1. Chemistry Lecture Notes Light and Vision

2. smaller  E  lower frequency, longer wavelength Absorption of light in conjugated systems conjugated double bonds molecular orbitals: ground stateexcited state

3. found in carrots and some yellow and green vegetables found in fish-liver oils and dairy products max = 450 nm (absorbs in blue, appears orange)  -carotene and retinol

4. Geometric isomers  single bonds are free to rotate  no free rotation in double bonds cis-2-butenetrans-2-butene geometric isomers (a class of stereoisomers)

5. The primary vision process

6. The overall vision process

7. Vision Event Occurs With Blinding Speed The time scale for the primary event in vision is faster than expected, according to researchers in Berkeley, CA. Their measurements show that the first step in vision, the 11-cis  11-trans isomerization of the rhodopsin chromophore, is essentially complete in only 200 femtoseconds, making it one of the fastest photochemical reactions ever studied. Rhodopsin consists of the 11-cis retinal prosthetic group bound within the protein opsin. It was determined in 1963 that the absorption of light results in isomerization of 11-cis retinal to form the trans photoproduct, bathorhodopsin. Although previous studies have suggested that the isomerization occurs in less than a picosecond, the time scale for the formation of the primary photoproduct had never been experimentally determined. An advance earlier this year by Schoenlein and Shank in the generation of femtosecond laser pulses in the blue-green spectral region made it possible to study the ultrafast process.