THE ORIENTATION OF THE TRIPLET AXES WITH RESPECT TO THE OPTICAL-TRANSITION MOMENTS IN (BACTERIO)CHLOROPHYLLS

Chlorophyll a (Chl a), bacteriochlorophyll a (BChl a) and bacteriochlo rophyll g (BChl g) were studied by absorbance-detected magnetic resona nce (ADMR) and linear-dichroic (LD-) ADMR in zero magnetic field using two different glassy matrices. The microwave-induced triplet-minus-si nglet absorbance-difference spectra were measured in the wavelength re gion 500-900 nm. With LD-ADMR the orientations of the near-infrared si nglet-singlet and triplet-triplet transition moments relative to the i n-plane triplet x and y axes were obtained. For all (B)Chls studied, t he Q(Y)- and near-infrared triplet-triplet transition moments are mutu ally parallel (within 5 degrees), and oriented in the triplet xy plane . For BChl a and BChl g the Q(Y)-transition moment was found to be ori ented within 20 degrees parallel to the triplet y axis. For Chl a the orientation of the Q(Y)-transition moment with respect to the triplet y axis was found to be 35-45 degrees, the precise value depending on t he solvent used.