Synthesis, Characterization and Properties of Electron Donor-Acceptor Complexes Based on 9,9-Diarylfluorene

Abstract

A series of fluorene-triphenylamine derivatives containing an electron donor-acceptor (D-A) structure based on 9,9-diarylfluorene was designed and synthesized. Their optical properties were investigated by UV-Vis spectroscopy and photoluminescence (PL) techniques in solution as well as in the solid state. The maximum PL emission wavelengths of the compounds ranged from 430 to 530 nm. A dual fluorescence phenomenon was observed in particular polar solvents and the relationship between emission properties and molecular structures was studied. The results reveal the existence of a charge transfer (CT) excited state in the molecules and the PL properties of these compounds depend on the structure of the compound and also on the polarity of the solvent. The molecular constitution of the compounds improves the hole-injection issues for fluorene-based materials because of the introduction of a triphenylamine group. Cyclic voltammetry (CV) shows that the highest occupied molecular orbital (HOMO) energy level of the compounds is located between -5.24 and -5.50 eV and it can be tailored by changing the electronegativity of the substituent group. Simultaneously, the spiro-skeleton molecular structure leads to an excellent glass transition temperature (192-206 °C) and it retains good morphological stability. The thermogravimetric (TG) curves of the compounds show a thermal-decomposition temperature of higher than 400 °C.