Violet Light Elicits a Pronounced Response from Zeaxanthin and Retinal in Model Lipid Membranes and the Human Retina

Zeaxanthin is a carotenoid concentrated in the macula lutea of the human retina. This pigment can interact with retinal molecules in membranes due to the visual cycle, which operates in both protein and lipid environments. Here, we show that zeaxanthin and retinal present in the membranes exhibit very pronounced photochemical phenomena specific to violet light (405 nm). These include driving the photoisomerization of retinal and zeaxanthin. We interpret these observations in the context of molecular mechanisms resulting from the formation of zeaxanthin-zeaxanthin and zeaxanthin-retinal dimers, which specifically absorb violet light. Possible photophysical processes postulated for excited dimers include the decay of the singlet state into two triplet states (singlet–triplet-fission), followed by pigment isomerization involving the triplet state. We discuss the possible physiological significance of violet light-induced photoisomerization of retinal and zeaxanthin in the functioning of the human eye.