Temperature-dependent intermolecular coupling and exciton migration in an anthracene containing PPE-PPV copolymer

• Photoluminescence (PL) measurements of a statistical copolymer poly-(p-arylene ethynylene)-alt-poly (p-arylene-vinylene)s (AnE-PVstat) thin film within a temperature range between 10 and 300 K.
• A modified Franck Condon (FC) progression with variable 0-0 peak intensity is used to reproduce the experimental PL spectra.
• From the fit, we have determined the variation of the scaling factor αα(related to the amplitude of the 0-0 transition peak), the electronic transition energy E0E0and the disorder parameter σσ with temperature.
• Comparison between theoretical and experimental dependence of the spectral shiftΔε(T)Δε(T)normalized toσ(T)σ(T)versus kTσ(T)used to indicate that two processes promotes the spectral diffusion in AnE-PVstat.
• Dependence of the diffusion length LDLD on temperature and disorder parameterσσ, via the intermolecular separation distance d between excitonic sites involved in a thermally activated hopping.

The dependence upon the temperature of the photophysics of a statistical copolymer anthracene containing poly-(p-aryleneethynylene)-alt-poly (p-arylene-vinylene)s (AnE-PVstat) as a thin film has been investigated. For this purpose, photoluminescence (PL) spectra have been recorded in a temperature ranging between 10 and 300 K. A modified Franck-Condon model has been invoked to analyze the PL spectra. Our findings point out that upon increasing temperature several vibrational modes are activated starting from a transition temperature leading to molecular rearrangements which leads in turn to a decreased intermolecular distance. The latter fact is consistent with the exciton dynamics which has been found to be governed only by a prompt downhill migration to the exciton band edge at low temperatures up to a transition temperature above which a thermally activated hopping process takes place after the downhill migration.