The Optical Properties of Molecules
and Chromogenic Aggregates of Xanthene Dyes

Yu. A. Mikheev^a, L. N. Guseva^a, and Yu. A. Ershov^b

^a Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, ul. Kosygina 4, Moscow, 117977 Russia

^b Bauman State Technical University, Vtoraya Baumanskaya ul. 5, Moscow, 107005 Russia

e-mail: mik@sky.chph.ras.ru

Received March 11, 2008

Abstract—The UV absorption spectra of rhodamine B and G molecules isolated from industrial dye samples
were obtained. Two procedures were used. In one of them, rhodamine B molecules were displaced with water
into a heptane layer from a solution of the dye in an alcohol–heptane mixture. The second procedure involved
heating of the dye introduced into cellulose triacetate films. Individual rhodamine molecules (namely, dye cat-
ion–chlorine anion ion pairs) prepared by both methods did not absorb visible light. The spectra of individual
rhodamine molecules coincided with the spectra of so-called pseudoleucobases of xanthene dyes reported in
the literature. The conclusion was drawn that the chromaticity property in the series of xanthene dyes appeared
because of the formation of supramolecular dimeric and larger aggregates, as was earlier established for triph-
enylmethane dyes (TPMDs) and copper phthalocyanine (CuPc). At the same time, individual xanthene dye
molecules, like TPMD and CuPc molecules, are not chromogens.

DOI: 10.1134/S0036024409050197

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