Ultrafast dynamics of laser from green conjugated-oligomer in solution

Abstract

In this work, we report on the time resolved spectroscopy of amplified spontaneous emission (ASE) from the conjugated oligomer (CO) 9,10-Bis[(9-ethyl-3-carbazoyl)-vinylenyl]-anthracene (BECVA) only upon energy transfer from another oligomer 1,4-Bis(9-ethyl-3-carbazo-vinylene)-9,9-dihexyl-fluorene (BECV-DHF). BECVA do not dissolve readily in tetrahydrofuran (THF) at room temperature, but completely dissolved when the temperature of the solution (THF & BECVA mix) was risen to 65 °C and remained dissolved even after cooling to room temperature. The process of heating and dissolving do not affect the performance of the CO. The heat-treated solutions were used to perform all experiments, unless mentioned. The absorption spectra indicated no aggregate formation upon increasing concentration, but the fluorescence spectra were very different for several concentrations of the solution, indicating the presence of the excimer. Pure BECVA in THF was pumped at various pump powers and concentrations. This produced only a broadband emission (from 500 to 750 nm) with a FWHM of 250 nm, which has potential applications in white light OLED. Next, we tried to produce ASE using the energy transfer process from a conjugated polymer (CP) poly (9,9-dioctylfluorenyl-2, 7-diyl) (PFO); however, this did not produce ASE, which could be due to the significant hindrance of the macromolecular PFO. The intensity of the BECVA spectra was enhanced with energy transform from PFO. The output was a broadband emission ranging from 400 to 750 nm (FWHM 350 nm). Finally, we added the oligomer BECV-DHF in solution (THF) to the BECVA solution at optimal pump power and concentration of donor (BECV-DHF), and the super-irradiant laser was produced from BECVA at 500 nm with a FWHM of 6 nm. The ultrafast dynamics of the BECVA solution under high pump power excitation and different energy donor (PFO and BECV-DHF) were extensively studied in this work. To the best of our knowledge, this is the first report of a CO that does not intrinsically produce ASE, but produces efficient ASE only via the energy transfer process by another CO.