WorldCat Identities


Works: 5 works in 5 publications in 1 language and 5 library holdings
Publication Timeline
Radiationless deactivation and anomalous fluorescence of singlet 1,12 benzperylene( Book )

1 edition published in 1968 in English and held by 1 WorldCat member library worldwide

Values of the rate constants for processes that deactivate the lowest excited singlet state of 1,12 benzperylene were determined between -196C and 23C from measurements of the quantum yields of triplet formation, fluorescence, and the fluorescence lifetime. The rate constant for intersystem crossing to the triplet state is nearly same at -196C and +23C. The rate constant for direct radiationless deactivation to the lowest singlet is probably zero at -196C but increases to 600000/sec at +23C. This is similar to results obtained for other aromatic hydrocarbons. However, the fluorescence of 1,12 benzperylene is atypical. An increase in the rate constant of fluorescence, k1, from -196C to +23C is observed resulting from an increase in fluorescence with temperature while fluorescence lifetime decreases over the same temperature range. The increase in k1 with increasing temperature is attributed to a temperature dependent emission from the second excited singlet state. Since the second excited singlet state of 1,12 benzperylene lies only 1275 to 1400/cm above the (1)Lb state, there is significant thermal population of the (1)La state of +23C. The observation of a temperature dependent anti stokes fluorescence supports this interpretation. The effect of solvent upon the energy gap between the (1)La and (1)Lb state and the fluorescence properties of 1,12 benzperylene is discussed. (Author)
Photochromic eye-protective device based on triplet absorption( Book )

1 edition published in 1966 in English and held by 1 WorldCat member library worldwide

A prototype 6 x 8-inch photochromic windshield segment was developed and delivered to the Air Force. The device is designed to protect pilots against flash blindness caused by exposure to nuclear explosions. The reversible photochromic darkening is based upon absorption of visible light by metastable triplet states of aromatic molecules. The active compounds are incorporated into solid sheets of transparent plastic. Three sheets of plastic are arranged in an N-type configuration and the triplet states are produced by UV excitation from two flash lamps. Black glass filters prevent visible light from the flash lamps from dazzling the observer. With a 1900 joule input to the flash lamps, the triplet-state windshield segment attains within one millisecond an optical density, weighted for eye-response, that varies from 1.4 along a line midway between the flash lamps to 2.7 close to each flash lamp. The open-state transmittance is 65% and the device re-opens to one-half this transmittance in approximately 2 seconds. (Author)
Research on triplet states and photochromism( Book )

1 edition published in 1965 in English and held by 1 WorldCat member library worldwide

A normally transparent screen is needed that can be darkened quickly enough to protect the eyes of combat pilots who may be exposed to flashes from nuclear explosions. Strong absorption of visible light from the lowest triplet level of selected aromatic compounds is a promising basis for development of the required screen for prevention of flashblindness. This triplet absorption, which may be induced by absorption of ultraviolet light from microsecond flash lamps, decays in a few seconds so that transparency is spontaneously restored. A method of measuring extinction coefficients of triplet absorption and quantum yields of triplet formation has been developed. Combinations of aromatic compounds giving strong triplet absorption of visible light over the visible spectrum with minimized excitation energy are selected on the basis of these results. Two promising compounds have been synthesized. New plastics having greater solubility for large aromatic molecules than polymethylmethacrylate have been found. A method of making large sheets of polymethymethacrylate with exceptionally high transparency to ultraviolet is described. Deleterious effects of exposure of plastics, with and without aromatic solutes, to oxygen and sunlight have been studied. It was shown that diffusion of oxygen into the plastic sheets may be greatly reduced by a polyvinyl-alcohol coating. The application of these experimental results to the design of a protection device against flashblindness is discussed. (Author)
Radiative and radiationless processes in aromatic molecules: pyrene( Book )

1 edition published in 1968 in English and held by 1 WorldCat member library worldwide

The fluorescence yield, triplet yield, and fluorescence lifetime for pyrene-h10 and pyrene-d10 have been measured as a function of temperature. The phosphorescence yield, and phosphorescence lifetime, have also been determined. However, in pyrene-d10 the fluorescence yield increases with increasing temperature, indicating that the rate constant for intersystem crossing has a temperature-dependent part. The variation of fluorescence lifetime and triplet yield with temperature for a pyrene-h10 is attributable in toto to a temperature-sensitive internal conversion; in pyrene-d10 both internal conversion and inter-system crossing are temperature-dependent and contribute to the observed variations. (Author)
Fluorescence and phosphorescence of aromatic hydrocarbons in poly(methylmethacrylate) as a function of temperature( Book )

1 edition published in 1968 in English and held by 1 WorldCat member library worldwide

Fluorescence lifetimes (t) and fluorescence yields(P) of poly(methylmethacrylate) samples containing coronene-h12, coronene-d12, pyrene-h10, pyrene-d10, 1,2;5,6 dibenzanthracene, 1,2;7,8 dibenzanthracene, 1,2;3,4 dibenzanthracene, 1,2 benzcoronene and 1,12 benzperylene were measured. For all compounds studied, except coronene-h12 and coronene-d12, t decreases with increasing temperature. For all compounds except 1,12 benzperylene and 1,2;3,4 dibenzanthracene, P decreases proportionally with t so that the radiative lifetime (t) is temperature independent. For the two last mentioned compounds t varies with temperature. This may be due to the closeness of the p band to the lowest-lying alpha band. The activation energies of temperature dependent quenching of t are all similar. The quenching is related to Lin's theory of radiationless transitions and it is suggested that this temperature dependent quenching is due to S1 -- So transitions. (Author)
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