Magnetophotoselection Study of the Lowest Excited Triplet State of the Primary Donor in Photosynthetic Bacteria

Abstract

The first time-resolved magnetophotoselection study of the primary donor triplet state ( 3 P) in bacterial reaction centers from Rhodobacter sphaeroides R26 and Rhodopseudomonas Viridis is reported. With direct excitation of the primary donor, this approach provides the orientation (spherical coordinates δ, colatitude, and γ, longitude) of the excited optical transition moment in the principal triplet axis system. It is essentially free from the effects of spin-lattice relaxation of 3 P, enabling magnetophotoselection measurements over a wide temperature range. Two independently measured triplet-state spectra, excited with light polarized parallel and perpendicular to the EPR magnetic field, are simulated with the same set of parameters. This procedure results in a high precision (ca. (5°with sufficient signal/noise ratio) of the obtained spherical coordinates of the optical transition moment vector. We find δ ) 80 ( 5°, γ ) 70 ( 5°and δ ) 75 ( 5°, γ ) 70 ( 5°for Rb. sphaeroides R26 and Rps. Viridis, respectively. We demonstrate that excitation of the sample with nonpolarized light is essentially nonisotropic. Neglect of this effect in spectral simulations of light-induced signals may lead to considerable error in the parameters determined.

Charge-Transfer Character Drives Möbius Antiaromaticity in the Excited Triplet State of Twisted [28]Hexaphyrin

“…To determine the orientation of the principal D -tensor axes with respect to the transition dipole moment ( M ) in [28]­Hex , MPS analyses were examined in Figure at 0.5 μs. − In the present MPS measurements, 650 nm light was selected to photoexcite [28]­Hex based on the UV–vis absorption peak (Figures S2 and S3) corresponding to the M direction parallel to the short molecular axis, as reported in a previous study . The computed M in Figure was consistent with the absorption band at around 650 nm at 77 K (Figure S2), as explained previously .…”

Low-Temperature Pulsed EPR Study at 34 GHz of the Triplet States of the Primary Electron Donor P865and the Carotenoid in Native and Mutant Bacterial Reaction Centers ofRhodobacter sphaeroides

“…Also, the latter frequency is the sum of the former two frequencies, which shows that 7.8 MHz concerns the double quantum transition and that all frequencies stem from the M S = 0 manifold (see figure 5a). Taking advantage of the fact that no hyperfine interaction is present in the M S = 0 level, an estimate of the size of the quadrupole interaction for the pyrrole nitrogens can be made by using the formula (38) (4) where ν Z is the Zeeman frequency for 14 N, e 2 qQ/h and η are the nuclear quadrupole coupling parameters (42). The asymmetry parameter η is defined as (5) where Q xx , Q yy and Q zz are electric field gradients at the nitrogen.…”

Transient Electron Spin Polarization Imaging of Heterogeneous Charge-Separation Geometries at Bulk-Heterojunction Interfaces in Organic Solar Cells

“…We characterized the interfacial CS geometries and their electronic couplings in the active layer by supporting detections of light polarization direction ( L ) effect of the excitation laser on the TREPR spectrum with respect to the B 0 direction on the P3HT:PC 61 BM blend films applying L // B 0 and L ⊥ B 0 . This L effect has been referred to as magnetophotoselection (MPS) and has long been demonstrated to be useful to determine the orientations of the spin–spin dipolar interactions. − We herein characterized two different TREPR components possessing different spin–spin geometries and relaxation times in the CS states due to the disorders.…”