The modification of molecular properties by the use of substituents is a versatile route for molecular design. Here we show for the example of multiresponsive spiropyrans that substituent effects and their correlations can be accurately described by Hammett constants, which in turn can be obtained directly from density functional theory calculations. The internal energetic difference Delta U between the noncolored and the colored form is determined for 63 spiropyran derivatives with substituents at the spiropyran N-and C-6-positions, and:can be described by only five parameters with an accuracy better than, 0.1 eV (9.75 kJ/mol) using Hammett constants. This enables the prediction of Delta U values for other substituents without the need for further calculations nor experiments.