Knowledge Bank

We have observed the zero-field magnetic resonance transitions of the lowest triplet state of a series of chlorophyll molecules at $2\circ K$ using methods of optical detection of magnetic resonance (ODMR). The rates of intersystem crossing for the individual spin sublevels have been measured and are found to depend dramatically on the nature of the ring substituents and metal center. These results will be explained by a qualitative consideration of one-center spin-orbit and vibronic spin-orbit coupling mechanisms available to the particular chlorophyll molecule. Also, we have observed sharp, structureless zero-field triplet state transitions of chemically reduced whole cell preparation of photosynthetic bacteria. These results will be presented and discussed.