Linear, sp-hybridised, 1-dimensional (1D) all-carbon wires are conceptually the simplest π-conjugated organic molecules. Their fundamental experimental and theoretical properties and their materials ...chemistry applications are under-developed compared to many other π-conjugated systems. The emphasis of this review is on the emerging applications of functional oligoynes and polyynes in molecular electronics and optoelectronics. The molecules considered herein contain at least two contiguous acetylene units (that is, a conjugated diacetylene or butadiynyl fragment). Relevant examples of cumulenes will also be included. Oligoynes/polyynes/cumulenes represent unique carbon nanostructures, among the so-called "synthetic carbon allotropes". The molecules are structurally versatile because the extent of conjugation and the electronic and photophysical properties can be tailored by judicious selection of end-groups, the number of alkyne units, and the option to incorporate metal atoms into the backbone. Their applications will be considered as molecular wires in electrode|(single)-molecule|electrode architectures, and as active components for non-linear optics, electrochromism, redox-activity, organic light emitting devices, photoinduced electron transfer systems, liquid crystals, bioimaging and biosensing, with emphasis on the role played by the special longitudinal properties of the carbon-wire units. Four to six contiguous triple bonds is generally the length limit of oligoynes for practical applications, due to the synthetic challenges and inherent instability of longer homologues under ambient conditions. The review will also outline appealing future directions for next-generation linear, sp-hybridised, all-carbon molecular wires with new and enhanced properties.
This review presents the multi-faceted applications of oligoynes in molecular electronics and optoelectronics, as well as recent insights for the design and properties of sp-hybridised carbon wires.
The development of metal complexes for optoelectronic applications is a fertile area of research. In contrast to the rigorous development of mononuclear metal complexes, dinuclear species have been ...less well studied and their fundamental chemistry and applications are under-explored. However, dinuclear species present special properties and functions compared with mononuclear species as a consequence of tuning the bridging ligands, the cyclometalated ligands or the two metal centers. More recently, dinuclear species have enabled important breakthroughs in the fields of OLEDs, photocatalytic water splitting and CO
2
reduction, DSPEC, chemosensors, biosensors, PDT, smart materials and so on. Here we present an overview of recent developments of dinuclear metal complexes, their multifunctional properties and their various applications. The relationship between structure and property of dinuclear species and important factors which influence device performance are discussed. Finally, we illustrate some challenges and opportunities for future research into dinuclear metal complexes. This review aims to provide an up-to-date summary and outlook of functional dinuclear metal complexes and to stimulate more researchers to contribute to this exciting interdisciplinary field.
Dinuclear metal complexes have enabled breakthroughs in OLEDs, photocatalytic water splitting and CO
2
reduction, DSPEC, chemosensors, biosensors, PDT and smart materials.
Purely organic molecules, which emit light by dual emissive (DE) pathways, have received increased attention in the last decade. These materials are now being utilized in practical optoelectronic, ...sensing and biomedical applications. In order to further extend the application of the DE emitters, it is crucial to gain a fundamental understanding of the links between the molecular structure and the underlying photophysical processes. This review categorizes the types of DE according to the spin multiplicity and time range of the emission, with emphasis on recent experimental advances. The design rules towards novel DE molecular candidates, the most perspective types of DE and possible future applications are outlined. These exciting developments highlight the opportunities for new materials synthesis and pave the way for accelerated future innovation and developments in this area.
In this review, types and mechanisms of dual emission, as well as recent new insights for the design and applications of efficient novel dual emissive organic materials are presented.
Thermally activated delayed fluorescence (TADF) emitters, which produce light by harvesting both singlet and triplet excitons without noble metals, are emerging as next-generation organic ...electroluminescent materials. In the past few years, there have been rapid advances in molecular design criteria, our understanding of the photophysics underlying TADF and the applications of TADF materials as emitters in organic light-emitting diodes (OLEDs). This topic is set to remain at the forefront of research in optoelectronic organic materials for the foreseeable future. In this Review, we focus on state-of-the-art materials design and understanding of the photophysical processes, which are being leveraged to optimize the performance of OLED devices. Notably, we also appraise dendritic and polymeric TADF emitters — macromolecular materials that offer the potential advantages of low cost, solution processable and large-area OLED fabrication.Thermally activated delayed fluorescence (TADF) emitters are promising electroluminescent materials for next-generation organic light-emitting diodes (OLEDs). In this Review, the molecular design, photophysical characteristics and OLEDs composed of small-molecule, dendritic and polymeric TADF emitters are discussed.
Chemical modification of phenothiazine‐benzophenone derivatives tunes the emission behavior from triplet states by selecting the geometry of the intramolecular charge transfer (ICT) state. A ...fundamental principle of planar ICT (PICT) and twisted ICT (TICT) is demonstrated to obtain selectively either room temperature phosphorescence (RTP) or thermally activated delayed fluorescence (TADF), respectively. Time‐resolved spectroscopy and time‐dependent density functional theory (TD‐DFT) investigations on polymorphic single crystals demonstrate the roles of PICT and TICT states in the underlying photophysics. This has resulted in a RTP molecule OPM, where the triplet states contribute with 89 % of the luminescence, and an isomeric TADF molecule OMP, where the triplet states contribute with 95 % of the luminescence.
Rapid and efficient utilization of triplet states to generate room temperature phosphorescence (RTP) or highly efficient thermally activated delayed fluorescence (TADF) is achieved by structural modification to give a planar or twisted intramolecular charge transfer (PICT or TICT) geometry, respectively.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
We show that the emitter and host combination must be optimized to minimize the reverse intersystem crossing (rISC) barrier and maximize thermally activated delayed fluorescence (TADF). The blue TADF ...emitter, 2,7-bis(9,9-dimethyl-acridin-10-yl)-9,9-dimethylthioxanthene-S,S-dioxide (DDMA-TXO2), has strong TADF character due to efficient charge transfer (CT) state formation. By combining DDMA-TXO2 with a host of correct polarity (DPEPO) that relaxes the CT manifolds’ energy to become resonant with the lowest-energy local triplet state of DDMA-TXO2, the emitter and host combination produce a minimum rISC barrier (ΔE ST), which maximizes TADF efficiency. We show that the sensitivity of these splittings is highly dependent on emitter environment and must be carefully tuned to optimize device performance. Devices utilizing DDMA-TXO2 in the DPEPO host show blue electroluminescence (EL), with commission internationale de l’éclairage (CIE) chromaticity coordinates of CIE (0.16, 0.24), with a maximum external quantum efficiency of 22.4%. This high device performance is a direct consequence of optimizing the TADF efficiency by this “host tuning”.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Oligo(arylene ethynylene) (OAE) derivatives are the "workhorse" molecules of molecular electronics. Their ease of synthesis and flexibility of functionalisation mean that a diverse array of OAE ...molecular wires have been designed, synthesised and studied theoretically and experimentally in molecular junctions using both single-molecule and ensemble methods. This review summarises the breadth of molecular designs that have been investigated with emphasis on structure-property relationships with respect to the electronic conductance of OAEs. The factors considered include molecular length, connectivity, conjugation, (anti)aromaticity, heteroatom effects and quantum interference (QI). Growing interest in the thermoelectric properties of OAE derivatives, which are expected to be at the forefront of research into organic thermoelectric devices, is also explored.
This review explores the synthetic variation of structural features of oligo(arylene ethynylene) (OAE) molecular wires and how this affects the electronic and thermal properties of OAE molecules or molecular assemblies held between electrodes.
Although persistent room‐temperature phosphorescence (RTP) emission has been observed for a few pure crystalline organic molecules, there is no consistent mechanism and no universal design strategy ...for organic persistent RTP (pRTP) materials. A new mechanism for pRTP is presented, based on combining the advantages of different excited‐state configurations in coupled intermolecular units, which may be applicable to a wide range of organic molecules. By following this mechanism, we have developed a successful design strategy to obtain bright pRTP by utilizing a heavy halogen atom to further increase the intersystem crossing rate of the coupled units. RTP with a remarkably long lifetime of 0.28 s and a very high quantum efficiency of 5 % was thus obtained under ambient conditions. This strategy represents an important step in the understanding of organic pRTP emission.
Persistence pays off: Bright persistent room‐temperature phosphorescence from pure organic molecules was achieved by intermolecular electronic coupling of selected units in crystals. The combined advantages of their different excited‐state configurations (i.e., the nπ* state with a high intersystem crossing rate and the ππ* state with a low radiative rate) results in a hybrid intersystem‐crossing process that leads to efficient persistent room‐temperature phosphorescence.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
WOLEDs offer new design opportunities in practical solid‐state lighting and could play a significant role in reducing global energy consumption. Obtaining white light from organic LEDs is a ...considerable challenge. Alongside the development of new materials with improved color stability and balanced charge transport properties, major issues involve the fabrication of large‐area devices and the development of low‐cost manufacturing technology. This Review will describe the types of materials (small molecules and polymers) that have been used to fabricate WOLEDs. A range of device architectures are presented and appraised.
White organic light‐emitting devices (WOLEDs) offer new design opportunities in practical solid‐state lighting and could play a significant role in reducing global energy consumption. Obtaining white light from organic LEDs is a considerable challenge. Alongside the development of new materials with improved color stability and balanced charge transport properties, major issues involve the fabrication of large‐area devices and the development of low‐cost manufacturing technology.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Regio- and conformational isomerization are fundamental in chemistry, with profound effects upon physical properties, however their role in excited state properties is less developed. Here two ...regioisomers of bis(10H-phenothiazin-10-yl)dibenzob,dthiophene-S,S-dioxide, a donor-acceptor-donor (D-A-D) thermally-activated delayed fluorescence (TADF) emitter, are studied. 2,8-bis(10H-phenothiazin-10-yl)dibenzob,dthiophene-S,S-dioxide exhibits only one quasi-equatorial conformer on both donor sites, with charge-transfer (CT) emission close to the local triplet state leading to efficient TADF via spin-vibronic coupling. However, 3,7-bis(10H-phenothiazin-10-yl)dibenzob,dthiophene-S,S-dioxide displays both a quasi-equatorial CT state and a higher-energy quasi-axial CT state. No TADF is observed in the quasi-axial CT emission. These two CT states link directly to the two folded conformers of phenothiazine. The presence of the low-lying local triplet state of the axial conformer also means that this quasi-axial CT is an effective loss pathway both photophysically and in devices. Importantly, donors or acceptors with more than one conformer have negative repercussions for TADF in organic light-emitting diodes.
PDF
