Orientation of Fluorescent Dyes in the Nano Channels of Zeolite L

Abstract

The orientation of the S 1 r S 0 π,π* transition dipole moments of oxonine (Ox + ), pyronine (Py + ), and POPOP (5,5′-diphenyl-2,2′-p-phenylenebis(oxazole)) in the channels of zeolite L crystals was investigated by means of fluorescence microscopy and single-crystal imaging. Qualitative observations led to the result that the transition moment of POPOP is aligned along the c-axis of the hexagonal crystals whereas the fluorescence of Ox + and Py + is not. More detailed investigations on Ox + showed a cone-shaped distribution of the transition moments with a half-cone angle of 72°. The orientation of the transition dipole moment for all of these molecules is parallel to the molecules' long axis. We found by means of space-filling arguments that POPOP, the van der Waals length of which is about 21 Å, can only be aligned along the channel axis. This is in full agreement with the observed fluorescence anisotropy. For Ox + and Py + , geometrical arguments based on the zeolite L structure give room for only two possible arrangements of the molecules' long axis: a half cone angle of up to 40°for Ox + and up to 30°for Py + , and an angle of about 90°for both of them with respect to the c-axis of zeolite L. The surprising discrepancy between geometrical considerations and the results of the fluorescence measurements can be explained by assuming that Ox + and Py + are exposed to a considerable anisotropic electrical field in the zeolite channels.

Microcontact Transfer Printing of Zeolite Monolayers

“…In fact, it is known that, due to the confinement in the channels, the larger dyes will be frozen in a certain orientation within the channels and their electronic transition moments will also show a fixed orientation. [29] We have therefore decided to explore the possibilities of creating patterned stripes that have different emission colors by changing the polarization of the excitation light. To achieve this goal, we filled the zeolites with two different dyes possessing perpendicular electronic transition moments once entrapped in the channels.…”

Quantum Yield Measurement of Fluorescent Zeolite Nanopigments

“…[27], thus proving that the transition moments of the perylene molecules are aligned in the onedimensional channels of the zeolite crystals [33]. We note that, if the perylene molecules were adsorbed at the zeolite surface instead of inside the zeolite channels, no evidence of emission anisotropy would be found in the fluorescence images [27,33]. Nevertheless, we acknowledge that the physical-chemical mechanisms enabling the insertion of large molecules, such as PDB, into the channels of zeolite L nanocrystals need to be further investigated.…”

Multimode microscopy: spectral and lifetime imaging

“…Zeolite L has a crystalline structure with internal sub-nanometre channels running through the crystal. Zeolite L assemblies are suitable hosts for fluorescent dyes (Megelski et al 2001;Maas et al 2003;Huber et al 2007). The fluorescent dye pyronine has been shown to intercalate into zeolite L crystals in a way that the individual dye molecules are aligned at defined angles within the crystal channels (Megelski et al 2001).…”