Amorphous Fluorescent Organic Emitters for Efficient Solution-Processed Pure Red Electroluminescence:  Synthesis, Purification, Morphology, Solid-State Photoluminescence, and Device Characterizations

Abstract

New soluble and intrinsic amorphous red emitters 1 and 2 were obtained by Suzuki coupling. Due to the close molecular polarities, separation of target products from monocoupling impurities presents a challenge. The results showed highly pure 2 would be a potentially valuable fluorophore for solution-processed pure red electroluminescence in terms of visual sensitivity with respect to 1.

A Dithienylbenzothiadiazole Pure Red Molecular Emitter with Electron Transport and Exciton Self‐Confinement for Nondoped Organic Red‐Light‐Emitting Diodes

“…In the case of a red emitter based on 4,7-di(thiophen-2-yl)-2,1,3-benzothiadiazole end-capped with a 2-(carbazoyl-9-yl)-9,9-dioctylfluorenyl moiety, [6] a two-layer EL device exhibited an almost twofold increase in h ext in the presence of a HBL. This result indicates that hole transport dominates in the emitter, as expected from the presence of the carbazoyl block in the structure, and in agreement with previous observations.…”

“…1). [6] In this contribution, we report the fabrication of multilayered organic-LED structures based on compound 1 using vacuum deposition techniques. Analysis of the electrical and optical characteristics of devices with different architectures shows that, in addition to its attractive red-emitting properties, compound 1 exhibits hole-injection and electron-transporting properties that allow for the fabrication of efficient electroluminescent devices without a hole-blocking layer (HBL), unlike many known red-light-emitting materials based on donor-acceptor structures, in which hole transport is generally predominant in the solid state.…”

“…[2,3] The synthesis of 1 has been described previously. [6] In a dilute methylene chloride solution, the UV-vis absorption spectrum of 1 presents two absorption bands with maxima at 298 and 486 nm. The fluorescence-emission spectrum shows a maximum at 613 nm, with a photoluminescence quantum yield (F em ) of 0.58 using rhodamine B in ethanol as a reference.…”

“…82 8C in the first heating run, with no crystallization or melting up to 300 8C. [6] The highest occupied molecular orbital (HOMO, À5.4 eV) and lowest unoccupied molecular orbital (LUMO, À3.2 eV) energy levels were derived respectively from the onset of the oxidation and reduction waves determined by cyclic voltammetry in CH 2 Cl 2 / CH 3 CN (5:1 v/v) in the presence of n-Bu 4 NPF 6 as electrolyte, using Ag/AgCl as the reference electrode and ferrocene as an internal standard. The potential of compound 1 as a bulk red emitter in electroluminescent devices has been analyzed for three different multilayered architectures fabricated by sequential vacuum thermal deposition of MoO 3 and organic layers onto indium tin oxide (ITO)-coated glass electrodes.…”

Photophysical Properties of Two New Donor-Acceptor Conjugated Copolymers and Their Model Compounds: Applications in Polymer Light Emitting Diodes (PLEDs) and Polymer Photovoltaic Cells (PPCs)

“…Among the polymers tested for suitability as an active layer, poly(3-hexyl-thiophene) (P3HT) and poly(carbazole) (PCz) have emerged as promising candidates for applications in optoelectronic devices because of their exceptional properties [79,80]. However, alternative copolymers of [2,1,3]-benzothiadiazole (BT) acceptor units with various donor units have attracted particular attention for using them in high performance PSCs [81][82][83]. To optimize the material properties, conjugated polymers with alternating electron-rich and hole-rich units along their backbone have been extensively developed because their absorption spectra and band gap can be readily tuned by controlling the intramolecular charge transfer (ICT) from donors to acceptors [84].…”