Chromophore: A moiety of a molecule that may be accountable for selective absorption of radiation in a particular range of specially UV or visible region.

Auxochrome: A chemical cluster which is not going to give rise to an absorption band independently, but upon being attached to a chromophore alters both the position and intensity of the absorption peak.

Bathochromic shift: It is a shift of the peak position (lmJ to a higher wavelength due to the effect of a substituent group or solvent, it is also known as x red shift.