2019 Volume 77 Issue 8 Pages 823-830
17H-Tetrabenzo [a, c, g, i] fluorene (TBF) as one of π-extended fluorene derivatives was first prepared about 60 years ago. Although π-extended fluorenes have been received vast attention from the field of organic electronics, TBF derivatives have not been well explored from the physicochemical points of view. Six 17,17- dialkylTBFs (methyl to n-hexyl) prepared from TBF show intense blue fluorescence in solutions. On the other hand, in the solid state, the fluorescent spectra and the quantum yields (ΦSD) vary with their alkyl chains. In particular, the ΦSD values of dialkylTBFs bearing n-propyl to n-hexyl groups are close to unity, while the fluorescence of parent TBF is almost quenched. Crystallographic analyses revealed that the π-π interactions of the TBF moieties probably play an important role in quenching the solid-state fluorescence. Quinone methide, and unsymmetrical and symmetrical fulvalene involving a TBF unit were synthesized. The electrochemical analyses reveal that these compounds exhibit high electron affinities. The substituent effect on optical properties of 3,14-diphenyl-17,17-di(n-pentyl)TBF derivatives bearing various substituents (H, CN, COOCH3, CHO, NO2, CH=C(CN)2) at 4-position of the phenyl groups were also synthesized and characterized. The diformyl, dinitro, and bis(dicyanoethenyl) derivatives show large solvatofluorochromism (CHO; ΔλFL=67 nm, NO2; ΔλFL=96 nm, CH=C(CN)2; ΔλFL=170 nm). Moreover, the diformyl derivative exhibits crystallochromism in fluorescence, and the dinitro and bis(dicyanoethenyl) derivatives display aggregation induced emission. The bis(dicyanoethenyl) derivative can also serve as a highly sensitive fluorescence “turn-on” probe for cyanide ion. The findings suggest that the ground-to-excited state electronic transition of these compounds should have intramolecular charge-transfer (ICT) character.
