Carlos

Hand in hand: Enantiopure reactants have been used to generate rigid molecular tweezers by Buchwald–Hartwig aminations. These result in the phenazine units curving in only one direction with formation of one product exclusively.

A series of novel AIE-active (aggregation-induced emission) molecules, named SAF-2-TriPE, SAF-3-TriPE, and SAF-4-TriPE, were designed and synthesized through facile reaction procedures. We found that incorporation of the spiro-acridine-fluorene (SAF) group, which is famous for its excellent hole-transporting ability and rigid structure, at different substitution positions on the phenyl ring affected the conjugation lengths of these compounds. Consequently, we have obtained molecules with different emission colors and properties without sacrificing good EL (electroluminescence) characteristics. Accordingly, a device that was based on compound SAF-2-TriPE displayed superior EL characteristics: it emitted green light with η_{c, max}=10.5 cd A⁻¹ and η_{ext, max}=4.22 %, whereas a device that was based on compound SAF-3-TriPE emitted blue-green light with η_{c, max}=3.9 cd A⁻¹ and η_{ext, max}= 1.71 %. These compounds also displayed different AIE performances: when the fraction of water in the THF solutions of these compounds was increased, we observed a significant improvement in the Φ_F of compounds SAF-2-TriPE and SAF-3-TriPE; in contrast, compound SAF-4-TriPE showed an abnormal phenomenon, in that it emitted a strong fluorescence in both pure THF solution and in the aggregated state without a significant change in Φ_F. Overall, this systematic study confirmed a relationship between the regioisomerism of the luminophore structure and its AIE activity and the resulting electroluminescent performance in non-doped devices.

Luminophores for organic LEDs: A series of new molecules, named SAF-2-TriPE, SAF-3-TriPE, and SAF-4-TriPE, that contain a quasi-TPE (tetraphenylethene) subunit were developed (see figure). These compounds displayed typical AIE (aggregation-induced emission) properties, with the exception of the more weakly emitting SAF-4-TriPE. Additionally, non-doped devices based on luminogens SAF-2-TriPE, SAF-3-TriPE, and SAF-4-TriPE were fabricated, and they displayed different electroluminescence properties with quantum efficiencies of 4.22, 1.71, and 1.42 %, respectively.

A new class of stabilized pentacene derivatives with externally fused five-membered rings are prepared by means of a key palladium-catalyzed cyclopentannulation step. The target compounds are synthesized by chemical manipulation of a partially saturated 6,13-dibromopentacene precursor that can be fully aromatized in a final step through a DDQ-mediated dehydrogenation reaction (DDQ=2,3-dichloro-5,6-dicyano-1,4-benzoquinone). The new 1,2,8,9-tetraaryldicyclopenta[fg,qr]pentacene derivatives have narrow energy gaps of circa 1.2 eV and behave as strong electron acceptors with lowest unoccupied molecular orbital energies between −3.81 and −3.90 eV. Photodegradation studies reveal the new compounds are more photostable than 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene).

Five in a row: A palladium-catalyzed cyclopentannulation followed by a DDQ-mediated dehydrogenation converts a partially hydrogenated pentacene precursor into stabilized pentacenes. These pentacene derivatives are excellent electron acceptors and have small energy gaps. DDQ=2,3-dichloro-5,6-dicyano-1,4-benzoquinone.

Triarylboron compounds have attracted much attention, and found wide use as functional materials because of their electron-accepting properties arising from the vacant p orbitals on the boron atoms. In this study, we design and synthesize new donor–acceptor triarylboron emitters that show thermally activated delayed fluorescence. These emitters display sky-blue to green emission and high photoluminescence quantum yields of 87–100 % in host matrices. Organic light-emitting diodes using these emitting molecules as dopants exhibit high external quantum efficiencies of 14.0–22.8 %, which originate from efficient up-conversion from triplet to singlet states and subsequent efficient radiative decay from singlet to ground states.

Triarylboron-based emitters are reported that show high photoluminescence quantum yields and efficient up-conversion from triplet to singlet states. Organic light-emitting diodes (OLEDs) using these emitters show a maximum external quantum efficiency of 21.6 % for a sky-blue OLED and 22.8 % for a green OLED.

3D photonic nanostructures with desirable functionalities in the visible light region and beyond have been recently given vast and increasing attentions because of the ability to control or confine electromagnetic waves in all three dimensions. Although substantial progress has been made in fabricating 3D nanostructures by means of lithography and nanotechnology, various bottlenecks still need to be overcome, and developing soft 3D stimuli-directed nanostructures with tailored properties remains a challenging but exciting work. In this context, soft nanotechnology—i.e., exploiting self-organized soft materials in nanotechnology—is emerging as a vibrant and burgeoning field of research in the bottom-up nanofabrication of intelligent stimuli-driven 3D photonic materials and devices. Liquid-crystalline materials undoubtedly represent such a marvelous dynamic system that combines the liquid-like fluidity and crystal-like ordering from molecular to macroscopic material levels. Importantly, being “soft” makes the materials responsive to various stimuli such as temperature, light, mechanical force, and electric and magnetic fields as well as chemical and electrochemical reactions, resulting in a fascinating tunability of dynamic photonic bandgaps in the 3D nanostructure that provides numerous opportunities in all-optical integrated circuits and next-generation communication systems. Here, the development of 3D photonic nanostructures is reviewed, culminating with perspectives for the future scope and challenges of these emerging soft 3D photonic nanostructures towards device applications.

Soft nanotechnology—i.e., exploiting self-organized soft materials in nanotechnology—is emerging as an attractive paradigm in the bottom-up nanofabrication of intelligent stimuli-driven 3D photonic materials and devices. Liquid-crystalline materials undoubtedly represent such an elegant dynamic system that combines the liquid-like fluidity and crystal-like ordering from molecular to macroscopic levels. This review provides a glimpse of the advancements in design, fabrication and applications of stimuli-directing self-organized 3D liquid-crystalline photonic nanostructures.

The crystal-packing structures of seven derivatives of diaroylmethanatoboron difluoride (1 a–gBF₂) are characterized by no overlap of the π-conjugated main units of two adjacent molecules (type I), overlap of the benzene ring π-orbitals of two adjacent molecules (type II), and overlap of the benzene and dihydrodioxaborinine rings π-orbitals of adjacent molecules (type III). The crystal-packing structures govern the fluorescence (FL) properties in the crystalline states. The FL domain that is present in type I crystals, in which intermolecular orbital interactions are absent, leads to excited monomer-like FL properties. In the case of the type II crystals, the presence of intermolecular overlap of the benzene rings π-orbitals generates new FL domains, referred to as “excited multimers”, which possess allowed S₀–S₁ electronic transitions and, as a result, similar FL lifetimes at longer wavelengths than the FL of the type I crystals. Finally, intermolecular overlap of the benzene and dihydrodioxaborinine ring π-orbitals in the type III crystals leads to “excited multimer” domains with forbidden S₀–S₁ electronic transitions and longer FL lifetimes at similar wavelengths as that in type I crystals.

Great excitations: A relationship between the fluorescence properties and crystal-packing structures of diaroylmethanatoboron difluorides was demonstrated. Photoexcitation of continuously stacked molecules with fused π-orbitals in the crystals lead to formation of neither excited monomers nor excimers, but a novel fluorescence domain “excited multimer”. The excited multimer exhibits variable fluorescence properties according to the manner of molecular overlap (see scheme).

First synthesis of the macrocycle cyclohexa(1,3-pyrenylene) is achieved in six steps starting with pyrene, leading to a non-aggregating highly twisted blue-light-emitting material. The cyclodehydrogenation of the macrocycle offers a promising synthesis route to holey-nanographene.

A double cone: A synthetic route is developed to give a double-cone shaped six-membered pyrene macrocycle, thus extending the aromatic system of the cyclohexa-m-phenylene.

One efficient way to prolong the emission wavelength of rhodamine analogs is to perturb the skeleton of the xanthene core with other atoms. Herein, phosphorus has been fused into a classic rhodamine framework to replace the bridge oxygen atom, yielding a phosphorus-substituted rhodamine. It exhibits extraordinary long-wavelength fluorescence emission, elongating to the region above 700 nm, with bathochromic shifts of 140 nm and 40 nm relative to rhodamine and Si-rhodamine, respectively. For more details see the Communication by T. Wang et al. on page 16754 ff.