We did a generalization assuming the fluorescence band in a floating layer on water subphase to be caused by exciplex formation (in pseudo-gaseous and liquid-expanded state). We also showed limits of this generallization. System only remains similar to antisolvent system until compression reaches certain limit. Existence of liquid-expanded state of such an aggregation-labile molecule thus mainly possible due to competition between dye-water and homomolecular dye-dye diffusion interactions. Only at the point of compression isotherm where molecules are pushed beyond critical interaction range, aggregation takes place and excimer formation becomes predominant process. This equilibrium is also the reason why aggregation happens almost instantly, and why the Young modulus drops to negative values. Pressure overshoot is caused by lack of time for structural relaxation. Layer compressibility overcomes zero upon further compression at the point where size reaches that of a flat rectangle of a bottom edge of BODIPY-C18 ≈80 Å2 .