Intercalation of Rhodamine 6G and Oxazine 4 into Oriented Clay Films and Their Alignment
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Ryo Sasai Research Center for Advanced Waste and Emission Management (ResCWE), Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
Taketoshi Fujita and Kenji Kitamura Advanced Materials Laboratory (AML), National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan (Received 22 October 2001; accepted 9 February 2002)
The cationic dyes rhodamine 6G (R6G) and oxazine 4 (Ox4) were intercalated into oriented lithium hectorite (LiHT, a synthetic fluor-mica) films by ion-exchange, and their orientation was studied by x-ray and polarized spectroscopy. Orientation of dyes was determined by basal spacing obtained by x-ray diffraction data, showing that angles of the long axis were 60° for R6G and 47° for Ox4 against the layer. Polarized ultraviolet-visible spectroscopy showed that the high-order H-aggregate of R6G and Ox4 were oriented at 64° and 52° against layers, respectively; other states of dyes were oriented at much lower angles. The interlayer distance was mostly determined by dimensions of the high-order H-aggregate.
I. INTRODUCTION
Intercalation of organic compounds into inorganic layered silicates has attracted wide scientific and practical interest. By studying and adjusting properties of the host, guest, and intercalation reactions, we design materials with unique structures, novel chemical and physical phenomena, and enhanced mechanical properties. This has been extensively studied in such fields as intercalation of cationic surfactants into clay minerals,1–3 preparation of polymer/clay nanocomposites,4 –7 adsorption of poorly water-soluble organic pollutants,8,9 and the control of photophysical and photochemical reactions in restricted geometry.10–12 Many publications have described clay–dye interactions.13–28 López Arbeloa et al.14,15 studied the metachromasy phenomenon and formation of aggregates (dimer, trimer, etc.) of rhodamine 6G (R6G) in clay colloid suspensions by absorption and emission spectroscopy. Yariv et al.17,18 reported similar phenomenon for dyes in clay suspensions. Most reports focus on dye adsorption or intercalation in colloidal suspensions, but few discuss solid-state systems, e.g., work by Fujita et al.25 Orientation of dye in the interlayer space of
synthetic mica (taeniolite) was studied and it was concluded that R6G molecules were oriented with their long axis perpendicular to clay layers by 1-dimensional Fourier analysis using powder x-ray diffraction (XRD) data. Sasai et al.26 applied polarized ultraviolet-visible (UVvis) spectroscopy to the same R6G/taeniolite complex, showing results consistent with Fujita et al.25 For practical application of hybrids of functional organic dyes with clay minerals, intercalation, orientation, and aggregation of dyes in a solid state, such as thin films, require further study. This paper deals with the intercalation of 2 cationic laser dyes into oriented lithium hectorite (LiHT) films. R6G and oxazine 4 (Ox4) are typical laser dyes with similar condensed ring structures, their main difference being a bulky e
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