The quest for factors controlling the partition of excitation energy between fluorescence and nonradiative processes in tryptophan is of perennial interest to spectroscopists because its fluorescence has distinct intensity, color and environmental sensitivity. Solving the relationship between specifics of molecular environment and characteristics of tryptophan fluorescence would provide the key for emission spectra interpretation of a wide variety of proteins. Our quantum mechanical calculations and molecular modeling reveal substantial differences in ground state isosurface charge distribution on the indole ring for Lys-Trp dipeptides when backbone and residue charge is varied. These isosurfaces represent the superposition of all ground state molecular orbital contributions to charge distribution and thereby provide a visual representation of the contributions of all relevant orbitals. Comparison of Lys-Trp species isosurfaces with experimentally derived quantum yields and fluorescence lifetimes reveals a correlation: high π-electron density on the indole ring is associated with high quantum yield and long average lifetime, both of which are found in the zwitterionic and anionic states. Conversely, low quantum yield and short average lifetime is associated with low, uneven π-electron density on the indole ring, which is found in the cationic and highly anionic state where the indole amine is deprotonated. This interpretation explains fluorescence results for tryptophan-containing proteins. Where x-ray crystal structures have shown proteinaceous tryptophans to be hydrogen bonded at the indole amine, very low quantum yields are observed, and isosurfaces resembling those with a deprotonated indole amine are anticipated. Thus isosurfaces reveal losses in π-electron density over the indole ring or a loss of aromaticity for low fluorescing tryptophans. Isosurfaces are the key to solving the relationship between molecular environment and tryptophan fluorescence.