Molecular absorption spectroscopy is the spectroscopic measurement of wavelength- or frequency-dependent attenuation of electromagnetic radiation resulting from absorption by molecules undergoing transitions between quantized energy states ^[1]. In ultraviolet and visible molecular absorption spectroscopy, absorption occurs primarily when incident photon energies correspond to allowed transitions between molecular electronic states, particularly transitions associated with chromophoric groups ^[1][2]. The measured spectrum represents absorbance or a related absorption quantity as a function of wavelength, wavenumber, or frequency, thereby describing the spectral distribution and magnitude of molecular absorption ^[1]. Under conditions satisfying the Beer–Lambert relationship, absorbance is related to the concentration of the absorbing molecular species, optical path length, and its molar absorption coefficient ^[1][3]. Within biophysical and biochemical research, biomacromolecular absorption spectra arise from intrinsic or associated chromophores, including electronic structures within proteins, nucleic acids, cofactors, and other molecular constituents ^[2][3]. The concept therefore encompasses the physical absorption process, its spectroscopic measurement, and the molecular spectral features generated by energy-state transitions ^[1][2][3].