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The Luminescence of Chlorophyll-Containing Plant Material

Description: The luminescence of various chlorophyll-containing plant materials has been investigated under a variety of conditions. The results have been shown to be consistent with a mechanism involving the recombination of electrons and holes trapped in a quasi-crystalline lattice. Some details of such a mechanism have been proposed which suggest the mode of entry of the light energy into the photosynthetic pathway.
Date: July 1, 1957
Creator: Tollin, Gordon & Calvin, Melvin
Partner: UNT Libraries Government Documents Department

Energy Conversion in Photosynthetic Processes

Description: The concepts of solid-state photophysics are applied to biological materials, especially particulate matter derived from green plants. Photoinduced electron-spin resonance signals have been observed in isolated chloroplasts and other green plant materials; their growth time is not affected by reducing the temperature to -140 C. The luminescence of these materials has also been investigated under a variety of conditions. The results of these studies have been shown to be consistent with a mechanism involving the recombination of electrons and holes trapped in a quasi-crystalline lattice. Some details of such a mechanism have been proposed that suggest the mode of entry of the light energy into the photosynthetic pathway.
Date: March 10, 1958
Creator: Tollin, Gordon; Sogo, Power B. & Calvin, Melvin
Partner: UNT Libraries Government Documents Department

ELECTRICAL PROPERTIES OF ORGANIC SOLIDS. I. KINETICS AND MECHANISMOF CONDUCTIVITY OF METAL-FREE PHTHALOCYANINE

Description: Techniques involving the use of high-intensity short-duration light pulses have been applied t o the study of the kinetics of photoconductivity in films of metal-free phthalocyanine. These experiments, in conjunction with measurements of steady-state photoconductivity, are consistent with the following scheme. The principal route for the formation of charge carriers is via the first excited singlet state, although the lowest triplet state can, t o some extent, contribute to charge - carrier production. The mobility of the carriers is low and is concentration-dependent, being lower at higher carrier concentration. The decay of the photocurrent is the result of a diffusion-limited bimolecular recombination, with a capture radius of approximately one molecular diameter. The experiments indicate that carriers produced thermally in the dark do not interact with light-produced carriers.
Date: July 29, 1959
Creator: Tollin, Gordon; Kearns, David R. & Calvin, Melvin.
Partner: UNT Libraries Government Documents Department

ELECTRICAL PROPERTIES OF ORGANIC SOLIDS. II: EFFECTS OF ADDEDELECTRON ACCEPTOR ON METAL-FREE PHTHALOCYANINE

Description: The addition of ortho-chloranil to the surface of films of metal-free phthalocyanine has been found (a) to increase the dark conductivity of such films by as much as 10{sup 7}, (b) to increase the steady-state photoconductivity by as much as 10{sup 5}, and (c) to result in the formation of unpaired electrons whose concentration decreases reversibly as a result of illumination. These systems exhibit a light-induced polarization, the phthalocyanine layer becoming more positive with respect t o the ortho-chloranil layer. Kinetic studies demonstrate that, upon illumination, a single process (time constant = 40 seconds) results in the increase in conductivity, the decrease in unpaired spins, and the increase in polarization. The results are consistent with the following scheme. An electron transfer from phthalocyanine to ortho-chloranil occurs in the dark at room temperature, producing holes in the phthalocyanine layer and ortho-chloranil negative ion radicals (high conductivity, ESR signal). Illumination results in the transfer of an electron from an excited phthalocyanine molecule to the ortho-chloranil negative ion, producing further phthalocyanine holes and ortho-chloranil double-negative ion (increase in conductivity, increase in polarization, decrease in ESR signal). By equating spin concentration with charge - carrier concentration (phthalocyanine holes) it is possible to calculate a mobility of 10{sup -4} cm{sup 2}/volt/sec for holes in the phthalocyanine layer. By use of this value, a quantum yield of unity is calculated for the production of charge carriers in doped phthalocyanine. The experiments indicate a quantum yield of less than 10-1 for undoped phthalocyanine. The over-all results of adding a strong electron acceptor to a film of phthalocyanine are thus t o (a) produce charge carriers in the dark, (b) increase the quantum yield for production of charge carriers by light, and (c) increase charge-carrier lifetime.
Date: July 29, 1959
Creator: Kearns, David R.; Tollin, Gordon & Calvin, Melvin
Partner: UNT Libraries Government Documents Department