Knowledge Bank

The nature of the excited state level ordering in 11-cis retinal is investigated using solvent effect and temperature effect absorption spectroscopy. The vibrational-electronic structure appearing in the 30 000 -- 38 000 $cm-1$ region at reduced temperatures (4 -- $77\circ K$) is identified with the $\Pi \ast$ $\leftarrow n$ transition. Implications of this assignment for retinal photochemistry are discussed.