We present vertical excitation properties calculated using Time-Dependent Density Functional Theory (TD-DFT) and Resolution of Identity second-order coupled cluster (RI-CC2) methods for the lowest energy states of 11-Z-cis retinal and the recently synthesized 11-Z-cis-7,8-dihydro retinal. Within 11-Z-cis retinal the lowest expected energy transition is from the HOMO (pi) to LUMO (pi*), which results in the known isomerization. Contrary to 11-Z-cis retinal, the lowest energy transition within 11-Z-cis-7,8-dihydro retinal possesses some charge transfer character, and it is in fact the second lowest energy excitation from HOMO-1 (pi) to LUMO (pi*) which could lead to the experimentally observed isomerization. (C) 2009 Elsevier B. V. All rights reserved.