We measured circular dichroism (CD) of hydrated and non-hydrated powder crystals of cobaloxime complex. The CD spectrum was found to depend on the crystalline forms. Non-hydrated crystals exhibited an extra pair of exciton-split CD peaks associated with the chiral molecular arrangement in the crystals. We also made direct observation of a photo-induced chirality change or switching in the alkyl ligand of the cobaloxime complex in both crystalline forms. (c) 2006 Elsevier B.V. All rights reserved.