Evidence for amplified spontaneous emission from double excimer of conjugated polymer (PDHF) in a liquid solution

The spectral and laser properties of conjugated polymer Poly [9, 9-di-(2′-ethylhexyl) fluorenyl-2, 7-diyl] (PDHF) in benzene had been studied and presented in this paper. PDHF was dissolved in benzene to form solutions of concentrations ranging from 12 μM to 6 mM. The absorption spectra had shown no new band when concentration increased; this indicates no dimer formation in these solutions for all concentrations mentioned above. The fluorescence spectra for the concentration 12 μM have shown two peaks at 415 nm and 435 nm, which could be attributed to monomer and excimer. At the longer wavelength side of these spectra, there was a hump at 465 nm. This hump became dominant at concentration 6.25 mM and the peak at 415 nm almost disappeared. So, this new band around 465 nm could be due to double excimer. When the laser pump power at 355 nm and concentration of above solution were suitably chosen, we observed amplified spontaneous emission (ASE) at 415 nm, 435 nm and 465 nm. These ASE peaks could arise from the monomer, excimer and double excimer states of the macromolecule. To the best of our knowledge this is perhaps the first report on ASE from double excimer of the conjugated polymer, PDHF in liquid solution.