Structural Modifications to Enhance the Exciton Diffusion in Bilayer Porphyrin Fullerene Thin Films

摘要

The effects of peripheral alkyl groups and thermal annealing on the exciton quenching efficiency in bilayer porphyrin-fullerene thin films has been investigated. The thin film UV-vis absorbance spectra, steady-state fluorescence emission, and thermal properties of three carboalkoxyphenyl porphyrin derivatives have been studied: tetra(4-carbohexoxyphenyl)porphyrin (TCH_4PP), tetra(4-carbo-2-ethylhexoxyphenyl)porphyrin (TCEH_4PP), and tetra(4-carbooctoxyphenyl)-porphyrin (TCO_4PP). The quenching efficiencies of these three derivatives have been calculated from their steady-state emission using pristine spin cast films and films with an evaporated C_(40) bilayer. Structural analyses have been performed using X-ray diffraction (XRD), UV-vis spectroscopy, and thermal properties were studied using differential scanning calorimetry measurements (DSC). Annealing the films caused significant structural changes as was observed in the UV-vis absorbance spectra and XRD diffraction patterns. Prior to thermal annealing, quenching efficiencies are greatest for the TCH_4PP and TCO_4PP (hexyl and octyl derivatives), which is in agreement with previous bulk quenching experiments to calculate exciton diffusion lengths. After annealing, the hexyl derivative (TCH_4PP) showed the lowest bilayer quenching efficiency and indicated evidence of significant molecular rearrangements.