Photophysical

Photophysics is the branch of science that studies the physical processes governing the interaction of light with matter. It focuses on how photons are absorbed to create electronically or vibrationally excited states, how these excited states relax back to lower energy levels, and how energy can be transferred between molecules or to surrounding media. Photophysics emphasizes physical mechanisms and excited-state dynamics rather than chemical change, distinguishing it from photochemistry.

When a molecule absorbs light, an excited electronic state is formed. The subsequent evolution of this state can occur through radiative pathways, such as fluorescence (radiative decay from a singlet excited state to the ground state) and phosphorescence (radiative decay from a triplet state), or through non-radiative pathways, including internal conversion, vibrational relaxation, and intersystem crossing. The rates of these processes determine the fluorescence or phosphorescence lifetimes and the overall quantum yield, defined as the fraction of absorbed photons that result in a given emission or event. The Jablonski diagram is a common schematic used to visualize these processes and their relative energy levels and transitions.

Experimental methods in photophysics include absorption and emission spectroscopy, time-resolved techniques, and pump-probe measurements to study ultrafast dynamics. The field addresses a wide range of systems, from organic dyes and polymers to inorganic complexes, quantum dots, and nanomaterials, and its insights underpin applications in lighting, displays, photovoltaics, bioimaging, and photostability design. Understanding environmental effects such as solvent, temperature, and matrix rigidity is also central to modeling excited-state behavior.