High power amplified spontaneous emission from an oligomer in solution

The laser action from a conductive oligomer 9,9,9′,9′,9″,9″-hexakis(octyl)-2,7′,2′,7″-trifluorene (HOTF) has been demonstrated in this study. First absorption spectra were studied for HOTF in benzene under a wide range of concentrations. The spectra showed that there was only one peak at 355 nm under a wide range of concentrations indicating the absence of dimerization. The fluorescence spectra for low concentrations showed two peaks, at 390 nm and 410 nm, which could be attributed to the monomer and the excimer. At higher concentrations, the peak at 390 nm almost vanished and the dominant peak was at 410 nm with a hump at 435 nm. Laser action was tested in a transverse pumping configuration where the conducting oligomer was pumped by laser pulses from the third harmonic of an Nd:YAG laser (355 nm). It could be seen that there were two amplified spontaneous emission (ASE) peaks, at 390 and 410 nm. These peaks could be attributed to the monomer and excimer of the HOTF oligomer; but, even after our best efforts, we were not able observe the ASE peak at 435 nm corresponding to the hump in the fluorescence spectra. The power of ASE and the photo-chemical stability were remarkably high. This trend for the oligomer is entirely different from its conjugated polymer counterpart poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO). This is perhaps the first report on ASE from an excimeric state of the conjugated oligomer HOTF in liquid solution.