Vibronic Intramolecular Resonant Energy Transfer along More than 5 nm: Synthesis of Dyads for a Re-Examination of the Distance Function of FRET.

Dyads of chromophores with orthogonal transition moments and sequences of aliphatic cage-structures as spacers were prepared where resonance energy transfer (FRET) proceeded in contrast to Förster's theory even until 58 Å. The distance dependence of the efficiency was re-examined by means of various functions; the commonly used R-6 dependence gave acceptable results, but a slightly larger exponent was more useful for practical applications.

OrthoFRET in Diamantane FRET in Orthogonal Stiff Dyads; Diamond Restriction for Frozen Vibrations.

Energy transfer proceeds in orthogonal dyads in contrast to Förster's theory and cannot be prohibited even by rigid interconnecting cage compounds such as cubane or diamantane.

Switch-On Fluorescence of a Perylene-Dye-Functionalized Metal-Organic Framework through Postsynthetic Modification.

A perylene dye was introduced directly as a linker into a metal-organic framework (MOF) during synthesis. Depending on the dye concentration in the MOF synthesis mixture, different fluorescent materials were generated. The successful incorporation of the dye was proven by using (13) C and (27) Al MAS NMR spectroscopy, by solution NMR spectroscopy after digestion of the MOF sample, and by synthesizing a reference dye without connecting groups, which could coordinate on the metal-oxo cluster inside the MOF. Fluorescence quenching effects of the MOF linker, 2-aminoterephthalate, were observed and overcome by postsynthetic modification with acetic anhydride. We show here for the first time that amino groups, which can be used as anchoring points for covalent attachment of other molecules, are responsible for fluorescence quenching. Thus, a very promising strategy to implement switchable fluorescence into MOFs is shown here.

Synthesis and reactivity studies of a tin(II) corrole complex.

A series of tris(pentafluorophenyl)corrole (TPFC) tin(IV) and tin(II) complexes were prepared and studied by various characterization techniques including (1)H, (19)F, and (119)Sn NMR and UV-vis spectroscopy, mass spectrometry, and single-crystal X-ray diffraction. The unusual 4-coordinate, monomeric, divalent tin(II) complex [(TPFC)Sn(II)](-) (2a) showed highly efficient reactivity toward alkenes and alkyl halides via a nucleophilic addition pathway leading to the quantitative formation of alkyl stannyl corrole compounds. DFT calculations confirmed the divalent nature of the tin center in 2a, and an NBO analysis showed about 99.99% Sn lone pair character, of which 83.6% was Sn 5s and 16.35% was Sn 5p character.

How many molecular layers of polar solvent molecules control chemistry? The concept of compensating dipoles.

The extension of the solvent influence of the shell into the volume of a polar medium was examined by means of anti-collinear dipoles on the basis of the E(T)(30) solvent polarity scale (i.e., the molar energy of excitation of a pyridinium-N-phenolatebetaine dye; generally: E(T) =28,591 nm kcal mol(-1)/λmax) where no compensation effects were found. As a consequence, solvent polarity effects are concentrated to a very thin layer of a few thousand picometres around the solute where extensions into the bulk solvent become unimportant. A parallelism to the thin surface layer of water to the gas phase is discussed.

Noncovalent control of absorption and fluorescence spectra.

Perylene dyes with N-tert-alkyl substituents were prepared in which noncovalent interactions of the crowded substituent cause a variation of the geometry of the core and induce hypsochromic shifts in absorption and fluorescence. The interpretation of the shifts was supported by means of DFT calculations and an X-ray crystal structure analysis.

Turn-on fluorescence triggered by selective internal dye replacement in MOFs.

Coordinatively unsaturated metal sites (CUS) are used to create dye-functionalized metal-organic frameworks (MOFs). The quenching of dye fluorescence through interactions with the CUS can be utilised for chemical sensing of Lewis bases that displace the dye from the CUS, resulting in a triggered turn-on fluorescence signal.