Dye in nanochannels boosts performance of artificial photonic antenna systems

Abstract

Materials that absorb all light in the right wavelength range and transfer the electronic excitation energy via fluorescenceresonance energy transfer (FRET) to well-organized acceptors offer unique potential for developing dye-sensitized solar cells, luminescent solar concentrators (LSCs), and color-changing media (used, for example, in sensing devices). We have succeeded in producing artificial photonic-antenna systems by incorporating dyes into a nanoporous material.1–3 The material we chose was zeolite L, as it has proven an ideal host. Its crystals are cylindrically shaped porous aluminosilicates featuring hexagonal symmetry. The size and aspect ratio of the crystallites can be tuned over a wide range. A nanometer-sized zeolite-L crystal consists of many thousands of 1D channels oriented parallel to the cylinder axis. These can be filled with suitable ‘guest’ molecules (see Figure 1). Geometrical constraints imposed by the host structure lead to supramolecular organization of the guests. Thus, very high concentrations of nonor only very weakly interacting dye molecules can be reached. The channel openings are plugged with a second type of fluorescent dye, called stopcock. The two types of molecules are precisely tuned to each other. The stopcocks accept excitation energy from the dyes in the channels, but cannot pass it back. The supramolecular organization of dyes in the zeolite allows light harvesting within the volume of a dye-loaded zeoliteL crystal and radiationless energy transport to the cylinder ends. The second stage of organization involves the coupling to an external acceptor stopcock at the ends of the zeolite-L channels, which can then trap electronic excitation energy. The third stage of organization is attained by interfacing the maFigure 1. Schematic overview of an artificial photonic antenna.1, 3 The chromophores are embedded in the channels of the host material. The green dyes act as donor molecules that absorb the incoming light and transport the electronic excitation energy via fluorescence-resonance energy transfer4 to the red acceptors shown at the ends of the channels on the right. The process can be analyzed by measuring the emission of the red acceptors and comparing it with that of the donors. (right) Top view of a bunch of such strictly parallel channels.