Hard to understand what you mean. A molecule that is fluorescent has excitation max and emission max, but they're not calculated, they're known for a particular compound. Do you need help finding that information out? A fair way to scout this sort of thing out would be to use the compound's UV/Vis max absorbance as excitation, and then scan with the instrument for longer (more to the red, hence less energy) emission, to find the emission max. But that isn't as easy as I've described. You'll have to be far enough away to avoid the instrument's inefficient scatter signal, the molecules' own Rayleigh scattering, and the compound's Raman scattering, which are all false signals. With a fluorometer that can accept the sample in a cuvette, you can build a spectrum and experiment to avoid those signal types, and look for other emission maxima that might be better. But its not as easy with just an HPLC fluorescence detector.