Progress in long wavelength emission in fluorene-based electroluminescent blue materials

Abstract

On account of the advantages of organic electroluminescent materials compared with their inorganic counterparts, the development of organic electroluminescent materials is one of the hot areas of the optoelectronic materials. Fluorene and its derivatives, which have an aromatic biphenyl structure with a wide energy gap in the backbones and high luminescent efficiency, have drawn much attention of material chemists and device physicists. However, one drawback of fluorene-based electroluminescent blue materials is that there is an occurrence of long wavelength emission after annealing the films in air or after operating organic light-emitting diodes for a long time. To clarify the origin of this long wavelength emission, the scientists at home and abroad have put forward all kinds of correlative explanations. Among the scientists, some thought it was caused by excimer-related species, while some others claimed that it was caused by the fluorenone of photooxdized fluorene. The corresponding solutions to this problem have also been proposed and the problem has been partially resolved in some degree. The present review summarizes and analyzes the progress made on the origin of long wavelength emission in fluorene-based electroluminescent blue materials at home and abroad in the past few years. Some issues to be addressed and hotspots to be further investigated are also presented and discussed.fluorene, electroluminescent, long wavelength emission, fluorenone, excimer, synthesis

Effective adjustment of the optoelectronic properties of organic conjugated materials by synthesizing p-n diblock molecules

“…Of the three basic red, green and blue colors, the efficiency, color purity, and lifetime of the first two have almost met the commercialization requirements for full color displays [90,91], whereas the blue light still lags far behind. This difficulty constitutes a bottle-neck that strongly challenges academic and industrial researchers [92,93]. Therefore, it is very important to summarize some rules through a great deal of investigations to further guide the synthesis of new blue light-emitting materials with improved optoelectronic characteristics.…”

“…However, the dominant position of LCDs in market is being gradually challenged by flexible information display technologies such as organic light-emitting diodes (OLEDs) because of their easy processability, low turn-on voltage, wide viewing angle, and facile color tunability over the full visible range. With major efforts from both industry and academia, significant advancements have been made over the past few decades in this new flexible *Corresponding author (email: iamhjjiang@njupt.edu.cn) information display technology [1][2][3][4][5]. The simplest OLED sandwiches the emissive layer between two electrodes.…”

Purified polar polyfluorene for light-emitting diodes and light-emitting electrochemical cells

“…Due to the large band gap of polyfluorene [3−5] (PF) homopolymer, it is a highly attractive class of conjugated materials for blue light-emitting devices. However, PF-based blue light-emitting materials suffer from poor color stability due to the appearance of long-wavelength green emission in the photoluminescent (PL) or electroluminescent (EL) spectrum [6] . This phenomenon is extensively discussed in scientific literatures as a result of the formation of excimer/aggregate or ketonic defects resulting from photo-and/or electro-oxidation of polyfluorene chains [7−9] .…”

Organic Ambipolar Conjugated Molecules for Electronics: Synthesis and Structure–Property Relationships

“…[1][2][3][4][5] The performance and lifetime of these devices, such as organic light-emitting diodes (OLEDs), photovoltaics, electrochromes, memory, and organic field-effect transistors (OFETs), are critically dependent on the materials development, device design, deposition processes, and modeling, among which materials play a crucial role. The unique properties of organic semiconductor are largely based on the versatility to synthesize multifunctional conjugated materials by judicious molecular design.…”