Microwave-assisted solid state intercalation of Rhodamine B and polycarbazole in bentonite clay interlayer space: structural characterization and photophysics of double intercalation

Abstract

Intercalation of organic moieties in layered double hydroxides/clays has been used to obtain various hybrid compounds with enhanced properties and wide ranging applications. Most intercalation of organic moieties into clays is performed in aqueous media through the mechanism of ion exchange. However, intercalation of organic moieties in clays can also occur through diffusion in the solid state if the process is carried out under microwave irradiation. We have attempted in this study to investigate, for the first time, the double intercalation of two organic moieties, Rhodamine B and polycarbazole, in bentonite clay galleries in the solid state through microwave irradiation at controlled temperatures of 30 °C and 50 °C. Polycarbazole was simultaneously polymerized from carbazole under the above experimental conditions. Optical micrography revealed the intercalation of both Rhodamine B and polycarbazole. Carbon, hydrogen, and nitrogen (CHN) analysis quantitatively indicated the intercalated amounts of the two moieties. X-ray diffraction analysis showed the orientations of the Rhodamine B and polycarbazole molecules and how the higher loading of Rhodamine B and polycarbazole distorts the lattice of the bentonite clay. Confocal microscopy distinctly showed the presence of both Rhodamine B and polycarbazole in the interlayer space. Quantum yield (Φ) values more explicitly demonstrated the effect of increasing the amounts of Rhodamine B and polycarbazole in the clay galleries. The fluorescence lifetimes (τ_f), intrinsic fluorescence decay constants (k^°_f) and internal conversion constants (k_IC) showed consistent and distinct values for the double intercalation variables. The symmetrical configuration of Rhodamine B molecules was deformed by distortion of the dihedral angles of the pendant phenylene and carboxylate groups in the clay galleries. These distortions created fluorescence states with different decay times and energies.