Synthesis, computational, and photophysical characterization of diaza-embedded [4]helicenes and pseudo[4]helicenes and their pyridinium and viologen homologues

Abstract

Synthesis of three [4]heli-viologens and their helical precursors, and two "pseudo-[4]helicenes" and their alkylated derivatives, which have potential device and catalysis applications, are reported. Their structures and racemization barriers have been explored with the B3LYP/6-311+G(2d,p), M06-2X/6-311+G(2d,p), and M11/6-311+G(2d,p) computational models. The photophysical properties of the helicenes and pseudo-helicenes and their alkylated derivatives have been measured. Unusual singlet-triplet energy gaps, EST, were measured and discussed for the charged alkylation products.

Novel functional [4]helicenes through a photooxidation pathway. Investigation of the absorption and fluorescence in solution

“…(E g−opt ) of each [4]helicene was calculated from the absorption onset and was found to be 3.07 to 3.31 eV (Tables 5 and 6). Their UV profiles resembled those of some tetracyclic systems having interesting photophysical properties [42][43][44].…”

New [4]helicene derivatives: Synthesis, characterization and photophysical properties

“…with maxima at 289-320 nm that could be assigned to   and n electronic transitions. The optical band gap values of theses systems appear to be lower than optical gap of 2-methyl-8,9-diaza [4]helicene (Eg-op = 3.25 eV) [40] and comparable to that of pyrenecored [4]helicenes which might be promising candidates in organic light-emitting devices (OLEDs) [14].…”

“…Their photophysical and chiroptical properties have been also investigated [21][22][23][24][25]. The [4]helicene skeleton demonstrate various applications such as molecular motor, building blocks for highly conjugated structures as well as larger [n]helicenes that have proved successful as chiral catalysts and ligands in asymmetric synthesis [26][27][28][29][30][31][32][33] and as blue emitters in OLEDs [34][35].…”

Pyridoacridines in the 21st Century

“…In the 21 st century, the ring system has been produced incidentally in studies of helical substances in the context of supramolecular chemistry and catalysis – various [5]heli‐viologen isomers were produced by quaternisations . The construction of precursors 247 for photochemical cyclisations was achieved with a Hiyama–Heck coupling of a 3‐bromoquinoline and vinyltriethoxysilane.…”