The increase in the intensity of a spectral band due to substituents or interactions with the molecular environment.
See also: auxochrome, hypochromic effect
Source:
PAC, 1996, 68, 2223. 'Glossary of terms used in photochemistry (IUPAC Recommendations 1996)' on page 2247 (https://doi.org/10.1351/pac199668122223)