ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05878.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—When a system ofNsimilar molecules (the donors) gives its excitation energy rapidly enough to a dissimilar acceptor, the donor fluorescence rate equals the energy removal rate. Analysis of donor fluorescence decay then provides information about theN‐donor system even if the acceptor is chemically unidentified. The dependence of the removal rate onNin a linear polymer in the extreme limit of very strong interdonor coupling is compared with that of very weak interdonor coupling. The principal result is that removal can be slower in the strong coupling limit because standing‐wave excitons tend to avoid boundaries. Possible application of the concept of standing‐wave excitons to photosynthetic units is discussed. The theory of diffusive energy transfer (very weak coupling limit) is also discussed, and some of its basic formulas given in simp

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05879.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—This paper represents an attempt to understand the delayed luminescence behavior of a real (i.e. impure) mixed crystal. The growth and decay of delayed luminescence is analyzed and shown to be complex. The studies embrace guest and guest concentration dependencies, temperature dependence and excitation intensity and wavelength variation. It is shown that a simple model enables proper interpretation of certain limiting characteristics of the delayed luminescence growth and decay behavior. It is also shown that the temperature dependence of phosphorescence spectra of mixed crystals is readily rationalized and that the complex growth and decay behavior of real crystals are interpretable in terms of guest‐guest, guest‐trap and trap‐trap annihilation phenomena. Differences in the growth and decay lifetimes of a given luminescence are analyzed fully and the reasons for the differences substantiated experimentally. The systems studied consist of aromatics and simple amin

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05880.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—The photosensitized oxidations of rubrene by methylene blue and of diphenylan‐thracene by eosin have been studied where the sensitizer and the oxidizable substrate are separated by oxygen permeable layers of barium or cadmium stearate monomolecular films. The rate of the photosensitized oxidation reaction was followed by measurements of the hydrocarbon fluorescence, as a function of the stearate layer thickness. It has been found that the sensitized reaction is observable for thickness up to 500 Å and depends only on the deactivation process of the excited species (singlet oxygen) diffusing through the layers. It has been found also that half of the excited oxygen molecules are deactivated after a diffusion path of 115 A. The starting hydrocarbon can be regenerated by heating the sample after the photoreaction to approximately 120°C showing the transannular peroxide nature of the oxidation pr

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05881.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—The progressive reduction in temperature of hydro‐alcoholic mixtures is a way of associating aromatic molecules. It is possible to test the solute association, both by absorption and fluorescence measurements, of ‘polymerizable dyes' and solutes of biological interest. It is also possible to test the solute association by electron spin resonance of stable radicals (Wür‐ster's blue). The application of this technique to the study of photoprocesses was performed with flavin mononucleotide (FMN) by electron spin resonance and absorption spectroscopy in order to analyze the mechanism of photoreduction, and the stability of photo‐induced free radicals.The procedure of associating molecules by temperature effect in these solvents can be applied to the spectroscopic studies of the triplet state of aromatics in glassy solutio

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05882.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—A discussion is given of the photophysical and photochemical consequences of the binding of dyes and of pigments of biological importance to polymeric substrates. The modification of the photochemical properties induced by dye binding can in large part be ascribed to the known changes in photophysical properties of dyes engendered by such interactions. Principally, these involve enhanced formation of metastable species of dye molecules and decreased opportunity for self‐quenching. In photochemical terms, dye binding thus enhances susceptibility to photoreduction, causes an increase in the quantum yield of photoreduction with increasing concentration of bound dye, and induces enhanced ability to act as a sensi‐tizer in photoreduction. Paradoxically, dye binding decreases the ability of the bound dye to act as a sensitizer in photoxid

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05883.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—This paper reports the present conclusions of an extended investigation on photo‐sensitization of silver bromide. A general molecular packing structure for dye aggregates on the AgBr (111) surface is proposed. This structure, along with the observed spectral absorption displacements of small aggregates, is used to elucidate the phenomena of antisensitization and supersensitization. Supersensitization is seen as a partitioning of large dye aggregates into small aggregates by a deliberately added second component or by gaps between the aggregates. This partitioning isolates antisensitizing dye in a small fraction of the aggregates and minimizes its effect. The smallest aggregates are least likely to contain an antisensitizer, and show the highest quantum efficiency for photoconductivity and photographic action. Photoconductivity measurements establish that supersensitization occurs before the electron appears in the AgBr phase.The question of direct electron injection vs. energy transfer as mechanisms for AgBr photosensitization is examined in terms of radiationless transfer to surface Ag2S on AgBr. The absorption of surface Ag2S is shown to be adequate for acceptance of Förster transfer from the dye, and surface Ag2S is known to be photographically active. However, this mechanism is inefficient, and inadequate to account for observed high efficiency infrared sensitization. Direct electron injection is seen as the more probable mechanism for efficient dye sensitization of

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05884.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—The current status of research on sensitized photoconductive effects in zinc oxide is reviewed. The various types of chemical and spectral photosensitization processes observed in polycrystalline specimens can be explained qualitatively with a generalized electron acceptor molecule (EAM) model. in which electronegative surface agents trap zinc oxide conduction electrons in the dark and illumination causes a release of the trapped electrons. The EAM may be an adsorbed gas or vapor, adsorbed dye molecules, or an aggregated dye film, depending on the particular photoeffec

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05885.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—The electron affinities and ionization potentials of amorphous sulfur, vitreous selenium and several phthalocyanines were measured by Nelson's electron beam retardation method and photoelectric emission, respectively. The electron affinities (Ac) measured were: 4.5 eV for sulfur, 3.4eV for selenium, and approximately 4.3 eV for all the phthalocyanines measured. Photoemission thresholds (Ic) were 7.0 eV for sulfur and 6.0 eV for selenium. Two photoionization thresholds (at about 5.2 and 6.1 eV) were found for both α‐copper and α‐metal‐free phthalocyanine; the former is attributed to impurity levels, the latter to bulk states. In each case, the band gap calculated fromIcand Acwas found to be approximately equal to the optical threshold for photocon

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05886.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—The photoconductivity of thin films of poly(N‐vinyl carbazole), and poly(N‐vinyl carbazole) sensitized with a thin layer of amorphous selenium, has been measured using a ‘xerographic’ condenser discharge technique and a conventional time of flight light pulse photo‐response technique. Direct camer generation and hole mobility in the polymer was found to be strongly field dependent. There appears to be no evidence for deep trapping. Hole transport through the polymer was able to be sensitized by light absorbed in the selenium. The results indicate that the photosensitization mechanism can be thought of in terms of hole generation and transport in selenium, field‐modulated injection across the selenium polymer interface and transport throug

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05887.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY