Optical probes of pristine and C60-doped silicon-bridged PT polymer; a novel highly luminescent, low bandgap polymer

Silicon bridged PT polymer (PTSi) is a new soluble polymer with a strong luminescence in the infrared band (0-0 transition at 1.6 eV). We have applied various spectroscopies such as absorption, electroabsorption (EA), photo induced absorption (PA), electromodulated PA (EPA), photoluminescence (PL) and photo induced absorption detected magnetic resonance (PADMR) to pristine and C60- doped PTSi thin films in order to eluvidate the photoexcitation and electronic states this material.. The absorption spectrum consists of three bands, one in the visible with a peak at 2 eV and the others in the UV at 4.5 eV and 6.2 eV respectively. The PL band at 1.6 eV contains also three pronounced phonon replica, each 150 meV apart. An electric field reduces the luminescence due to dissociation of excitons into polarons. The PA spectrum is dominated by a broad PA band peaked at 1.1 eV which is due to triplet-triplet transitions, with a shoulder at 1.7 eV due to polaron pairs; there is also a distinctive band at 0.3 eV due to both, polarons and polaron pairs. Upon doping with C60- the 1.1 eV triplet band loses intensity, whereas the 0.3 eV feature dramatically increases and the typical signature of C60- HOMO to LUMO transition appears at 1.15 eV.