Synthesis and Luminescence Properties of U-Shaped Polycyclic Molecules Containing Syn-Facial Functionalized Quinoxaline Rings

Abstract

[reaction: see text] Rigid U-shaped molecules containing syn-facially situated quinoxaline rings have been synthesized in three steps, by a combination of the Diels-Alder reaction, the ruthenium-catalyzed oxidation, and the Zn(OAc)(2)-catalyzed condensation of the resulting bis-alpha-diketones with benzene-1,2-diamines. The unsymmetric bis-quinoxalines, with electronically different substituents, and the quinoxaline ring-attached alpha-diketones were also prepared. Their luminescence properties were examined and described.

Preparation, structures and preliminary host–guest studies of fluorinated syn-bis-quinoxaline molecular tweezers

“…The general route [19] to bis-quinoxaline targets (Scheme 2) utilizes a twofold Diels–Alder reaction of a cycloalkadiene ( 5 , 6 ) with cyclopentadienone derivatives ( 7 ), subsequent oxidation of the syn -diene intermediates ( 8 , 9 ) to their corresponding tetraketones ( 10 , 11 ) and condensation of the latter with o -phenylenediamine derivatives ( 12 ) to obtain the syn -bis-quinoxaline target compounds ( 15 , 16 ). This synthetic route is flexible with regard to the tether size (cyclohexane vs cyclooctane) and modifications in the pincer sidewalls (degree of fluorination).…”

“…Their full characterization and some preliminary host–guest studies of the cyclooctadiene-derived frameworks could however, be carried out in dilute chloroform, acetonitrile and methylene chloride solutions. The spectroscopic characteristics of 15a and several non-fluorinated derivatives have been described elsewhere [19] and the NMR spectroscopic data for 15b – c ( 16a – d ) are only altered by the absence of the corresponding proton resonances, the additional coupling of fluorine with either the arene protons in 15c ( 16c ) or the aromatic carbon atoms, and the more complex signal structure of the spirocyclic ketal in 16a – d . The UV–vis spectra (available in the Supporting Information File 1) display the expected electronic transitions for quinoxaline derivatives [33–35], i.e., a prominent π,π* transition with λ max between 236–245 nm and a lower intensity n ,π* transition with λ max between 312–316 nm with a poorly resolved vibrational structure.…”

“…Intrigued by Chou’s communication on the spectroscopic properties of non-fluorinated bis-quinoxalines of type 3 and 4a [19], we targeted on the corresponding fluorinated derivatives – in particular compound 4b with its large binding cleft.…”

Synthesis and molecular assembly of benzenoid ring-mounted U-shaped septuple-bridged [7,7]orthocyclophanes walled by cofacial quinoxaline rings

“…33e35, 39,40 X-ray crystallographic analysis revealed that the pair of QX sidewalls in orthocyclophanes 1 (A) are stretching out from the rigid spacer scaffold in almost parallel (syn-periplanar) manner, separated by centroid-to-centroid distances of about 7.5e8.5 A. 33,34 These distances are too distant to exhibit excimer or exciplex emission via the intramolecular pep interaction. Such a photophysical phenomenon was displayed by the U-shaped quadruple-bridged [5,5] orthocyclophanes, wherein the aromatic sidewalls are separated by about 4.0e4.5 A.…”

“…Such a photophysical phenomenon was displayed by the U-shaped quadruple-bridged [5,5] orthocyclophanes, wherein the aromatic sidewalls are separated by about 4.0e4.5 A. 33,39,40 On the other hand, orthocyclophanes 1 (A) could belong to a family of molecules termed molecular clefts 18,19 due to their concaveeconvex topography with rim-to-rim distances of 7.5e8.5 A that are suitable to form complexes with molecular substrates by clipping the substrate via pep stacking interactions. 34,39 In all crystal structures of orthocyclophanes 1, V-shaped dimeric entities resulting from reciprocal clipping of the aromatic sidewalls of two molecules of 1 into the opposing U-shaped cleft by angles ranging from 45 to 85 were observed.…”