San Antonio; and the JLaser Branch, Directed Energy Division, Occupational and Envi-ronmental Health Directorate

Irradiation of the primate lens by near-ultraviolet wavelengths results in a blue fluorescence, which can be an intraocular source of veiling glare. This study quantitated the fluorescence intensity as a function of exciting intensity and wavelength. As the exciting wavelength was increased from 360 to 430 nm, the decreasing fluorescence intensity (for equal radiant exposures) was partially offset by a shift in the fluorescence spectrum to wavelengths of greater luminous efficiency so the luminance of the lens fluorescence remained approximately constant. The measured luminance of the lens fluorescence was high enough to imply degradation of visual function as a result of reduced contrast of the retinal image. To obtain an objective measure of visual deficit associated with the fluorescent glare, the visual evoked potential (VEP) elicited by counterphased sine-wave gratings was recorded while the subject eye was continuously exposed to the 413 nm emission from a krypton laser. The VEP amplitude was reduced in the presence of the exciting laser even at levels defined as "safe" (ie, where exposure levels are insufficient to induce an acute ocular lesion). Because the direct glare effect of the exciting radiation was negligible in this experiment, the VEP response loss is attributed to the effect of the lens fluorescent glare. Invest Ophthalmol Vis Sci 33: [410][411][412][413][414][415]1992 The ocular lens of the primate fluoresces in the blue when irradiated by near-ultraviolet (UV) wavelengths. This phenomenon, although usually unnoticed, is nevertheless present with exposure to the ambient solar environment. In the aging lens, the near-UV absorption band broadens and encroaches into the blue, while the fluorescence intensifies and migrates toward longer wavelengths. 1 ' 2 Weale has estimated 3 that the reciprocal ratio between the luminance of a patch of sky and that of the fluorescence it induces is ~ 0.002 for the normal lens of a 30-year-old human (generally unnoticeable) but increases to 0.017 for a 60 year old (generally noticeable) and to 0.121 for an 80 year old. In the latter case, the fluorescence can be an intraocular source of "veiling glare," covering the entire field of view and intensity enough to impair visual function. With certain disease pro

Wavelength dependent triplet state populating mechanisms of naphthalene in heavy atom hosts

We have made zero-field optically-detected magnetic resonance measurements on the triplet state of naphthalene-d8 incorporated in the heavy-atom host crystals p-dichlorobenzene, p-dibromobenzene, and s-tetrachlorobenzene. The dependence of the relative triplet sublevel populating rates on the exciting wavelength is interpreted in terms of the electronic excitation transfer mechanisms. We find that upon excitation of the host S1 ← S0 transition in p-dichlorobenzene, energy transfer to the guest T1 takes place via the guest S1, whereas in the other host crystals the intermediate is mainly the host T1 band. Upon host T1 ← S0 excitaton, trapping takes place from a spin-aligned excitor band in s-tetrachlorobenzene, whereas the initial alignment is lost prior to trapping in the dihalobenzene hosts

Kinetics of the triplet state of 2,3-dichloroquinoxaline from microwave-induced phosphorescence transients

The phosphorescent state of 2,3-dichloroquinoxaline doped into single crystals of durene and 1,2,4,5-tetrachlorobenzene has been studied using several methods based upon optical detection of magnetic resonance (ODMR). Flash excitation and continuous optical pumping methods are described and analysed. Phosphorescent transient effects caused by spin-lattice relaxation and variable intersystem crossing rates are observed and described using first-order solutions of the appropriate rate equations. The effects of spatial polarization of the phosphorescence (anisotropic spatial distribution of phosphorescence intensity) of single crystals on ODMR signals is observed and discussed. The spatial polarization of emission can cause difficulties in determining relative radiative rate constants of the triplet sublevels in oriented samples, but can yield information about the linear polarization of the emission analogous to that obtained by conventional means using polarizers

Optically detected magnetic resonance of the tryptophan phosphorescent state in native proteins

The phosphorescent triplet state of tryptophan has been studied by the method of optically detected magnetic resonance (ODMR) at pumped helium temperatures in zero magnetic field. Only one of the triplet sublevels is found to be significantly radiative; the other two decay radiationlessly. Although the phosphorescence and ODMR decay lifetimes are influenced by spin-Ianice relaxation processes at T = 1·3°K. the lifetime of the radiative level can be estimated as approximately 2 s, whereas the lifetimes of the non radiative levels are in excess of 10 s. Comparison of the ODMR signals and the phosphorescence spectra has been made for tryptophans in native proteins with the following results: the ODMR signals of the two types of tryptophan sites in horse liver alcohol dehydrogenase can be resolved due to a shift in the D and E values of the respective triplet states; binding of the substrate tri-N-acetylglucosamine to hen lysozyme leads to a considerable narrowing of the phosphorescence peaks and ODMR signals as well as to a shift in the E value oflhe triplet state. The following tentative conclusions can be reached: the tryptophan triplet D and E values are measurably affected by the environment of the chromophore in the protein, as are the linewidths of the magnetic resonance transitions. The IEI value is reduced and the magnetic resonance linewidth is increased with increasing exposure of the tryptophan to hydroxylic solvent. Although a considerable part of the width of the magnetic resonance transition can be ascribed to a heterogeneity of environments in the sample, there appears to exist an intrinsic line-broadening process which at present is not understood

Characterization of protein triplet states by optical detection of magnetic resonance

The technique of optical detection of magnetic resonance (ODMR) is applied for the first time to the study of molecules of biological interest in frozen glassy solutions. We present results describing the triplet state properties of tryptophan, tyrosine, and the tryptophan and tyrosine residues of bovine serum albumin