A chromophore is the part of a molecule responsible for its color. The color arises when a molecule absorbs certain wavelengths of visible light and transmits or reflects others. The chromophore is a region in the molecule where the energy difference between two different molecular orbitals falls within the range of the visible spectrum. Visible light that hits the chromophore can thus be absorbed by exciting an electron from its ground state into an excited state.

In biological molecules that serve to capture or detect light energy, the chromophore is the moiety that causes a conformational change of the molecule when hit by light.

Chromophores almost always arise in one of two forms: conjugated pi systems (also known as resonating systems) and metal complexes.

In the conjugated chromophores, the electrons jump between energy levels that are extended pi orbitals, created by a series of alternating single and double bonds, often in aromatic systems. Common examples include retinal (used in the eye to detect light), various food colorings, fabric dyes (azo compounds), pH indicators, lycopene, β-carotene, and anthocyanins. Various factors in a chromophore's structure go into determining at what wavelength region in a spectrum the chromophore will absorb. Lengthening or extending a conjugated system with more unsaturated (multiple) bonds in a molecule will tend to shift absorption to longer wavelengths. Woodward-Fieser rules can be used to approximate ultraviolet-visible maximum absorption wavelength in organic compounds with conjugated pi-bond systems.

Freeman John Dyson FRS (born December 15, 1923) is a British-born American theoretical physicist and mathematician, famous for his work in quantum electrodynamics, solid-state physics, astronomy and nuclear engineering. Dyson is a member of the Board of Sponsors of the Bulletin of the Atomic Scientists. Dyson has lived in Princeton, New Jersey, for over fifty years.

Dyson's father was the English composer Sir George Dyson; his mother was trained as a lawyer but after Dyson was born worked as a social worker. Despite sharing a last name, he is not related to the early 20th century astronomer Frank Watson Dyson, but as a small boy Freeman Dyson was aware of Frank Watson Dyson. Freeman credits the popularity of an astronomer with the same last name as having inadvertently helped to spark his interest in science.^{[citation needed]}

Dyson has six children, two of them (Esther and George) with his first wife, mathematician Verena Huber-Dyson, and the other four with his second wife, Imme Dyson, a masters runner who married him in 1958. Due to issues with some of his children not being recognized as British citizens he abjured his allegiance to Britain, and became a naturalized American citizen.