Monodisperse Starburst Oligofluorene‐Functionalized 4,4′,4″‐Tris(carbazol‐9‐yl)‐triphenylamines: Their Synthesis and Deep‐Blue Fluorescent Properties for Organic Light‐Emitting Diode Applications

Abstract

Four monodisperse starburst oligomers bearing a 4,4′,4″‐tris(carbazol‐9‐yl)‐triphenylamine (TCTA) core and six oligofluorene arms are synthesized and characterized. The lengths of oligofluorene arms vary from one to four fluorene units, giving the starburst oligomers molecular weights ranging from 3072 to 10 068 Da (1 Da = 1.66 × 10–27 kg). All of the starburst oligomers have good film‐forming capabilities, and display bright, deep‐blue fluorescence (λmax = 395–416 nm) both in solution and in the solid state, with the quantum efficiencies of the films (ΦPL) varying between 27 and 88 %. Electrochemical studies demonstrate that these materials have large energy gaps, and are stable for both p‐doping and n‐doping processes. Electroluminescent devices are successfully fabricated using these materials as hole‐transporting emitters, and emit deep‐blue light. Devices with luminance values up to 1025 cd m–2 at 11 V and luminous efficiencies of 0.47 cd A–1 at 100 cd m–2 have been produced, which translates to an external quantum efficiency of 1.4 %. In addition, these large‐energy‐gap starburst oligomers are good host materials for red electrophosphorescence. The luminance of the red electrophosphorescent devices is as high as 4452 cd m–2, with a luminous efficiency of 4.31 cd A–1 at 15 mA cm–2: This value is much higher than those obtained from the commonly used hole‐transporting materials, such as poly(vinyl carbazole) (PVK) (1.10 cd A–1 at 16 mA cm–2).

Fine‐Tuning of Yellow or Red Photo‐ and Electroluminescence of Functional Difluoro‐boradiazaindacene Films

“…[8] The doping of Alq 3 (q ¼ 8-hydroxyquinolate) with organic dyes has also been found to be a means of increasing the overall electroluminescence efficiency by allowing efficient energy transfer from the metal-containing matrix to the organic light-emitting dye. [9,10] Of major importance in the field of effective organic fluorophores are the difluoro-boradiazaindacenes, commonly named boron-dipyrromethene dyes (Bodipy). [11] These dyes are widely employed as useful fluorescence probes for labeling biomolecules [12] and for the sensing of calcium ions, [13] nitric oxides, [14] protons, [15] or various cations [16,17] by optoelectronic switching.…”

Photophysics of Fluorene Copolymers: Control of Fluorescence and Charge Separation by the Presence of Carbazole, Oxadiazole, or Biphenyl Units

“…9,10 To improve their optoelectronic properties, there is a continuous interest to synthesize suitably modified polyfluorenes for nanotechnology. 11,12 Herein, electron-donating unit, carbazole, and strong electronwithdrawing units, octafluorobiphenyl and oxadiazole, have been included into the polyfluorene chain to introduce electron donor and/or acceptor sites that could lead to an enhanced charge separation quantum yield and to long lifetimes of this transient state.…”

Fluorene-Based Conjugated Oligomers for Organic Photonics and Electronics

“…One paper puts one of each type of charge transport moiety on the oligofluorene [101]. Some also introduce these charge-transporting moieties as a central core with arms attached in direct conjugation [91,102] or as a central unit in the oligomer [103]. Direct conjugation with these moieties does influence their electronic and optical properties, which can be avoided by employing spiro-linked transport moieties [104], 9-position attachment of these arylamines [105], or alkyl spacers between the moieties [106,107].…”

“…In addition, through end-capping [93][94][95][96][97][98][99][100], substitution at the C-9 position [105], direct connection to such a core [91,102], or non-conjugated attachment through a flexible spacer [106,176], functionalization with electron-rich moieties contributes additional oxidation peaks in the CV scans. Similar non-conjugated attachment of electron-deficient moieties results in additional peaks in the reduction scans [106,176].…”

“…Incorporating electron-deficient moieties allows for a simpler device structure with an EQE of 1.6% [104], which can be an advantage or a disadvantage over non-functionalized oligofluorenes [103,104], depending on the details of the device structure [190]. To attain higher efficiencies with simpler, solution-processed devices, holetransport moieties are often incorporated into these oligomers with EQEs ranging from 1.4 to 3.7% [91,102,107,173,191,192]. Note that EQE is much more fair for the comparison of efficiency, as cd A -1 varies sharply with CIE color coordinate in the blue region of the spectrum [193].…”