Synthesis and photophysical characterization of heterocyclic dihydrotetracenes and their utility in the fluorescence imaging of HeLa cells

Aza- and oxa-dihydrotetracenes were prepared in one step from 1,4-dicyanodibenzodioxins in good yields. These molecules represent the first examples of heterocyclic dihydrotetracenes with push-pull character. Aza-dihydrotetracene 18H showed a strong red-shifted absorbance maxima at 472 nm, nearly equal in intensity to the parent band at 260 nm, in polar DMSO medium. The fluorescence emission spectrum of aza-dihydrotetracene 18H had an emission maximum at 525 nm with a broad band stretched out as far as 650 nm. The fluorescence emission quantum yield was almost as strong as the known fluorescent standard 1,3-diphenylisobenzofuran. The aza-dihydrotetracenes exhibited in vitro cytotoxicity against the HeLa cell line and were non-toxic against the normal HaCaT cell line. The fluorescence emerging from HeLa cells incubated with aza-dihydrotetracene 18H was very strong and helped detect the cells microscopically using appropriate filters. (C) 2018 Elsevier Ltd. All rights reserved.