Blue organic light emitting materials: Synthesis and characterization of novel 1,8-naphthalimide derivatives

• 1,8-Naphthalimide based derivatives have been synthesized and characterized.
• The derivatives show blue PL with narrow FWHM and high Stokes’ shifts.
• The derivatives have high melting points and high decomposition temperatures.
• The derivatives have low lying HOMO–LUMO energy levels.
• The derivatives possess good electron-transporting and hole-blocking properties.

A series of naphthalimide derivatives were designed and synthesized by substituting electron-donating phenoxy groups at the 4th position of 1,8-naphthalimide. Photophysical, thermal, electrochemical properties of the synthesized derivatives were studied. The photophysical studies revealed that by varying the substituents at the 4th position of the 1,8-naphthalimide backbone, the photoluminescence spectra can be readily tuned in the range 410–423 nm (solution) and 457–468 nm (thin film). The derivatives have high Stokes’ shifts and the Commission Internationale de l’Eclairage (CIE) coordinates are positioned in the deep blue region of the chromaticity diagram. Thermal analysis showed that the melting points are in the range 135–270 °C with good thermal stability of 260–275 °C. Electrochemical studies show the derivatives to have low-lying energy levels revealing that they possess good electron-transporting and hole-blocking properties. The ionization potentials and electron affinity are in the region of 6.30–6.36 eV and 3.31–3.43 eV, respectively, with energy band-gaps in the range 2.93–3.0 eV. The studies reveal that these energy values are relatively higher than the commonly used electron transporting materials. Hence these derivatives are potential candidates not only as electron transporting but also as hole blocking blue emitters for organic light-emitting diode applications.