A sextuple hydrogen bonding molecular duplex bearing 1,8-naphthalimide moieties and polymer light-emitting diode based on it

Abstract

In this paper, the molecular structure of a 1,8-naphthalimide fluorophore modified sextuple H-bond self-assembly homodimer, comprising two linear oligoamide molecular strands bearing arrays on one edge with complementary hydrogen bond sequences of DDADAA and AADADD, is characterized via¹H NMR, ESI-MS, ¹³C NMR, and elementary analysis. The target duplex emits strong yellowish green light with emission peaks at 518 nm and 535 nm under UV photoexcitation in solution and solid film, respectively, and its photoluminescence quantum efficiency (solid state) has been enhanced greatly compared to its small molecular 1,8-naphthalimide counterpart (0.637 versus 0.324). Employing the duplex and the counterpart as emitting dopants, two yellowish green polymer light-emitting diodes (PLED) with the device configuration of ITO/PEDOT:PSS (50 nm)/PFO + dopant (5wt%) (80 nm)/CsF (3 nm)/Al (150 nm) have been fabricated. The results indicate that the PLED with the duplex as emitter has dramatically improved performance, for example, a much higher external electroluminescence quantum efficiency (QE_ext) of 1.87% (ph/el), and a much lower turn-on voltage of 6.4 V, compared to the one with the counterpart as emitter (QE_ext: 0.12%; turn-on voltage: 15 V), suggesting that the incorporation of H-bond self-assembly motif with the light-emitting fluorophore is an effective way for the design of electroluminescent materials.