Optically excited triplet states in the bacteria Rhodopseudomonas sphaeroides ‘wild-type’ detected by magnetic resonance in zero-field

Abstract

Optically-detected magnetic resonance (ODMR) experiments in zero-field on the photosynthetic bacteria Rhodopseudomonas sphaeroides revealed triplet states belonging to molecules which have a prompt emission in the optical region from 590 to 700 nm and a delayed emission between 700 and 830 nm. The zero-field parameters of these triplet states are 29 <| D|< 34 · 10 −3 cm −3 and 4 <| E|< 8 · 10 −3 cm −1, the decay rates of the | D|+| E| transitions being in the order of 60–340 ms. The correlation between optical emission and radio-frequency was used to separate the total optical emission from 590–700 nm into individual emissions, belonging to molecules whose triplet states were studied by ODMR in this region. Comparing the fluorescence microwave double resonance (FMDR) spectra with the results of excitation spectroscopy, as well as comparing the zero-field parameters and the decay rates with that of Mg-porphyrins in matrices given in the literature, allowed the identification of the emitting molecules as Mg-porphyrins which are produced by the biosynthesis of bacteriochlorophyll in the cells.