Photochemical hole burning of 1,4-dihydroxyanthraquinone intercalated in a pillared layered clay mineral

A tetramethylammonium-saponite-1,4-dihydroxyanthraquinone intercalation compound was prepared and a persistent spectral zero-phonon hole was obtained at liquid helium temperatures by Kr⁺ laser light irradiation (520.8 nm). This is the first example of persistent hole formation of 1,4-dihydroxyanthraquinone in crystalline inorganic matrices. In spite of the high concentration of 1,4-dihydroxyanthraquinone (ca. 1.5 mol kg^-1), a narrow hole with the initial width of 0.25 cm^-1 (4.6 K) was obtained with no distinct decrease in burning efficiency (>1.0 × 10^-4) if compared with those doped in ordinary polar polymers or organic glasses. The microscopic geometry of the compound is discussed on the basis of hole formation properties as well as X-ray powder diffraction and ¹³C NMR observation.