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The donor-acceptor-π-conjugated (D-π-) 2 A fluorescent dyes OUY - 2 , OUK-2 and OUJ-2 with two (diphenylamino)carbazole thiophene units as D (electron-donating group)-π (π-conjugated bridge) moiety and a pyridine, pyrazine or triazine ring as electron-withdrawing group (electron-accepting group, A) have been designed and synthesized. The photophysical and electrochemical properties of the three dyes were investigated by photoabsorption and fluorescence spectroscopy, Lippert-Mataga plots, cyclic voltammetry and density functional theory calculations. The photoabsorption maximum (λ max,abs ) and the fluorescence maximum (λ max,fl ) for the intramolecular charge-transfer characteristic band of the (D-π-) 2 A fluorescent dyes show bathochromic shifts in the order of OUY-2 &lt; OUK-2 &lt; OUJ-2 . Moreover, the photoabsorption bands of the (D-π-) 2 A fluorescent dyes are nearly independent of solvent polarity, while the fluorescence bands showed bathochromic shifts with increasing solvent polarity (i.e., positive fluorescence solvatochromism). The Lippert-Mataga plots for OUY - 2 , OUK-2 and OUJ-2 indicate that the Δμ (= μ e - μ g ) value, which is the difference in the dipole moment of the dye between the excited (μ e ) and the ground (μ g ) states, increases in the order of OUY-2 &lt; OUK-2 &lt; OUJ-2 . Therefore, the fact explains our findings that OUJ-2 shows large bathochromic shifts of the fluorescence maxima in polar solvents, as well as the Stokes shift values of OUJ-2 in polar solvents are much larger than those in nonpolar solvents. The cyclic voltammetry of OUY - 2 , OUK-2 and OUJ-2 demonstrated that there is little difference in the HOMO energy level among the three dyes, but the LUMO energy levels decrease in the order of OUY-2 &gt; OUK - 2 &gt; OUJ - 2 . Consequently, this work reveals that for the (D-π-) 2 A fluorescent dyes OUY - 2 , OUK-2 and OUJ-2 the bathochromic shifts of λ max,abs and λ max,fl and the lowering of the LUMO energy level are dependent on the electron-withdrawing ability of the azine ring, which increases in the order of OUY-2 &lt; OUK-2 &lt; OUJ-2 .

Synthesis, photophysical and electrochemical properties of pyridine, pyrazine and triazine-based (D–π–)2A fluorescent dyes

Synthesis, photophysical and electrochemical properties of pyridine, pyrazine and triazine-based (D–π–)₂A fluorescent dyes