Optically induced electron spin polarization in the triplet state of chlorophyll and its model compounds

Abstract

Optically induced electron spin polarization (OEP) is reported for the triplet state of chlorophyll-a and -b in an organic glass at 15 K and for tetraphenyl porphyrin (TPP) and -chlorin (TPC) free base in a solid polymer up to ≈ 200 K. Such polarization results in emissive transitions in the Δ m = ± 1 ESR spectrum during continuous illumination of these compounds. From the experimental results it is concluded that both chlorophylls have dominant steady-state population in the top zero-field level, associated with an arbitrary in-plane molecular axis. The amount of spin-polarization is strongly affected by the rigidity of the medium as is demonstrated by the observation of emissive transitions in the Δ m = 1 triplet spectra of TPP and TPC up to ≈ 200 K.