The focus of this research is on host-guest composites with photonicantenna properties. The material generally consists of cylindrical zeoliteL crystals, the channels of which are filled with dye molecules. Size andmorphology of the crystals can be tuned from 30 nm to 6000 nm and fromelongated to flat shape, respectively. The synthesis of the composites isbased on the fact that molecules can diffuse into individual channels,either from the gas phase at elevated temperature or under ion exchangeconditions, depending on the properties of the dyes. This means that, inprinciple, they can also leave the zeolite by the same way. In some cases,however, it is desirable to block their way out by adding a closuremolecule. Functionalization of the closure molecules allows tuning of, forexample, wettability, refractive index, and chemical reactivity. Thesupramolecular organization of the dyes inside the channels is a firststage of organization. It allows light harvesting within a certain volumeof a dye-loaded nanocrystalline zeolite and radiationless transport toboth ends of the cylinder or from the ends to the center. The second stageof organization is the coupling to an external acceptor or donor stopcockfluorophore at the ends of the zeolite L channels, which can trap orinject electronic excitation energy. The third stage of organization isthe coupling to an external device via a stopcock intermediate. Thewide-ranging tunability of these highly organized materials offersfascinating new possibilities for exploring excitation energy transferphenomena.
T. Ban, D. Brühwiler, G. Calzaferri
Selective modification of the channel entrances of zeolite L withtriethoxysilylated coumarin
J. Physical Chemistry B 2004, in press
S. Huber, G. Calzaferri
Sequential Functionalization of the Channel Entrances of Zeolite LCrystals
Angew. Chem. Int. Ed. 2004, in press
Two functionalization principles of the channels will be further explored.One of them is based on specific reactions with OH-groups at the end andthe entrance of the channels. The other is based on electrostaticinteractions.
Channel end functionalization (stopcock principle) is the basis for thesecond and third stage of organization (it can also be very useful forimproving the well mastered first stage materials) and for the preparationof photoactive stopcock switches (magnetic, cis-trans, complex equilibria,etc.) with largely amplified sensitivity due to the antenna function ofthe dye-loaded zeolite.
Orientation, organization, and fixation of micro- and nanosized crystalson a substrate is the basis for the preparation of optically highlyanisotropic and of unidirectional materials, both of which will beexplored by electronic absorption, luminescence, and vibrationalspectroscopy (IR, Raman).
The mechanism of electronic excitation energy transfer and migration inthe highly organized crystals/materials/monolayers will be furtherexplored. The creation of electron hole pairs by energy transfer from theantenna via the stopcock to the semiconductor will be explored by means ofluminescence spectroscopy.