Design, Regioselective Synthesis, and Photophysical Properties of Perfluoronaphthalene-Based Donor-Acceptor-Donor Fluorescent Dyes

A one-step route to a series of perfluoronaphthalene-based donor (D)-acceptor (A)-D fluorescent dyes with various electron-donating groups was developed. The perfluoronaphthalene moiety in the D-A-D dyes served as a good electron-accepting aromatic ring with excellent intramolecular charge transfer properties, as determined by density functional theory calculations and measurements of the fluorescence properties in solution, in poly(methyl methacrylate) (PMMA) films, and in crystal form. Notably, replacing the naphthalene ring with perfluoronaphthalene in the D-A-D dyes carrying the phenothiazine moiety not only stabilized the highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels but also reduced the energy band gap to change the emission color from blue to yellow. Among the four synthesized perfluoronaphthalene D-A-D dyes, those bearing diphenylamino groups afforded the best fluorescence quantum yields in Et2O solution (0.60) and in PMMA film (0.65) because the propeller structure of the diphenylamino group that acts as a donor substituent effectively suppresses radiation-free deactivation. In contrast, in the crystalline state, the carbazoyl-bearing D-A-D dye provided the best fluorescence quantum yield (0.35) because the radiation-free inactivation was suppressed by pi-pi(F) stacking at the donor site, which was confirmed by single-crystal X-ray analysis.

Automated summary

A series of perfluoronaphthalene-based donor-acceptor-donor fluorescent dyes were successfully synthesized using a one-step route. The perfluoronaphthalene moiety served as a good electron-accepting aromatic ring with excellent intramolecular charge transfer properties. Replacing the naphthalene ring with perfluoronaphthalene stabilized the energy levels and reduced the energy band gap, leading to a change in the emission color. Among the synthesized dyes, those with diphenylamino groups showed the highest fluorescence quantum yields in solution and film, while the dye with carbazoyl group exhibited the highest fluorescence quantum yield in the crystalline state.