Femtosecond Time-Resolved Photoluminescence Measurements of PPV, MEH-PPV and CN-PPV

Abstract

Conjugated polymers based on poly(arylenevinylene)s are of potential technological importance due to their electroluminescence properties^1,2. In poly(p-phenylenevinylene) [PPV] and its soluble derivative poly(2-methoxy,5-(2’ethyl-hexyloxy)-p-phenylenevinylene) [MEH-PPV] the luminescence produced after photoexcitation or charge injection is attributed to the radiative recombination of the same singlet excited state, namely the neutral polaron-exciton. Obtaining a detailed understanding of the dynamics of excitons in PPV and its derivatives prior to recombination is therefore highly desirable for both fundamental and practical reasons. The method employed in our experiment was that of time-resolved photoluminescence spectroscopy. Optically thick films of the polymers were excited, under a vacuum of 8x10^-6 mbar, by 200 fs pulses of 3.06 eV photons from the frequency-doubled output from a modelocked Ti:Sapphire laser. The energy of the photons corresponded to the peak of the absorption spectrum for PPV. The luminescence was temporally and spectrally resolved using the upconversion technique³. The overall temporal resolution was about 300 fs and the spectral resolution was 18 meV.