The redox properties of model chromophores from the greenfluorescentprotein family are characterized computationally using density functionaltheory with a long-range corrected functional, the equation-of-motioncoupled-cluster method, and implicit solvation models. The analysisof electron-donating abilities of the chromophores reveals an intricateinterplay between the size of the chromophore, conjugation, resonancestabilization, presence of heteroatoms, and solvent effects. Our bestestimates of the gas-phase vertical/adiabatic detachment energiesof the deprotonated (i.e., anionic) model red, green, and blue chromophoresare 3.27/3.15, 2.79/2.67, and 2.75/2.35 eV, respectively. Vertical/adiabaticionization energies of the respective protonated (i.e., neutral) speciesare 7.64/7.35, 7.38/7.15, and 7.70/7.32 eV, respectively. The standardreduction potentials (Ered0) of the anionic (Chr•/Chr–) and neutral (Chr+•/Chr)model chromophores in acetonitrile are 0.34/1.40 V (red), 0.22/1.24V (green), and −0.12/1.02 V (blue), suggesting, counterintuitively,that the red chromophore is more difficult to oxidize than the greenand blue ones (in both neutral and deprotonated forms). The respectiveredox potentials in water follow a similar trend but are more positivethan the acetonitrile values. [ABSTRACT FROM AUTHOR]