The synthesis and photoluminescence characteristics of novel blue light-emitting naphthalimide derivatives

Substitution at the 4-position of 1,8-naphthalimide with electron-donating phenoxy or tert-butyl modified phenoxy groups, novel naphthalimide derivatives were obtained which emitted blue fluorescence with emission peaks of 425–444 nm in chloroform solution under UV irradiation, with highest relative photoluminescence quantum efficiency of 0.82. When in solid film, only compounds that contained ortho-tert-butylphenoxy substituents displayed blue photoluminescence of 438–451 nm, with highest absolute fluorescence quantum yield of 0.29; whereas other compounds showed greenish blue fluorescence at 471–478 nm, with highest absolute fluorescence quantum yield of 0.42. Cyclic voltammetry studies revealed that the molecules have low-lying energy levels of the lowest unoccupied molecular orbital (LUMO) ranging from −3.29 eV to −3.24 eV, and energy levels of the highest occupied molecular orbital (HOMO) ranging from −6.26 eV to −6.16 eV, suggesting they may possess good electron-transporting or hole-blocking properties. The findings indicate that the molecules offer potential as dopants as well as non-doping light-emitting materials with good electron injection capabilities for fabrication of blue or greenish blue organic light-emitting diodes.