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UV spectroscopy or UV–visible spectrophotometry (UV–Vis or UV/Vis) refers to absorption spectroscopy or reflectance spectroscopy in part of the ultraviolet and the full, adjacent visible regions of the electromagnetic spectrum. Being relatively inexpensive and easily implemented, this methodology is widely used in diverse applied and fundamental applications. The only requirement is that the sample absorb in the UV-Vis region, i.e. be a chromophore. Absorption spectroscopy is complementary to fluorescence spectroscopy. Parameters of interest, besides the wavelength of measurement, are absorbance (A) or transmittance (%T) or reflectance (%R), and its change with time.
Most molecules and ions absorb energy in the ultraviolet or visible range, i.e., they are chromophores. The absorbed photon excites an electron in the chromophore to higher energy molecular orbitals, giving rise to an excited state.[3] For organic chromophores, four possible types of transitions are assumed: π–π*, n–π*, σ–σ*, and n–σ*. Transition metal complexes are often colored (i.e., absorb visible light) owing to the presence of multiple electronic states associated with incompletely filled d orbitals.
Related: Strengths and limitations of UV-Vis spectroscopy
Ultraviolet-Visible (UV-Vis) spectrophotometry is a technique used to measure the absorption of light across the ultraviolet and visible ranges of the electromagnetic spectrum. When incident light strikes matter, it can be either absorbed, reflected, or transmitted. Absorption of radiation in the UV-Vis range causes atomic excitation, which refers to the transition of molecules from a low-energy ground state to an excited state.
Before an atom can change its excitation state, it must absorb enough radiation for an electron to move to a higher molecular orbital. Smaller bandgaps usually correlate with the absorption of shorter wavelengths of light. The energy required for molecules to undergo this transition is, therefore, electrochemically-specific. A UV-Vis spectrophotometer uses this principle to measure analytes in a sample based on their absorption characteristics.
