Abstract
Optical properties of a conjugated polymer of poly[9, 9-dioctylfluorenyl-2, 7-diyl] - End capped with 2,5-diphenyl-1,2,4-oxadiazole (PFO-1) have been thoroughly studied in different organic solvents and concentrations .The spectral properties of PFO-1 were compared with the conjugated polymer of poly (9,9-dioctyl fluorenyl-2,7-diyl) (PFO-2) under the same operation conditions. The absorption spectra of PFO-1 in tetrahydrofuran (THF), under different concentrations, exhibited only one broad band at390 nm. This broadband (390 nm) comprises two bands at 380 and 400 nm. At higher concentrations, there was no band detected at the end of the spectrum. Under identical operational conditions, PFO-1 exhibited a new band at 437 nm at the end of the spectrum for some other organic solvents. The new band (437 nm) increases rapidly with increasing the concentration. According to our knowledge, the bands at 390 and 437 nm are attributed to alpha (alpha) and beta (beta) phases, respectively. On the other hand, the fluorescence spectra of PFO-1 in THF, for low concentrations, showed four bands; around422, 445,468 and 505 nm. At higher concentrations, the fluorescence spectra were drastically changed. It can be seen that the bands at 422 and 445 nm were totally disappeared, and there were two bands; one at 468 nm (dominant) and another at 505 nm (shoulder). For benzene and toluene, the band at 505 nm was not detected. Under pulsed laser excitation of Nd: YAG laser (lambda(ex) =355 nm), PFO-1 produced dual amplified spontaneous emission (ASE) peaks at 425 and 445 nm for low and high concentrations.