Novel liquid crystalline organic semiconducting oligomers incorporating N-heterocyclic carbazole moieties for fluorescent OLEDs

Guang Hu,Stuart P Kitney,Stephen M Kelly,William Harrison,Mary O’Neill

doi:10.1080/02678292.2017.1306633

Abstract

ABSTRACTA novel class of nematic liquid crystalline organic semiconducting oligomers incorporating N-heterocyclic carbazole moieties has been synthesised using simple and highly efficient reaction pathways. The electroluminescent colour of these novel oligomers can be varied in a controlled manner by molecular design. The values of the ionisation potential and the electron affinity of these electroluminescent oligomers can also be matched by structural design to the Highest Occupied Molecular Orbital (HOMO) energy level of the electron-blocking layer and the Lowest Unoccupied Molecular Orbital (LUMO) energy level of electron-transporting layer in the Organic light emitting diodes to create low charge-injection barriers for electrons and holes, respectively leading to electroluminescence with an efficacy up to 4.1 cd A−1.

Highlights

Organic light emitting diodes (OLEDs) with high information content, active matrix addressing and full colour are a type of novel flat-panel display, which does not require backlighting and other mostly light-absorbing - components, such as the diffusers, colour filters and polarisers, used in LCDs [1,2,3,4,5]
The materials for OLEDs can be usually classified as lowmolecular-mass materials (LMMMs) [16,17,18,19,20], polymers [21,22,23,24,25,26,27,28,29] and oligomers [30,31,32,33,34,35,36]
3.1 Synthetic Discussion of Reaction Scheme 1 The synthesis and application of carbazole-functional derivatives have been of great interest in materials chemistry, especially in organic electronics, due to their intrinsic photo-physical and redox properties, e.g. relatively intense luminescence and reversible oxidation processes, π-stacking capability and ease of further derivation [44,45,46,47,48,49,50,51]

Summary

Introduction

Organic light emitting diodes (OLEDs) with high information content, active matrix addressing and full colour are a type of novel flat-panel display, which does not require backlighting and other mostly light-absorbing - components, such as the diffusers, colour filters and polarisers, used in LCDs [1,2,3,4,5]. One of the advantages of using organic materials for electroluminescence is that they can be designed with the desired functions, such as high hole or electron mobility and efficient electroluminescence. The electron affinity (EA, LUMO energy level) and ionisation potentials (IP, HOMO energy level) of charge-transport materials can be tuned to better match the work functions of electrodes [10,11,12]. These requirements for the material properties can be achieved by the design and synthesis of a variety of organic molecules. The materials for OLEDs can be usually classified as lowmolecular-mass materials (LMMMs) [16,17,18,19,20], polymers [21,22,23,24,25,26,27,28,29] and oligomers [30,31,32,33,34,35,36]

Methods

Results

Conclusion