Synthesis and luminescent properties of blue sextuple-hydrogen-bond self-assembly molecular duplexes bearing 4-phenoxy-1,8-naphthalimide moieties

Abstract Two novel blue light-emitting sextuple hydrogen-bonding self-assembly molecular duplexes bearing 4-phenoxy-1,8-naphthalimide fluorophores, namely PhNIHB and 2TPhNIHB, have been synthesized and characterized. Compared with their small molecular counterparts PhNI and 2TPhNI, the objective compounds exhibit 13–22 nm blue-shifted fluorescent emission, and much higher photoluminescence quantum yields (0.34 vs 0.18 for PhNIHB; 0.42 vs 0.27 for 2TPhNIHB) in solid state; and their thermal and morphological stability have been improved as well. Employing 2TPhNIHB or 2TPhNI as emitter, non-doped solution-processed light-emitting diodes with structure of ITO/PEDOT: PSS (40 nm)/PVK (40 nm)/blue emitter (70–80 nm)/CsF (1.5 nm)/Al (120 nm) have been fabricated. The 2TPhNI-based device gives yellow emission [CIE (0.38, 0.49)] with poor maximum luminous efficiency (LEmax) of 0.13 cd/A and external quantum efficiency (EQEmax) of 0.06%. The 2TPhNIHB-based device, however, gives blue-green emission [CIE (0.25, 0.34)], with much higher efficiency relative to 2TPhNI-based one (LEmax of 0.37 cd/A and EQEmax of 0.35%). The effective isolation of the naphthalimide fluorescent cores as well as the suppressed formation of exciplex at the PVK/emitter interface by these oligoamide motifs are suggested to be responsible for the improved EL performance.