DEUTERATION EFFECT ON PHOTOINDUCED HYDROGEN MOTIONS IN LOW-TEMPERATURE MIXED MOLECULAR-CRYSTALS

Irradiation at liquid helium temperatures of benzoic acid crystals doped with pentacene leads to a reversible bleaching of the pentacene absorption and the appearance of defect sites related to a rearrangement of the acid protons of the host. Upon deuteration of these acid protons a partial H/D exchange in pentacene during the crystal growth is observed. Different partially deuterated pentacene molecules give rise to distinct 0-0 bands. Selective and non-selective laser irradiations show that the yield of the reaction leading to the appearance of the defect sites varies strongly as a function of this partial deuteration of the guest pentacene molecule.