Optical and amplified spontaneous emission from an efficient conducting copolymer (PFO-co-MEH-PPV) in solution

Abstract

Optical properties of a conducting co-polymer of poly [(9,9-dioctyl-2,7-divinylenefluorenylene)-alt-co-{2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene}(PFO-co-MEH-PPV) have been investigated in various solvents and concentrations. The absorption spectra of PFO-co-MEH-PPV in tetrahydrofuran (THF) under a wide range of concentrations showed two bands at 455 and 480nm. The ratio of the optical density between these two bands remained constant. Moreover, there was no new band detected at the end of the spectrum. This indicates the absence of the β-phase formation for all concentrations used. On the other hand, the fluorescence spectra of PFO-co-MEH-PPV, for low concentrations, showed two bands at 505 and 535nm. At higher concentrations (above 500nM), the fluorescence spectra were drastically changed. It can be seen that the band at 505nm totally disappeared and there was only one band at 535nm. The band at 535nm could be due to the excimer state. Under pulsed laser excitation of Nd: YAG laser (λex = 355nm), PFO-co-MEH-PPV produced dual amplified spontaneous emission (ASE) peaks at 515 and 540nm. These ASE peaks could be attributed to the PFO-co-MEH-PPV chromophore and coexistence of two segments (excimer).