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.

The synthesis and characterization of dye loaded zeolite L sandwiches acting as artificial antenna systems for light harvesting and transport is reported. A set of experimental tools for the preparation of neutral dye-zeolite L materials ranging from low to maximum packing densities has been developed. The role of co-adsorbed water and the distribution of molecules between the inner and the outer surface were found to be the determining parameters. p-Terphenyl (pTP) turned out to be very suitable for studying these and other relevant parameters of neutral dye-zeolite L materials. We observed that pTP located in the channels of zeolite L can reversibly be displaced by water. This can be used when synthesizing such materials. We also observed that all-trans-1,6-diphenyl-1,3,5-hexatriene (DPH) which is very photolabile in solution is stable after insertion into zeolite L. By combining our extensive knowledge of these systems with ionexchange procedures developed in an earlier study, we have realized the first bi-directional three-dye antenna. In this material the near UV absorbing compounds DPH or 1,2-bis-(5-methyl-benzoxazol-2-yl)-ethene (MBOXE) are located in the middle part of zeolite L nanocrystals followed on both sides by pyronine (Py) and then by oxonine (Ox) as acceptors. Fluorescence of the oxonine located at both ends of the cylindrical zeolite L crystals was observed upon excitation of the near UV absorber in the middle section at 353 nm, where neither oxonine nor pyronine absorb a significant amount of the excitation light.

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