Charge transfer dynamics of copolymer of alkylated oligothiophene with polyethylene oxide (OPTO)^[1] were studied by steady state, femtosecond time-resolved fluorescence  spectroscopy and cyclic voltammetry in the presence of [6,6]-phenyl-C61 butyric acid methyl ester (PCBM). The interaction of polythiophene with PCBM is of great interest due to its possible application as cheap organic photovoltaic cell.

The steady-state spectra of OPTO/PCBM in toluene solution revealed decrease of fluorescence intensity from 3x10⁵ to 10⁴ cps and red shift of Stokes shift from 3007  to 3321 cm^-1 for increasing concentration of the PCBM from 3x10^-8 to 1.3x10^-7 M, respectively. This changes indicates charge transfer between OPTO and PCBM. Time-resolved spectra of OPTO with and without addition of PCBM in toluene solution for wavelength from 440 to 600 nm were observed. The charge transfer process occurred faster at a lower excited state and with more PCBM.

Electrochemical results seem to corroborate the increase of charge transfer when PCBM is add to OPTO once the voltammetric results, obtained at modified screen printed electrode surface, show an increase of peak current for the [Fe(CN)₆]^3-/[Fe(CN)₆]^4- redox probe.

We would like to thank Scientific Cooperation Agreement between Portugal and Slovakia, under the project SK-PT-0015-12, for financial support. This work was also supported by the Ministry of education in the Slovak Republic with grant no. UK/380/20014 and grants: ERDF OP R&D, Project ‘meta-QUTE-Centrum excelentnosti kvantových technológií’, NanoNet2. Inês Miranda is grateful to FCT for financial support under PhD scholarship SFRH/BD/75026/2010.

[1] G. Čík et al. / Synthetic Metals 149 (2005) 31–38.