excitation spectra of polymer thin film composites based on poly-N-epoxypropylcarbazole (PEPC) doped with different content of anionic polymethine dye testify to the formation of contact ion-pair associates at high concentration of the latter. The photoconductivity of such composites in the visible spectrum region is observed, despite the absence in the polymer of any fragment capable of accepting a photoexcited electron from anionic dye chromophore. Analysis of the spectral data together with DFT/B3LYP quantum-chemical calculation of the HOMO and LUMO energies of the monomer N-methylcarbazole unit and the radical of the polymethine dye allowed us to suggest the possible mechanism of internal photoeffect in the investigated composites which is based on the formation of the contact ion-pair associates.

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► We studied properties of thin films of PEPC doped with the anionic polymethine dye.
► Absorption and fluorescence spectra of composites were measured at 0.1–10% of dye.
► Formation of H-aggregates were revealed at high concentration of the dopant.
► p-Type photoconductivity of PEPC was observed at >5% content of the dopant.
► Mechanism of carriers generation was suggested and verified by DFT calculation.