6. Rehybridization of the Acceptor (RICT) 3908 7. Planarization of the Molecule (PICT) 3909 III. Fluorescence Spectroscopy 3909 A. Solvent Effects and the Model Compounds 3909 1. Solvent Effects on the Spectra 3909 2. Steric Effects and Model Compounds 3911 3. Bandwidths 3913 4. Isoemissive Points 3914 B. Dipole Moments 3915 C. Radiative Rates and Transition Moments 3916 1. Quantum Yields and Radiationless Deactivation Processes 3916

Structural Changes Accompanying Intramolecular Electron Transfer: Focus on Twisted Intramolecular Charge-Transfer States and Structures

Azobenzene undergoes trans → cisisomerization when irradiated with light tuned to an appropriate wavelength. The reverse cis →transisomerization can be driven by light or occurs thermally in the dark. Azobenzene's photochromatic properties make it an ideal component of numerous molecular devices and functional materials. Despite the abundance of application-driven research, azobenzene photochemistry and the isomerization mechanism remain topics of investigation. Additional substituents on the azobenzene ring system change the spectroscopic properties and isomerization mechanism. This critical review details the studies completed to date on the 3 main classes of azobenzene derivatives. Understanding the differences in photochemistry, which originate from substitution, is imperative in exploiting azobenzene in the desired applications.

Photoisomerization in different classes of azobenzene

Reversible Photocontrol of Biological Systems by the Incorporation of Molecular Photoswitches

Fluorescent Dyes and Their Supramolecular Host/Guest Complexes with Macrocycles in Aqueous Solution Roy N. Dsouza, Uwe Pischel,* and Werner M. Nau* School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, D-28759 Bremen, Germany Centro de Investigaci on en Química Sostenible (CIQSO) and Departamento de Ingeniería Química, Química Física y Química Org anica, Universidad de Huelva, Campus de El Carmen s/n, E-21071 Huelva, Spain

Fluorescent dyes and their supramolecular host/guest complexes with macrocycles in aqueous solution.

This chapter overviews molecular machines based on cyclodextrins (CDs). The categories of CD-based molecular machines, external stimuli for CD-based molecular machines, and typical examples of CD-based molecular machines are briefly described.

Cyclodextrin-based molecular machines

Cis-trans photoisomerization of azobenzene. Solvent and triplet donors effects

cis .dblharw. trans Photoisomerization of azobenzene-cyclodextrin inclusion complexes

The cis → trans photoisomerization of azobenzene: an experimental re-examination

Photochemistry in Cyclodextrin Cavities

The photochemistry of 3- and 4-benzoylpyridine-cyclodextrin inclusion complexes (BPyCDx) was examined by nanosecond laser flash-photolysis and stationary techniques. The lifetimes of the triplet complex and of the triplet radical pair, formed by H-abstraction from a glucose unit of the CDx, have been measured in β-CDx complexes. The reactivity of the heterocyclic ketones with CDx is higher than that of benzophenone, but the lower binding ability of the macrocycle toward these more hydrophylic molecules induces faster separation of the geminate radicals. The quantum yields of the escaped radicals and their decay kinetics have been determined. The β-CDx cage favours geminate recombination reactions, while α- and -γ-CDx tend to release the guest molecule. Cage products have been spectroscopically characterized in the case of the 3-BPy-β-CDx system.

Pietro Bortolus

Papers

Cis-trans photoisomerization of azobenzene. Solvent and triplet donors effects

cis .dblharw. trans Photoisomerization of azobenzene-cyclodextrin inclusion complexes

The cis → trans photoisomerization of azobenzene: an experimental re-examination

Photochemistry in Cyclodextrin Cavities

PHOTOCHEMISTRY IN A CYCLODEXTRIN CAVITY. PRIMARY PROCESSES IN THE PHOTOREDUCTION OF 3- and 4-BENZOYLPYRIDINE STUDIED BY LASER FLASH-PHOTOLYSIS*