We further study the emission properties of our materials in the solid state to test their suitability as gain media. We prepare thin films of our pyrene materials at concentrations of 5 wt% in an organic host matrix of 4,4′-bis(N-carbazolyl)-1,1′biphenyl (CBP) of 230-250 nm thickness on glass. The dilution in a host is required since pyrenes are known to form excimers, which often lead to undesired quenching effects that impair ASE. We pump our materials with short (5-7 ns, 20 Hz) pulses of increasing energy density Ep and record the emission spectrum perpendicular to the film. When excited at lower pump energy, all four compounds show similar spectral emission features in the film compared to the fluorescence taken in non-polar solvents (cf. Figure , 3, S6 and S7). However, when increasing the pump energy, the emission signal of the PyPhCz and PyFlCz films abruptly increases in intensity and the spectrum collapses into relatively narrow bands with a full width at half maximum (FWHM) of 13.8 and 11.7 nm, respectively (see Figure ). By contrast, PyCz and PyPox do not show this effect (see SI for spectra and plots). This lack in spectral narrowing corresponds with the above determined f and ϕ, which were low for PyCz and PyPox similar molar mass. We attribute the absence of ASE in PyCz and PyPox to the stronger CT character of the excited states.