Unique spectroscopic properties of synthetic 15-cis beta-carotene, an important compound in photosynthesis, and a medicine for photoprotective function

The (11Bu+) energy of synthetic 15-cis β-carotene exhibits a linear dependence on (n2-1)/(n2+2) in non-polar and polar solvents; in this it is similar to (that of) all-trans β-carotene. The point of intersection is at (n2-1)/(n2+2) = 0.3 for both isomers. The microenvironment of 15-cis β-carotene in the Photosystem II reaction center was established as having a mean refractive index 1.473. Persistent spectral hole burning with a very broad (≈30 nm) hole observed around 500 nm (corresponding to an extremely short excited lifetime τ ≈9 fs) indicates that 15-cis β-carotene has/displays very efficient photoprotective quenching.