Redshift Resolution

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Science  12 Sep 2008:
Vol. 321, Issue 5895, pp. 1419
DOI: 10.1126/science.321.5895.1419a

Dyes operate by absorbing specific wavelengths of light, thereby changing the overall color we perceive in looking at a dyed liquid or solid. In general, though, the color a dye confers depends not only on its molecular structure but on the medium in which it's been dissolved or suspended. Renger et al. derive a remarkably simple relation for predicting how the electronic absorption spectrum of an isolated nonpolar dye molecule will shift upon dissolution in a nonpolar solvent. In contrast to polar media, the influence of the weaker and more rapidly varying charge distributions in nonpolar media has remained puzzling. A prevailing model derived more than 50 years ago suggested that the absorption spectrum should shift to longer (redder) wavelengths as the strength of the absorption increased. However, the authors show that instead, the shift scales with the energy of the state accessed by the light absorption. They support their relation by accurately predicting spectral shifts for the bacteriochlorophyll a and bacteriopheophytin a chromophores. — JSY

Proc. Natl. Acad. Sci. U.S.A. 105, 13235 (2008).

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