Triple amplified spontaneous emissions from a conjugated copolymer BEHP-co-MEH-PPV in solution

• The spectral properties of BEHP-co-MEH-PPV under low concentrations were studied.
• The laser from BEHP-co-MEH-PPV was found to be in monomeric state of MEH-PPV segment.
• The spectral properties of BEHP-co-MEH-PPV under high concentrations and high power laser were studied.
• The ASE spectra had shown three peaks attributed to the monomeric state, excimeric state and double excimeric state.

The spectral and laser properties of conjugated polymer {[2-[2′,5′-bis(2″-ethylhexyloxy)phenyl]-1,4-phenylenevinylene]-co-[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene]} (BEHP-co-MEH-PPV) in benzene had been studied and presented in this paper. BEHP-co-MEH-PPV was dissolved in benzene to form solutions of concentrations ranging from 1 mM to 10 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 2.5 mM have shown two peaks at 560 nm and 600 nm, which could be attributed to monomer and excimer of MEH-PPV alone. At higher concentration (5 mM) the band at 560 nm almost disappeared and the band at 600 nm became dominant. At still higher concentration, the longer wavelength side of these spectra, there was a hump at 650 nm. So, this new band around 650 nm could be due to double excimer of MEH-PPV alone. When the laser pump power at 355 nm and concentration of above solution were suitably chosen, we observed amplified spontaneous emission (ASE) at 570 nm, 605 nm and 650 nm. These ASE peaks could arise from the monomer, excimer and double excimer states of MEH-PPV as a segment. To the best of our knowledge this is perhaps the first report on ASE from double excimer of the conjugated copolymer, BEHP-co-MEH-PPV, in liquid solution.