Magnetic spin phenomena in the chlorophyll “a” photoconductivity

Abstract

Magnetic Spin Phenomena in the Chlorophyll PhotoconductivityBY E. L. FRANKEVICH (a), M. M. TRIBEL (a), I. A. SOKOLIK (a), L. I. KOLESNIKOVA (a), and Yu. M. STOLOVITSEII (b)Modulation of the chlorophyll "a" (Chl) photoconductivity by an external magnetic field due t o variations of the rate of non-equilibrium spin processes under the action of a magnetic field is observed. These processes are charge carrier generation and charge detrapping by Chl triplet. Application of a magnetic field causes two types of variations of the photoconductivity of Chl films in vacuum: (i) instantaneous (t < 1 s) increase of the photoconductivity and (ii) slow decrease with time constant t = 10 to 100 8. The influence of temperature and intensity of the exciting light on the magnetic field effects is investigated. A scheme of energy transformation processes in Chl involving electron-excited and ionized states is presented. The presence of oxygen leads to an increase of the photoconductivity of Chl, as compared with the vacuum values, and to a change in the dependence of photoconductivity on magnetic field. These changes are shown to occur due to the appearance of new acceptor centres arising from unstable products of Chl photooxidation. Ha6~11onanacb MOAJ'JIFIUHR BHeUIHHM MarHHTHbIM EOJIeM BeJM9kIHbI @OTOIlpOBOnHMOCTH XJIOpO@HJIJIa "a", 06yCJIOBJIeHHaR M3MeHeHHeM B MarHHTHOM IIOJIe CKOpOCTefi HepaBHOBeC-HbIX CIlHHOBblX IIpOUeCCOB : 0 6 p a 3 0 B a H H R HOCIXTenefi T O K a H OCBO6O)KAeHHH 3 a X B a q e H H b I X JIOByUIKaMH 3 a p H n O B . YCTaHOBJleHO, YTO H a J r O W e H H e MarHHTHOrO XlOJIH BbI3bIBaeT n B a BHAa H3MeHeHHfi @OTOllpOBO~HMOCTH BaKYYMHPOBaHHbIX IIJIeHOK XJIOpO@HJIJIa C p a 3 J I H q -HOfi BpeMeHHOfi 3aBHCIXMOCTbIO : 6e3bIHepUHOHHOe (t < 1 8 ) YBeJIHqeHHe

Molecular spintronics

“…Frankevich has explained the magnetoconductance of photocurrent in terms of different g factors of hole and electron, operating on a loosely bound charge DD pair that might be Wannier exciton [102]. Magnetic field effects due to the DD pair mechanism seem to be more clearly observed in interface dynamics between different organic semiconductors [103][104][105][106], because the electron-hope pair, which might be sometimes called charge transfer exciton, is dominant species at the interface just after photoexcitation. For example, the intensity of the exciplex photoluminescence of electron-hole pair in the thin tetracene films on anthracene is reduced by a few percent by applying magnetic field of a few mT [103].…”