Synthesis, structure and spectral properties of 9-diarylamino-substituted acridines

• Three 9-(diphenylamine)acridine dyes of the donor–acceptor type were synthesized.
• The acceptor and donor fragments are close to perpendicularity in the neutral forms of the dyes.
• The fluorescence bands of the dyes are red-shifted as compared to other known 9-aminoaryl-substituted acridines.
• The synthesized dyes exhibit a significant solvatofluorochromic effect and can be used as fluorescent chemosensors.
• Structural features and electronic properties of the dyes are accurately described within the TD-DFT framework.

The synthesis of three 9-diarylamino-substituted acridines is reported. The compounds of the donor–acceptor type – N,N-diphenylacridin-9-amine (1), 2,7-dimethyl-N,N-bis(4-methylphenyl)acridin-9-amine (2), and 2,7-bis(1-methyl-1-phenylethyl)-N,N-bis[4-(1-methyl-1-phenylethyl)phenyl]acridin-9-amine (3) were characterized by IR, 1H and 13C NMR, mass-spectral and elemental analysis. The crystal structures of compounds 1–3 and their protonated forms were determined by X-ray diffraction analysis. The absorption and fluorescence spectra were measured in various solvents. Solvatochromic shifts and dependence of the fluorescence quantum yields on the solvent polarity and protonation suggest the use of these compounds as chemical sensors. An example of a sensor material based on compound 2 is presented. Density functional theory calculations of the structures and time-dependent density functional theory calculations of the gas-phase excitation and emission energies of 1 were performed at the PBE0/SVP level of theory.