Search

The recent development of π-conjugated nanohoops in organic electronics has opened new perspectives for this family of curved materials. Addressing the difference arising from curved vs. non-curved materials is an important concern in order to highlight the specific properties of curved materials. Herein, we discuss the significant differences arising between [4]-cyclo-N-pyridine-2,7-carbazole [4]C-Py-Cbz and its linear counterpart, N-pyridine-2,7-tetracarbazole [4]L-Py-Cbz. This study gathers optical, electrochemical, structural, morphological and charge transport properties and highlights the key role played by the curvature. We notably show how the electronic effects of the pending pyridines differently affect the molecular orbitals energies. We have also shown how structural rearrangements between ground and first excited states can be at the origin of the peculiar emission of nanohoops. Finally, the huge difference in terms of charge transport properties was discussed. Nanohoop [4]C-Py-Cbz displays a field-effect mobility in the saturated regime μFEsat of 3.4 × 10-6 cm² V-1 s-1, six times higher than that of its linear analogue [4]L-Py-Cbz (5.7 × 10-7 cm² V-1 s-1). However, the detailed study of the charge transport properties shows that the linear analogue forms a semi-conducting layer with a lower trap density, more favourable to the charge hopping processes. Theoretical calculations have provided clues on the origin of these differences, revealing that despite the intensity of electronic couplings is significantly in favor of [4]L-Py-Cbz, their highly anisotropic character renders them more sensitive to defects and disorder. This is consistent with the fact that [4]C-Py-Cbz displays experimentally better charge transport properties than [4]L-Py-Cbz. Such a type of structure-property relationship study provides fundamental findings of interest for the future design of high-performance nanohoops. [ABSTRACT FROM AUTHOR]

Nanohoops, cyclic association of π‐conjugated systems to form a hoop‐shaped molecule, have been widely developed in the last 15 years. Beyond the synthetic challenge, the strong interest towards these molecules arises from their radially oriented π‐orbitals, which provide singular properties to these fascinating structures. Thanks to their particular cylindrical arrangement, this new generation of curved molecules have been already used in many applications such as host–guest complexation, biosensing, bioimaging, solid‐state emission and catalysis. However, their potential in organic electronics has only started to be explored. From the first incorporation as an emitter in a fluorescent organic light emitting diode (OLED), to the recent first incorporation as a host in phosphorescent OLEDs or as charge transporter in organic field‐effect transistors and in organic photovoltaics, this field has shown important breakthroughs in recent years. These findings have revealed that curved materials can play a key role in the future and can even be more efficient than their linear counterparts. This can have important repercussions for the future of electronics. Time has now come to overview the different nanohoops used to date in electronic devices in order to stimulate the future molecular designs of functional materials based on these macrocycles. [ABSTRACT FROM AUTHOR]

The performances of simplified single‐layer phosphorescent organic light‐emitting diodes (SL‐PhOLEDs) have significantly increased and they now appear to be a promising alternative to multi‐layer PhOLEDs. The blue and white emissions, far more challenging than all the other colours, are still particularly desired. Herein, a high efficiency host material for blue emitting SL‐PhOLED using the blue emitter FIr6 is reported, which is particularly interesting as it displays an emission at shorter wavelengths than the well‐known FIrpic emitter, almost exclusively reported in the SL‐PhOLEDs literature. The host material investigated herein is constructed on the electron‐rich quinolinoacridine and displays when incorporated in FIr6‐based SL‐PhOLEDs, an external quantum efficiency (EQE)⟩10% and a low Von of 3.1 V. This is the first work passing an EQE of 10% with FIr6 as an emitter. This host also reaches a very high EQE of 19% when used with the green emitter Ir(ppy)2acac, this performance being among the highest recorded for green SL‐PhOLEDs. Finally, as white SL‐PhOLEDs involve blue emitting SL‐PhOLEDs, this host is also used with a combination of blue and yellow emitters. An extremely high EQE of 24% is reached with CIE coordinates of (0.40;0.48). These findings show the real potential of the quinolinoacridine fragment to reach high performance multi‐colour SL‐PhOLEDs. [ABSTRACT FROM AUTHOR]

Designing deep‐blue fluorophores with a low CIEy is an important request for organic light‐emitting diode (OLED) technology either for display applications or to develop new applications such as light source with antibacterial properties. The challenge of deep‐blue emitting OLEDs mainly relies on the difficulty to reach efficient emitters fulfilling all the characteristics desired to insure a high device performance with suitable CIE coordinates. Herein, we report on the synthesis, the physico‐chemical properties and the application as emissive layer in an OLED of two deep‐blue emitters constructed on the association of Spirofluorene‐N‐PhenylAcridine (SPA‐F) and SpiroBiFluorene (SBF) molecular fragment. Two emitters, 2,2‐SPAF‐SBF and 2,3‐SPAF‐SBF have been constructed following a similar design strategy. The emission wavelength is tuned by the substitution pattern of the SBF backbone (meta or para linkage). Through a structure/properties relationship study, the electrochemical, photophysical and thermal/morphological properties are discussed. When used as emitter in a multi‐layer OLED, 2,2‐SPA‐SBF displays a deep‐blue emission reaching an EQE of ≈1.7% and a Von of 4 V. The electroluminescent spectrum displays a λmax below 400 nm (i.e. 394 nm) and CIE coordinates of (0.182, 0.054). The CIEy coordinate of 0.054 is low and fits the NTSC and EBU standards. [ABSTRACT FROM AUTHOR]

In the last ten years, the development of π‐conjugated nanohoops has been considerable owing to their remarkable properties. However, to date, their incorporation in organic electronic devices remains very scarce. In this work, the first high‐performance organic electronic device (i.e., phosphorescent organic light‐emitting diode, PhOLED) incorporating a nanohoop ([4]‐cyclo‐N‐butyl‐2,7‐carbazole, [4]C‐Bu‐Cbz) is reported, revealing the potential of nanohoops in electronics. Thus, using the red phosphor Ir(MDQ)2(acac), the [4]C‐Bu‐Cbz‐based PhOLED displays a high external quantum efficiency (EQE) of 17.0%, a current efficiency (CE) of 20.6 cd A−1 and a power efficiency (PE) of 25.8 lm W−1 demonstrating that the charge injection, transport, and recombination are particularly efficient. This performance is significantly higher than that of its linear counterpart, N‐butyl‐2,7‐quartercarbazole ([4]L‐Bu‐Cbz), which presents an EQE of 11.1%, a CE of 13.0 cd A−1 and a PE of 15.7 lm W−1. The significant difference, in terms of device performance, between cyclic and acyclic compounds provides a new basis to construct high‐performance electronic devices. This study, which includes optical, electrochemical, morphological, and charge transport properties, shows that nanohoops can be efficiently used as organic semiconductors in electronics and opens the way to their practical uses in high‐performance optoelectronic devices, which is now the next stage of their evolution. [ABSTRACT FROM AUTHOR]

Keywords: charge transport; cyclocarbazoles; hoop size effect; nanohoops EN charge transport cyclocarbazoles hoop size effect nanohoops 1 1 1 07/25/23 20230720 NES 230720 B The impact of the hoop size b on the electronic and charge transport properties of [5]- and [4]-cyclo- I N i -butyl-2,7-carbazoles is reported. Charge transport, cyclocarbazoles, hoop size effect, nanohoops. [Extracted from the article]

A new host material for Single-Layer Phosphorescent Organic Light-Emitting Diodes (SL-PhOLED) is reported, namely SPA-2-FDMB, using the dimesitylborane (DMB) fragment as an acceptor unit. The molecular design is constructed on the general donor-spiro-acceptor architecture, which consists of connecting, via a spiro bridge, a donor and an acceptor units in order to avoid strong interaction between them. The DMB fragment is known for many electronic applications (notably Aggregation-Induced Emission) but has not been used yet for SL-PhOLED applications. This appears particularly interesting, as the development of this simplified technology has shown that only a few electron-accepting fragments such as diphenylphosphine oxide can provide high-performance devices. Herein, the yellow-emitting SL-PhOLED using SPA-2-FDMB as host presents an External Quantum Efficiency of 8.1% (Current Efficiency of 24.9 cd.A -1 ) with a low threshold voltage of 2.6 V. As SPA-2-FDMB presents a sharp HOMO/LUMO difference, the good matching of HOMO and LUMO energy levels with the Fermi level of the electrodes is responsible for these performances. The low LUMO level of -2.61 eV also appears particularly important. These performances are, to date, the highest reported for a yellow/orange-emitting SL-PhOLED and show the potential of DMB unit in the single-layer technology., (© 2024 The Author(s). Small published by Wiley‐VCH GmbH.)

In the field of π-conjugated nanohoops, the size of the macrocycle has a strong impact on its structural characteristics, which in turn affect its electronic properties. In this work, we report the first experimental investigations linking the size of a nanohoop to its charge transport properties, a key property in organic electronics. We describe the synthesis and study of the first example of a cyclocarbazole possessing five constituting building units, namely [5]-cyclo-N-butyl-2,7-carbazole, [5]C-Bu-Cbz. By comparison with a shorter analogue, [4]-cyclo-N-butyl-2,7-carbazole, [4]C-Bu-Cbz, we detail the photophysical, electrochemical, morphological and charge transport properties, highlighting the key role played by the hoop size. In particular, we show that the saturated field effect mobility of [5]C-Bu-Cbz is four times higher than that of its smaller analogue [4]C-Bu-Cbz (4.22×10 -5 vs 1.04×10 -5  cm 2  V -1  s -1 ). However, the study of the other organic field-effect transistor characteristics (threshold voltage V TH and subthreshold slope SS) suggest that a small nanohoop is beneficial for good organization of the molecules in thin films, whereas a large one increases the density of structural defects, and hence of traps for the charge carriers. The present findings are of interest for the further development of nanohoops in electronics., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)