New derivatives of triphenylamine and naphthalimide as ambipolar organic semiconductors: Experimental and theoretical approach

• Four derivatives of triphenylamine containing different number of naphthalimide moieties.
• Fluorescence quantum yields of the dilute solutions range from 0.63 to 0.78.
• Solvatochromic behaviour in polar solvents.
• Ambipolar charge transport in air with the mobilities of charges exceeding 10−4 cm2 V−1 s−1.
• Special role of methoxy groups in charge transport by means of hydrogen bonds.

Four new derivatives of triphenylamine containing different number of naphthalimide moieties were designed and synthesized by Suzuki condensation and their properties were studied by the experimental and theoretical tools. The compounds obtained are capable to form molecular glasses with glass transition temperatures ranging from 45 °C to 84 °C. They exhibit very high thermal stabilities with 5% weight loss temperatures ranging from 429 °C to 483 °C. Fluorescence quantum yields of the dilute solutions in nonpolar solvents of the synthesized materials range from 0.63 to 0.78. Due to the pronounced electron donor–acceptor character, the compounds show dramatic solvatochromic red shifts of fluorescence (up to 250 nm) in polar solvents. The ionization potentials of the solid samples of the compounds established by electron photoemission spectrometry in air ranged from 5.57 to 6.01 eV. 4-(4′-(Di-(4″-methoxyphenyl)amino)phenyl)-N-(2-ethylhexyl)-1,8-naphthalimide (5) was found to show ambipolar charge transport in air with the mobilities of charges exceeding 10−4 cm2 V−1 s−1 at high electric fields. The electron mobility of the compounds containing no methoxy groups were found to exceed the hole mobility by 2–3 orders of magnitude. The special role of methoxy groups in the ambipolar charge transport character of compound 5 is discussed in the frame of hopping Marcus theory, by applying a static theoretical analysis followed by a qualitative discussion of the positional disorder in some of these materials.

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