Novel π-extended hybrid xanthene dyes with two spirolactone rings for optoelectronic and biological applications.

The design, synthesis, and photophysical properties of organic fluorophores have attracted considerable research interest due to the utility of these compounds for various optoelectronic, analytical, and biological applications. In this study, we synthesized two novel π-extended red-emitting hybrid xanthene dyes, each of which has two spirolactone rings and combines a seminaphthofluorescein moiety and a seminaphthorhodafluor moiety in a single molecule. The photophysical properties of the dyes in methanol in the presence of acid, base, and metal cations were investigated. Mono-ring-opened seminaphthofluorescein and seminaphthorhodafluor forms of the dyes could be obtained by the addition of OH- or H+, respectively. Owing to the changes in the absorbance spectra of the mono-ring-opened forms induced by addition of H+ and OH-, the dyes could perform simultaneously the functions of an XOR gate and an INHIBIT gate, with the absorbances at 510 and 560 nm as outputs, respectively, and could act as half-subtractors with H+ and OH- as inputs. Furthermore, stepwise ring-opening could be induced by Hg2+ ions in methanol. In water, the dyes existed in double-ring-opened forms that emitted deep-red fluorescence and were mitochondria-targetable, suggesting that these chromophores might be useful as fluorescence tracers in biological applications. Because the absorption and fluorescence properties of these fluorophores can be regulated via their two spirolactone rings, we expect that these compounds will find utility in various optoelectronic, analytical, and biological applications.