Spectroscopy and dynamics of DCM encapsulated in MCM-41 and Y zeolite mesoporous materials

The laser dye 4-(dicyanomethylene)-2-methyl-6-( p-dimethylaminostyryl)-4H-pyran (referred to as DCM) was encapsulated in mesoporous MCM-41 and Y-zeolite. The resultant composites were studied by X-ray diffraction, UV-Vis absorption and emission spectroscopies, and fluorescence lifetime spectrophometry at room temperature. The interactions between occluded DCM and the internal surfaces of the porous materials are found to modify the optical spectra and dynamics of the confined DCM molecules. In particular, two fluorescence bands are observed for DCM occluded within MCM-41, while one fluorescence band is observed for DCM occluded within Y-zeolite or dissolved in DMSO. The dual bands are attributed to emissions from the lowest excited (LE) state and a state created as a result of intramolecular charge transfer, specifically, the twisted intramolecular charge transfer (TICT) state. The decay lifetimes for the LE and TICT states are found to be 0.6 ^ 0.1 and 1.9 ^ 0.1 ns, respectively, with 480 nm excitation; the decay lifetimes for 514 excitation are essentially the same. The single emissions from the DCM/Y-zeolite composite and the homogeneous DMSO solution show single exponential decays with lifetimes of 1.3 ^ 0.1 and 2.0 ^ 0.1 ns, respectively, both assigned to the TICT state. q 2004 Elsevier B.V. All rights reserved.