Several skin-sensitizing psoralens and their model coumarins fluoresce weakly and phosphoresce relatively strongly. The excited states of some of these molecules have been investigated in rigid matrices at 12 and 77 °K by means of luminescence and photoselection measurements. Coumarins and psoralens exhibit a relatively high phosphorescence to fluorescence ratio ( / > 1); however, in coumarylpyrone (benzo[l,2-6:4,5-6']dipyran-2,8-dione) and coumarins with strong charge transfer substituents, the ratio is significantly less than unity. In coumarylpyrone this is interpreted as being due to a decreased efficiency of the intersystem crossing from 8 ( , *) to ( , *) as a consequence of the lowering in energy of the ( , *) state below the 3( , *) state. For the series of molecules investigated, it was established that the 0-0 phosphorescence frequencies, ¡Vo, are essentially independent of substituents or the extent of conjugation. This result reinforces the model of energy localization in the 3( , *) state as proposed previously for coumarin and psoralen. The electronic structures of the excited states of selected compounds calculated by SCF-MO methods are consistent with this model. The MO data as well as the spectroscopic data may be correlated with the photobiological reactivity of these molecules toward DNA.Coumarins, particularly psoralens, are known to photosensitize skin erythema and skin cancer in mice and guinea pigs, though skin cancer in man is not unequivocally established.3•4 56The skin-sensitizing potency of psoralens has been correlated with their photoreactivity toward pyrimidine bases of DNA via cycloaddition.3•5-7 In an attempt to describe the electronic mechanism involved in the photocycloaddition of skin-sensitizing compounds to DNA bases, we have previously studied the excited states of coumarin as a model skin sensitizer.7 8 The present paper summarizes more complete studies, many at high resolution, of the excited states of a series of coumarins and psoralens.By far the most interesting molecule examined in this study is coumarylpyrone, benzo[ 1,2-6:4,5-6 'jdipyran-2,8-dione. The impetus for considering this particular system (and its analog benzo[l,2-6:4,5-6'Jdipyran-2,7-dione, which is yet to be synthesized) arose out of a previous work7 concerned with the photocycloaddition of the excited coumarins to DNA bases. In this work it was suggested that the triplet state of coumarin and its derivatives undergoes cycloaddition (at the 3,4 double bond) with pyrimidine bases of DNA. Two such double bonds within the molecular framework as found in coumarylpyrone would theoretically provide two active sites with an opportunity to crosslink both strands of the DNA double helix. Figure 1 shows the structures and numbering systems for coumarin, psoralen, isopsoralen, and coumarylpyrone.

No abstract

We present a novel approach to optical mammography and initial clinical results. We have designed and developed a frequency-domain (110-MHz) optical scanner that performs a transillumination raster scan of the female breast in approximately 3 min. The probing light is a dualwavelength (690 and 810 nm, 10-mW average power), 2-mmdiameter laser beam, and the detection optical fiber is 5 mm in diameter. The ac amplitude and phase data are processed with use of an algorithm that performs edge effect corrections, thereby enhancing image contrast. This contrast enhancement results in a greater tumor detectability compared with simple light intensity images. The optical mammograms are displayed on a computer screen in real time. We present x-ray and optical mammograms from two patients with breast tumors. Our initial clinical results show that the frequencydomain scanner, even at the present stage of development, has the potential to be a useful tool in mammography.As the number-one killer of women, breast cancer annually fells more than 44,000 women in the United States alone.