Dimer and excimer states of a conjugated polymer poly(9,9-di-n-octylfluorenyl-2,7-diyl) in thin films

Abstract

Thin films of a conducting polymer, poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) were prepared. PFO was dissolved in tetrahydrofuran (THF) with different concentrations to achieve thin films with different thicknesses. The solution was deposited by spin coating technique on glass substrates. The absorption spectrum has shown two distinguished peaks at 393 (very broad) and 440 nm (sharp). The spectral and amplified spontaneous emission (ASE) properties of PFO thin films were recorded. The photoluminescence (PL) spectra showed two clear peaks and a hump at 428, at 450 and 477 nm, respectively. For higher thicknesses, the PL spectra showed a new hump at 510 nm was observed. The peaks at 428, 450 could be attributed to PFO molecule, whereas, 477 and 510 nm are ascribed to dimer, and excimer, respectively. Under suitable thickness and pump power excitation of Nd: YAG laser (355 nm) the amplified spontaneous emission spectrum was obtained at 512 nm. To the best our knowledge this perhaps is the first report on conjugated polymer PFO in solid state thin film producing ASE from the excimer state.