Photoconversion

Photoconversion refers to a light-induced transformation in which a molecule or material changes its chemical structure and thereby its optical properties, such as absorption and emission spectra. The process can be irreversible, resulting in a stable new form, or reversible, allowing repeated cycling between states.

In biology and bioimaging, photoconvertible fluorescent proteins and dyes change their emission wavelength when illuminated with specific wavelengths. Common photoconvertible fluorescent proteins include Kaede, EosFP, Dendra2, and mEos2. Exposure to violet or blue light converts the green-emitting form into a red-emitting form, enabling selective labeling and tracking of subpopulations or lineages. The mechanism is typically a light-induced chemical modification of the chromophore within the protein, altering conjugation and spectral properties. Applications include super-resolution methods such as PALM and lineage tracing in developmental biology.

In chemistry and materials science, photoconversion describes reversible photochromism or irreversible photoinduced transformations. Photochromic compounds such as spiropyrans or azobenzenes switch between two isomeric forms with distinct colors under light. The transition can be reversed with light of another wavelength or with thermal relaxation. Photoconversion is exploited in smart windows, rewritable data storage, photo-patterning, and optical switches.

Key considerations include quantum yield, fatigue resistance (cycle stability), spectral range, and stability of the converted form under ambient conditions. Characterization methods include spectroscopy, fluorescence imaging, and time-resolved measurements.