The focus of this review is on host-guest composites with photonic antenna properties. The material generally consists of cylindrical zeolite L crystals the channels of which are filled with dye molecules. The synthesis is based on the fact that molecules can diffuse into individual channels. This means that, under the appropriate conditions, 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 closure molecule. Functionalization of the closure molecules allows tuning of, for example, wettability, refractive index, and chemical reactivity. The supramolecular organization of the dyes inside the channels is a first stage of organization. It allows light harvesting within a certain volume of a dye-loaded nanocrystalline zeolite and radiationless transport to both ends of the cylinder or from the ends to the center. The second stage of organization is the coupling to an external acceptor or donor stopcock fluorophore at the ends of the channels, which can trap or inject electronic excitation energy. The third stage of organization is the coupling to an external device through a stopcock molecule. The wide-ranging tunability of these highly organized materials offers fascinating new possibilities for exploring excitation-energy-transfer phenomena, and challenges for developing new photonic devices.

Monolayers of a series of 1-alkynes, from 1-dodecyne to 1-octadecyne, have been prepared on the hydrogen-terminated Si(100) surface via a thermal reaction of the organic compound with this Si surface. An efficient procedure is presented for the synthesis of 1-alkynes from the corresponding 1-alkenes. The resulting monolayers were characterized by water contact angle measurements, ATR infrared spectroscopy, and X-ray reflectivity. The results show that these 1-alkynes give well-ordered, covalently bonded monolayers, which are at least as ordered as those of the corresponding 1-alkenes. The exact binding geometry of the 1-alkyne to the Si surface was investigated. The results from IR spectroscopy and X-ray reflectivity measurements indicate that the 1-alkynes form two Si−C bonds to the surface per reacting molecule. Quantum mechanical calculations confirm that this formation of two Si−C bonds is not only chemically possible but also energetically much more favorable than formation of only one Si−C bond per reacting molecule.

The photoisomerization of the push-pull substituted azo dye Disperse Red 1 is studied using femtosecond time-resolved absorption spectroscopy and other spectroscopic and computational techniques. In comparison with azobenzene, the pipi* state is more stabilized by the effects of push-pull substitution than the npi* state, but the latter is probably still the lowest in energy. This conclusion is based on the kinetics, anisotropy of the excited state absorption spectrum, the spectra of the ground states, and quantum chemical calculations. The S(1)(npi*) state is formed from the initially excited pipi* state in <0.2 ps, and decays to the ground state with time constants of 0.9 ps in toluene, 0.5 ps in acetonitrile, and 1.4 ps in ethylene glycol. Thermal isomerization transforms the Z isomer produced to the more stable E isomer with time constants of 29 s (toluene), 28 ms (acetonitrile), and 2.7 ms (ethylene glycol). The pathway of photoisomerization is likely to be rotation about the N=N bond. Quantum chemical calculations indicate that along the inversion pathway ground and excited state energy surfaces remain well separated, whereas rotation leads to a region where conical intersections can occur. For the ground-state Z to E isomerization, conclusive evidence is lacking, but inversion is more probably the favored pathway in the push-pull substituted systems than in the parent azobenzene.

Wir stellen Wirt‐Gast‐Materialien vor, aufgebaut aus zylindrischen Zeolith‐L‐Kristallen, deren Kanäle mit Farbstoffmolekülen gefüllt sind. Die Synthese dieser Stoffe beruht auf der Eigenschaft der Moleküle, in einzelne Kanäle zu diffundieren. Der umgekehrte Prozess, das Herausdiffundieren der Farbstoffe, kann mithilfe eines molekularen “Korkens” unterdrückt werden. Durch Funktionalisierung dieser zapfenförmigen Moleküle lassen sich Eigenschaften wie Benetzbarkeit, Brechungsindex und chemische Reaktivität einstellen. Die supramolekulare Organisation der Farbstoffe innerhalb der Kanäle entspricht einer ersten Organisationsstufe. Damit gelingt es, Licht im Volumen eines Nanokristalls zu sammeln und Anregungsenergie strahlungslos an die Enden des Zylinders oder umgekehrt von dort zur Mitte zu transportieren. Eine zweite Organisationsstufe ist die Kupplung an einen externen Acceptor‐ oder Donor‐Zapfenfluorophor an den Kanalenden, der elektronische Anregungsenergie abfängt oder einspeist. Die dritte, zum Teil noch hypothetische Stufe umfasst die Kupplung an eine externe Funktionseinheit über Zapfenmoleküle. Die Abstimmbarkeit dieser hochorganisierten Materialien bietet attraktive Möglichkeiten zur Untersuchung von elektronischen Energieübertragungsphänomenen und zur Entwicklung von neuen photonischen Funktionseinheiten.

Dedicated to Professor Roald Hoffmann on the occasion of his 65th birthdayMaterials which embed organic dyes, rare earth ions, complexes, or quantum dots in a matrix with specifically tailored chemical and optical properties provide a challenging approach to novel chemical and optical applications. These materials have the potential to be used in microoptics, optoelectronics, laser materials, solar cells, sensors, battery electrodes, and photocatalysis. In this article we focus on lanthanides encapsulated in zeolites, glass films derived from sol ± gel processes, and semiconductors.The research work on the unique luminescent properties of rare earth elements hosted in different matrixes is strongly motivated by their technological importance in optoelectronic devices. [1] The materials emit over the entire spectral range of interest: near infrared (NIR; Nd 3 , Er 3 ), red (Eu 3 , Pr 3 , Sm 3 ), green (Er 3 , Tb 3 ), and blue (Tm 3 , Ce 3 ). Their optical transitions involve 4f orbitals, which are well shielded from their chemical environment by 5s 2 and 5p 6 electrons. The f-f transitions are parity forbidden and, as a result, the absorption coefficients are very low and the emissive rates are slow, which results in long-lived and linelike emission bands. As a consequence, direct excitation of the lanthanide ions is unfavorable. The comparatively fast thermal relaxation of the excitation energy is a problem when using lanthanide ions for luminescence. This nonradiative relaxation may occur by interaction of the electronic levels of the lanthanide ion with suitable vibrational modes of the environment. [2] The efficiency of these processes depends on the energy gap between the ground and excited states as well as the vibrational energy of the oscillators. For example, when solvents containing OH groups are coordinated to lanthanide ions, efficient nonradiative deactivations take place through vibronic coupling with the vibrational states of the OH oscillators. Replacement of the OH oscillators by low-frequency OD oscillators, diminishes the vibronic deactivation pathway. [3] Different ways to overcome the difficulties of low absorptivity and thermal relaxation have been used. We show the apparently most important ones in Figure 1: a) matrix excitation followed by energy transfer to the lanthanide ion, b) ligand !metal charge transfer followed by lanthanide f-f emission, and c) ligand-centered absorption followed by energy transfer to the lanthanide ion.We first discuss the use of coordinating ligands as sensitizers. After absorption of light by the ligands, the electronic excitation energy is transferred and results in a luminescence of the lanthanide ion (see Figure 1 c). A possibility, given by Vˆgtle, Balzani, and co-workers, is to use a specially designed dendrimer which is able to play the role of the ligand for the lanthanide ions but which is also capable of working as an [*] Prof. Figure 1. Three paths to efficient lanthanide luminescence (ET energy transfer; REE rare earth emission; LMCT ligand !metal ch...