Photophysics of PPV derivatives with varying conjugation lengths

Photoluminescence (PL), electroluminescence (EL) and photoconductivity (PC) of poly[(2,5-dimethoxy-p-phenylene) vinylene] (DMPPV) of varying conjugation length were studied. Thin film devices of the DMPPV with different conjugation lengths, as the active medium, were prepared. The PL emission spectra revealed the radiative decay of the singlet excitons with peak values corresponding to energies below the absorption onset. The PL emission spectra of the copolymer films also revealed vibronic features, which get well resolved upon cooling to 80K. The devices exhibit light emitting diode (LED) behavior; the I–V curves and EL spectra are compared in these DMPPV samples having different conjugation lengths. The PC studies reveal subtle features, which can be attributed to the optically generated excitations in the system.