Synthesis And Photo-Electro Properties Of Novel Star-Shaped Molecules Of Triphenylamine With Terminal Groups Of Naphthalimide

A novel family of star-shaped molecules of triphenylamine with terminal groups of naphthalimide for single-layer organic electroluminescent devices has been designed and synthesized, in which triphenylamine unit performs as a hole-transport moiety, 1,8-naphthalimide unit performs as an electron-transport and emitting moiety. Their structures have been confirmed by HRMS, FT-IR and ¹HNMR spectra.The thermal stability of such compounds has been determined on a differential scanning calorimeter (DSC), and the temperature of the glassy state changed into the supercooled liquid state (T_g) is as high as 253²74℃ and the decomposing temperature is higher than 300℃. Thermal analysis results indicate that these compounds have relative high T_g and good thermal stability, which is very essential for fabricating stable organic EL devices.The compounds display greenish-yellow fluorescence in CHCl₃ and DMF. λ_F^max is red-shifted when the polarity of solvents is increased. λ_F^max is located at 500-514 run in CHCl₃ and530-538 nm in DMF. The Stokes shift of the compounds in solvents is longer than 87 nm, and it is also red-shifted when the polarity of solvents is increased, In DMF, the Stokes shift is over 100 nm.There exists an effective singlet-singlet energy transfer due to the overlap between the absorption of naphthalimide moiety and the emission of carbazole moiety, which quenches the emission of triphenylamine moiety and lowers the fluorescence quantum yield.The electrochemistry properties have been determined on Cyclic Voltammetry. Their band gaps (E_g) and ionization potentials (P₁) have been calculated at 2.46².59 eV and 5.54⁵.83eV respectively. The relationship between electrochemistry property and different substituents at 4-position of 1,8-naphthalimide has been discussed. The results indicate that the novel compounds are good candidates not only as hole-transport materials but also as electro-transpor materials for single-layer OLEDs.