Amine quenching of fluorescence of phenylated anthracenes

New Insights into an Old Problem. Fluorescence Quenching of Sterically-Graded Pyrenes by Tertiary Aliphatic Amines

“…Consequently, in order to observe reasonable amounts of quenching, moderate to high concentrations of some amines (vide inf ra) were required, and they may have altered somewhat the polarity and other properties of the media. 34,35 By maintaining the same increments of quencher concentration changes throughout, the effects of any perturbations to the solvent systems on the quenching kinetics were kept virtually constant. Even in acetonitrile, a more polar solvent that can stabilize charge-transfer interactions more readily and at larger intermolecular distances than can a In trials 1 and 2, the sample orientations were at 45°and 65°angles, respectively, with respect to the incident excitation beam.…”

“…The more severe steric constraints affect the communication between PyOMe and the quencher; they are dependent upon the shape of the quencher and are manifested in the quenching rate constants ( k q ). Consequently, in order to observe reasonable amounts of quenching, moderate to high concentrations of some amines ( vide infra ) were required, and they may have altered somewhat the polarity and other properties of the media. , By maintaining the same increments of quencher concentration changes throughout, the effects of any perturbations to the solvent systems on the quenching kinetics were kept virtually constant. Even in acetonitrile, a more polar solvent that can stabilize charge-transfer interactions more readily and at larger intermolecular distances than can THF, , the quenching rate constant for tributylamine (444A), the least efficient quencher in THF, was more than an order of magnitude slower than the diffusion limit (Figure S8).…”

Fluorescence Quenching of n,π*-Excited Azoalkanes by Amines: What Is a Sterically Hindered Amine?

“…Significant steric effects on the kinetics of CT-induced quenching of ketones and quinones were observed for aromatic donors as quenchers. , It has been suggested, based on the comparison with structural data for the electron-donor−acceptor ground-state complexes of these donors, that steric effects on the kinetics are manifested in the hindrance toward formation of intermediate π-type sandwich exciplexes with aromatic quenchers. In earlier studies the steric demand of fluorescent acceptors was varied. − …”

“…In the present study, aliphatic amines were examined as sterically congested donors in CT-induced quenching. The donor properties of amines are of considerable practical interest for photoreduction of ketones, − azoalkanes, − and dyes, as well as in polymer technology, where amines serve both as photoinitiators and light stabilizers. , In addition, fluorescence quenching by amines has been the subject of numerous mechanistic investigations. ,,,− Obviously, aliphatic amines donate electrons through their lone pair orbital and are expected to interact with excited states in a different manner than aromatic donors. The absence of steric effects on quenching of benzophenone by amines was previously attributed to diffusion-controlled quenching, which could mask subtle steric effects.…”

Convenient Synthesis of Tetra- and Hexaarylanthracenes by Means of RuH2(CO)(PPh3)3-Catalyzed C−H Arylation of Anthraquinone with Arylboronates

“…Reduction of tetra( p -tolyl)anthraquinone 4a with aqueous HI and acetic acid at 140 °C in a sealed tube afforded 1,4,6,9-tetra( p -tolyl)anthracene ( 7 ) in 83% yield (eq ). , This result illustrates that the ruthenium-catalyzed tetraarylation of anthraquinone with arylboronates and the reduction with HI constitutes a convenient two-step procedure for the synthesis of tetraarylanthracenes …”