Derivatives of Bis(trifluoromethyl)biphenyl and Various Donor Noieties Exhibiting Dual State Emission

Abstract

A series of bis(trifluoromethyl)biphenyl derivatives bearing carbazole, dimethylacridan, and phenothiazine donor moieties were designed and synthesized via Ullman coupling reaction. The compounds were found to be capable of forming molecular glasses with glass transition temperatures ranging from 152 °C to 244 °C. Significant dual-state emission was revealed for the synthesized compounds. Radiative decay of singlet and triplet states emerged from restricted molecular motion in solid state. The phenothiazinyl-substituted bis(trifluoromethyl)biphenyl derivative induces particular interest, as it exhibits room-temperature phosphorescence. This makes it promising for oxygen sensing applications. The theoretical work revealed that carbazolyl disubstituted bis(trifluoromethyl)biphenyl has the largest deviation of the planes of donor and acceptor fragments from 90°, which leads to larger overlap of electron density in the ground and excited states and larger oscillator strength. The calculated values of dipole moment and charge transfer during excitation were found to be the lowest for phenothiazinyl disubstituted bis(trifluoromethyl)biphenyl. This result explains the experimental fact that the solvent polarity has the least effect on the fluorescent spectrum of this compound.