Zethrene and dibenzozethrene: masked biradical molecules?

The syntheses, structures, and physical properties of dibenzozethrenes were explored. The results thus obtained were compared with those for zethrenes. Dibenzozethrenes were synthesized by the nickel-catalyzed cyclodimerization of 9-ethynyl-1-iodoanthracenes. The substituents in zethrene and dibenzozethrene twisted their backbones, and remarkably influenced their properties. Unlike closed-shell disubstituted derivatives, the parent zethrene and dibenzozethrene are singlet open-shell biradicals, which were studied by variable-temperature (1)H NMR, ESR, SQUID and computational methods. Since substituents were observed to affect significantly the biradical properties, the relevant mechanisms were analyzed. The nonlinear optical performance of each of these compounds depends on its π-conjugation and biradical properties. Dibenzozethrenes have larger two-photon absorption cross-sections than zethrenes, as most strongly evidenced by the parent dibenzothrene [σ(max)=4323 GM at 530 nm].

Effect of bis-triazoles on a ribose-based fluorescent sensor.

We synthesized two ribosyl-based fluorescent sensors. Both sensors have an anthracene as the fluorophore, but they differ in the recognition site for metal ions. One (3) has two ribosyl esters, and the other (6) has two triazole groups linked to two ribosyl esters. Among the metal ions examined in MeOH, compound 3 displayed a large chelation-enhanced fluorescence (CHEF) effect with Hg(2+) and Cu(2+) ions, and compound 6 displayed a large chelation-quenched fluorescence (CHQF) effect with Cu(2+) and Ni(2+) ions. The results demonstrated that the absence (sensor 3) and presence (sensor 6) of an incorporated bis-triazole group in a ribosyl-based fluorescent sensor conferred different preferences and distinct binding modes for metal ions.