High power amplified spontaneous emission from an oligomer in solution

Abstract

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 355nm under a wide range of concentrations indicating the absence of dimerization. The fluorescence spectra for low concentrations showed two peaks, at 390nm and 410nm, which could be attributed to the monomer and the excimer. At higher concentrations, the peak at 390nm almost vanished and the dominant peak was at 410nm with a hump at 435nm. 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 (355nm). It could be seen that there were two amplified spontaneous emission (ASE) peaks, at 390 and 410nm. 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 435nm 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.