Molecular switches flipped by oxygen

One-Pot Synthesis of 1,3-Cyclohexadienes by Birch Reduction in the Presence of Carbonyl Compounds

Birch reductions are well-known transformations of arenes, applied for large scale synthesis of 1,4-cyclohexadienes. Herein, we describe first reactions of benzoic acids in the presence of carbonyl compounds, affording aldol products in moderate to high yields. Alkyl aldehydes give the expected nonconjugated dienes by reaction at the α-position. Interestingly, the intermediately formed enolate attacks aryl aldehydes and ketones from its γ-position, which can be explained by steric hindrance. This opens the door for the one-pot synthesis of 1,3-cyclohexadienes, which are not accessible by classical Birch reductions. Our method is applicable to benzoic, m- and p-toluic acid and various carbonyl compounds, and more than 25 new products were isolated in up to 93 % yield. Prochiral aryl aldehydes afford diastereomeric mixtures in ratios of about 4 : 1, but in the cyclohexadiene ring only trans isomers are formed with high selectivity. Finally, the 1,3-cyclohexadienes are suitable precursors for further transformations, which we have demonstrated in first examples. Thus, aromatization affords products of a formal meta selective Friedel-Crafts alkylation, and four new stereocenters were generated by cycloaddition of singlet oxygen with excellent selectivity.

Spatiotemporal Release of Singlet Oxygen in Low Molecular Weight Organo-Gels Upon Thermal or Photochemical External Stimuli

The first example of a material capable of spatiotemporal catch and release of singlet oxygen (1O2) in gel phase is presented. Several low molecular weight organogelators based around an oxotriphenylhexanoate (OTHO) core are developed and optimized with regard to; their gelation properties, and ability of releasing 1O2 upon thermal and/or photochemical external stimuli, in both gel phase and solution. Remarkably, reversible phase transitioning between the gel and solution phase are also demonstrated. Taken together two complementary modes of releasing 1O2, one thermally controlled over time, and one rapid release by means of photochemical stimuli is disclosed. These findings represent the first phase reversible system where function and aggregation properties can be controlled independently, and thus pave the way for novel applications in material sciences as well as in life sciences.

Tandem Oxidative Dearomatizations of Diphenylanthracene Atropisomers

The first examples of tandem oxidative dearomatizations of 9,10-diphenylanthracene atropisomers with ortho,ortho'- formyl substituents are presented. In the presence of KMnO4, their stereoselective tandem double oxidation and spirocyclization mainly afford the syn or anti dearomatized 9,10-diphthalide anthracenes. Using Pinnick's reagent and depending on the conditions, the oxidation can mainly lead to the corresponding syn or anti diacids in good yields or to three oxidation products. An unprecedented further oxidative ring expansion toward dibenzo[b,e]oxepines is also reported.

Hetero-Diels-Alder Reaction between Singlet Oxygen and Anthracene Drives Integrative Cage Self-Sorting

A ZnII8L6 pseudocube containing anthracene-centered ligands, a ZnII4L'4 tetrahedron with a similar side length as the cube, and a trigonal prism ZnII6L3L'2 were formed in equilibrium from a common set of subcomponents. Hetero-Diels-Alder reaction with photogenerated singlet oxygen transformed the anthracene-containing "L" ligands into endoperoxide "LO" ones and ultimately drove the integrative self-sorting to form the trigonal prismatic cage ZnII6LO3L'2 exclusively. This ZnII6LO3L'2 structure lost dioxygen in a retro-Diels-Alder reaction after heating, which resulted in reversion to the initial ZnII8L6 + ZnII4L'4 ⇌ 2 × ZnII6L3L'2 equilibrating system. Whereas the ZnII8L6 pseudocube had a cavity too small for guest encapsulation, the ZnII6L3L'2 and ZnII6LO3L'2 trigonal prisms possessed peanut-shaped internal cavities with two isolated compartments divided by bulky anthracene panels. Guest binding was also observed to drive the equilibrating system toward exclusive formation of the ZnII6L3L'2 structure, even in the absence of reaction with singlet oxygen.

Singlet Oxygen Responsive Molecular Receptor to Modulate Atropisomerism and Cation Binding

In switchable molecular recognition, ¹ O₂ stimulus responsive receptors offer a unique structural change that is rarely exploited. The employed [4+2] reaction between ¹ O₂ and anthracene derivatives is quantitative, reversible and easily implemented. To evaluate the full potential of this new stimulus, a non-macrocyclic anthracene-based host was designed for the modular binding of cations. The structural investigation showed that ¹ O₂ controlled the atropisomerism in an on/off fashion within the pair of hosts. The binding studies revealed higher association constants for the endoperoxide receptor compared to the parent anthracene, due to a more favoured preorganization of the recognition site. The fatigue of the ¹ O₂ switchable hosts and their complexes was monitored over five cycles of cycloaddition/cycloreversion.

Chiral Anthranyl Trifluoromethyl Alcohols: Structures, Oxidative Dearomatization and Chiroptical Properties

Chiral trifluoromethyl alcohol groups were introduced at the hindered ortho positions of 9,10-diphenylanthracenes to investigate their effects on the physical properties and reactivity towards oxidative dearomatization. In such compact structures, the position in different quadrants and the preferred orientation of the -CH(OH)CF₃ groups were determined by the relative and absolute configurations of each stereoisomer, respectively. As a consequence, the stereochemistry governs the organization of the H-bonded molecules in single crystals (homochiral dimers vs ribbon), whereas in chlorinated solvents, they all behave as discrete compounds. Concerning their reactivity, the stereospecific dearomative oxidation of these molecules leads to 9,10-bis-spiro-isobenzofuran-anthracenes, when using organic single-electron transfer oxidants. The chiroptical properties of the alcohols and the corresponding dearomatized products were compared and showed an important modulation of the intensity.

Chemically Driven Rotatory Molecular Machines

Molecular machines are at the frontier of biology and chemistry. The ability to control molecular motion and emulating the movement of biological systems are major steps towards the development of responsive and adaptive materials. Amazing progress has been seen for the design of molecular machines including light-induced unidirectional rotation of overcrowded alkenes. However, the feasibility of inducing unidirectional rotation about a single bond as a result of chemical conversion has been a challenging task. In this Review, an overview of approaches towards the design, synthesis, and dynamic properties of different classes of atropisomers which can undergo controlled switching or rotation under the influence of a chemical stimulus is presented. They are categorized as molecular switches, rotors, motors, and autonomous motors according to their type of response. Furthermore, we provide a future perspective and challenges focusing on building sophisticated molecular machines.

Aromatic Endoperoxides

The fundamental aspects of aromatic endoperoxide chemistry are reviewed including their synthesis and reactions. The discussion will focus on factors that will both enhance and prevent the formation of aromatic endoperoxides, and on structural features that will provide control over their ability to release singlet oxygen. This approach recognizes the dual use of aromatic hydrocarbons as both precursors of endoperoxides and as valuable materials for incorporation in electronic and photonic devices. Improvement of the existing methods and development of new methods for the synthesis of endoperoxides is necessary as result of the demand to improve existing and to create new applications for these valuable materials. On the other hand, prevention of endoperoxide formation is crucial to inhibit irreversible oxidative degradation of aromatic hydrocarbons and to extend their lifetimes as useful organic semiconductors.

Chemically Triggered Release of Singlet Oxygen from Bisphenalenyl Endoperoxides with a Brønsted Acid

Aromatic endoperoxides have emerged as intriguing stimulus-responsive materials for molecular oxygen (O₂) storage and delivery but are currently limited in their application because they require heat to trigger O₂ release. Here we present the first example of acid-triggered singlet oxygen (¹O₂) release that does not require external heating by treating bisphenalenyl endoperoxides (EPOs) with trifluoroacetic acid. Mechanistic studies reveal that diprotonation of EPOs leads to a >10-fold increase in cycloreversion rates by lowering the energy of activation (ΔE_a) by as much as 71.1 kJ mol^-1. Remarkably, acid-catalyzed ¹O₂ release is even demonstrated at room temperature. Chemical trapping experiments indicate that reactive ¹O₂ is present during acid-triggered release, which is promising for the development of these molecular materials for metal-free, on-demand ¹O₂ delivery.

Controlled, Sunlight-Driven Reversible Cycloaddition of Multiple Singlet Oxygen Molecules to Anthracene-Containing Trianglimine Macrocycles

Controlled release of singlet oxygen is of interest not only to chemists, but also to biologists and medics involved in cancer therapy. Two chiral polyaza macrocyclic compounds and their corresponding endoperoxides have been synthesized. These peroxides exhibit high temperature stability, up to 80 °C. Detailed studies on their structure, including X-ray analysis as well as NMR, UV-VIS ECD spectroscopy and theoretical calculations, combined with photochemical measurements indicate that their high stability is related to the arrangement of oxygen atoms in a conformationally stable macrocyclic ring. Despite the change of carbon hybridization from sp2 to sp3 at the 9 and 10 positions of the anthracene units, the macrocyclic skeleton of the obtained compounds does not change its conformation. The obtained endoperoxides can be formed and release singlet oxygen by irradiation with UV light of 365 and 275 nm, respectively. Release of the oxygen does not degrade the macrocyclic structure.

Self-Sensitized and Reversible O2 Reactivity with Bisphenalenyls for Simple, Tunable, and Multicycle Colorimetric Oxygen-Sensing Films

Monitoring the levels of molecular oxygen (O₂) is critical for numerous applications, but there is still a long-standing challenge to develop robust and cost-effective colorimetric sensors that enable detection by changes in color. Current technologies employ chromophores that require additional additives, which inherently increase the cost and complexity. Here, we report that bisphenalenyls (PQPLs) function as the single active component for colorimetric O₂ sensing through their quantitative conversion into aromatic endoperoxides (EPOs). PQPLs display self-sensitizing reactivity: they are capable of generating singlet oxygen and binding it without the need for external photosensitizers. The rates of PQPL photooxygenation depend on the electron-donating ability of substituents, which highlights a simple strategy for tuning O₂ sensitivity. EPOs are stable under ambient conditions but can be thermally stimulated to convert back to PQPLs and concomitantly release O₂. Polymer-supported (PTMSP) films of PQPLs (2 wt %) reproduce these reactivity trends with a rapid red-to-colorless transition that is visible to the naked eye within 1 h of exposure and show a very low limit of detection (<5 ppm O₂). Films are chemically and thermally robust and maintain up to >99% of their original colorimetric response when reused and subjected to multiple cycles of photooxygenation and O₂ release. The simplicity and solution processability of these materials highlight their potential as "intelligent" inks for printable colorimetric sensors.

Linear Extension of Anthracene via B←N Lewis Pair Formation: Effects on Optoelectronic Properties and Singlet O2 Sensitization

The functionalization of polycyclic aromatic hydrocarbons (PAHs) via B←N Lewis pair formation offers an opportunity to judiciously fine-tune the structural features and optoelectronic properties, to suit the demands of applications in organic electronic devices, bioimaging, and as sensitizers for singlet oxygen generation. We demonstrate that the N-directed electrophilic borylation of 2,6-di(pyrid-2-yl)anthracene offers access to linearly extended acene derivatives Py-BR (R=Et, Ph, C₆ F₅ ). In comparison to indeno-fused 9,10-diphenylanthracene, the formal "BN for CC" replacement in Py-BR selectively lowers the LUMO, resulting in a much reduced HOMO-LUMO gap. An even more extended conjugated system with seven six-membered rings in a row (Qu-BEt) is obtained by borylation of 2,6-di(quinolin-8-yl)anthracene. Fluorinated Py-BPf shows particularly advantageous properties, including relatively lower-lying HOMO and LUMO levels, strong yellow-green fluorescence, and effective singlet oxygen sensitization, while resisting self-sensitized conversion to its endoperoxide.

Substituent Effect in Pyridinium Alkynylanthracenes on their Performance as Photosensitizers for Photodynamic Therapy

Progress in photodynamic therapy (PDT) relies on the design and synthesis of photosensitizers that can efficiently sensitize singlet oxygen using visible light irradiation while displaying limited dark toxicity. Here, we highlight the paper by Linker and coworkers published in this issue of Photochemistry and Photobiology, which evaluates the effect of the regiochemistry of pyridinium rings in three isomeric pyridinium alkynylanthracenes on their performance as photosensitizers for PDT in HeLa cells.

An Air-Stable Organic Radical from a Controllable Photoinduced Domino Reaction of a Hexa-aryl Substituted Anthracene

Air-stable organic radicals and radical ions have attracted great attention for their far-reaching application ranging from bioimaging to organic electronics. However, because of the highly reactive nature of organic radicals, the design and synthesis of air-stable organic radicals still remains a challenge. Herein, an air-stable organic radical from a controllable photoinduced domino reaction of a hexa-aryl substituted anthracene is described. The domino reaction involves a photoinduced [4 + 2] cycloaddition reaction, rearrangement, photolysis, and an elimination reaction; ¹H/¹³C NMR spectroscopy, high resolution mass spectrometry, single-crystal X-ray diffraction, and EPR spectroscopy were exploited for characterization. Furthermore, a photoinduced domino reaction mechanism is proposed according to the experimental and theoretical studies. In addition, the effects of employing push and pull electronic groups on the controllable photoinduced domino reaction were investigated. This article not only offers a new blue emitter and novel air-stable organic radical compound for potential application in organic semiconductor applications, but also provides a perspective for understanding the fundamentals of the reaction mechanism on going from anthracene to semiquinone in such anthracene systems.

Phase-Dependent Reactivity and Host-Guest Behaviors of a Metallo-Macrocycle in Liquid and Solid-State Photosensitized Oxygenation Reactions

The photochemical oxygenation reactions of a host-guest complex, pCp⊂[Ag₂L0](SbF₆)₂ (pCp = [2.2]paracyclophane) have been investigated in solution and in the solid state, using the macrocyclic ligand L0 having four anthracene moieties in the framework. As a result, it was found that the reactivity and host-guest functions show remarkable phase dependence. In solution, the photosensitized oxygenation of all the anthracene moieties of L0 resulted in a fully oxygenated macrocycle [Ag₂L4](SbF₆)₂ as the final product, while simultaneously the guest molecule was dissociated from the macrocyclic cavity. On the other hand, in an amorphous solid of pCp⊂[Ag₂L0](SbF₆)₂ prepared by decomposing single crystals through the removal of the crystalline solvent, the oxygenated site of L0 was significantly controlled to provide a site-selectively oxygenated inclusion complex, pCp⊂[Ag₂L1](SbF₆)₂, possessing a mono-oxygenated C_s-symmetrical macrocyclic skeleton.

Stereoselective [4+2] Cycloaddition of Singlet Oxygen to Naphthalenes Controlled by Carbohydrates

Stereoselective reactions of singlet oxygen are of current interest. Since enantioselective photooxygenations have not been realized efficiently, auxiliary control is an attractive alternative. However, the obtained peroxides are often too labile for isolation or further transformations into enantiomerically pure products. Herein, we describe the oxidation of naphthalenes by singlet oxygen, where the face selectivity is controlled by carbohydrates for the first time. The synthesis of the precursors is easily achieved starting from naphthoquinone and a protected glucose derivative in only two steps. Photooxygenations proceed smoothly at low temperature, and we detected the corresponding endoperoxides as sole products by NMR. They are labile and can thermally react back to the parent naphthalenes and singlet oxygen. However, we could isolate and characterize two enantiomerically pure peroxides, which are sufficiently stable at room temperature. An interesting influence of substituents on the stereoselectivities of the photooxygenations has been found, ranging from 51:49 to up to 91:9 dr (diastereomeric ratio). We explain this by a hindered rotation of the carbohydrate substituents, substantiated by a combination of NOESY measurements and theoretical calculations. Finally, we could transfer the chiral information from a pure endoperoxide to an epoxide, which was isolated after cleavage of the sugar chiral auxiliary in enantiomerically pure form.

Effect of Twisting on the Capture and Release of Singlet Oxygen by Tethered Twisted Acenes

The use of polyaromatic hydrocarbons to capture and release singlet oxygen is of considerable importance in materials chemistry, synthesis, and photodynamic therapy. Here we studied the ability of a series of tethered twistacenes, possessing different degrees of backbone twist, to capture and release singlet oxygen via the reversible Diels–Alder reaction. When the twistacene acts as both a sensitizer and a diene, the photo-oxidation rate depends on the extinction coefficient of the irradiation wavelength. However, when the twistacenes function solely as a diene, the rate of photo-oxidation increases with increasing twist. The rate of the reverse reaction, the singlet oxygen release, also increases with increasing twist. The calculated transition state energy decreases with increasing twist, which can explain the observed trend. The presence of the tether significantly increases the reversibility of the reaction, which can proceed in repeated forward and reverse cycles in very high yield under mild conditions, as required for molecular switches.

Molecular Springs: Integration of Complex Dynamic Architectures into Functional Devices

Molecular/supramolecular springs are artificial nanoscale objects possessing well-defined structures and tunable physicochemical properties. Like a macroscopic spring, supramolecular springs are capable of switching their nanoscale conformation as a response to external stimuli by undergoing mechanical spring-like motions. This dynamic action offers intriguing opportunities for engineering molecular nanomachines by translating the stimuli-responsive nanoscopic motions into macroscopic work. These nanoscopic objects are reversible dynamic multifunctional architectures which can express a variety of novel properties and behave as adaptive nanoscopic systems. In this Minireview, we focus on the design and structure-property relationships of supramolecular springs and their (self-)assembly as a prerequisite towards the generation of novel dynamic materials featuring controlled movements to be readily integrated into macroscopic devices for applications in sensing, robotics, and the internet of things.

Acenes beyond organic electronics: sensing of singlet oxygen and stimuli-responsive materials

Although they are often detrimental in organic electronics, the cycloaddition reactions of acenes, especially with singlet oxygen, are useful in a range of responsive materials.

Self-assembled coordination thioether silver(I) macrocyclic complexes for homogeneous catalysis

The bis-ortho-thioether 9,10-bis[(o-methylthio)phenyl]anthracene was synthesized as a syn-atropisomer, as revealed by X-ray diffraction. This alkylaryl thioether ligand (L) formed different macrocyclic complexes by coordination with silver(I) salts depending on the nature of the anion: M₂L₂ for AgOTf and AgOTFA, M₆L₄ for AgNO₃. A discrete M₂L complex was obtained in the presence of bulky PPh₃AgOTf. These silver(I) complexes adopted similar structures in solution and in the solid state. As each sulfur atom in the ligand is prochiral, macrocycles L₂M₂ were obtained as mixtures of diastereoisomers, depending on the configurations of the sulfur atoms coordinated to silver cations. The X-ray structures of the two L₂·(AgOTf)₂ stereoisomers highlighted their different geometry. The catalytic activity of all silver(I) complexes was effective under homogeneous conditions in two tandem addition/cycloisomerization of alkynes using 0.5–1 mol % of catalytic loading.

Alkylation-, Heating-, and Doping-Induced Emission Enhancement of a Polyaromatic Tube in the Solid State

A polyaromatic tube with a subnanometer-sized cavity was efficiently prepared on a gram-scale through the stereo-controlled cyclotrimerization of a diphenylanthracene derivative as a key step. The facile exterior alkylation of the polyaromatic framework leads to a moderately fluorescent tube (R=-OC₁₀ H₂₁ ; Φ_F =20 %) in the solid state. The emission intensity of the solid-state alkyl-substituted tube is remarkably enhanced upon heating (up to 1.6 times, Φ_F =31 %) as well as doping with fluorescent dyes (up to 4.2 times, Φ_F =83 %) through efficient energy transfer.

Photooxygenation and gas-phase reactivity of multiply threaded pseudorotaxanes

The solution-phase photooxygenation of multiply threaded crown/ammonium pseudorotaxanes containing anthracene spacers is monitored by electrospray ionization Fourier-transform ion-cyclotron-resonance (ESI-FTICR) mass spectrometry. The oxygenated pseudorotaxanes are mass-selected and fragmented by infrared multiphoton dissociation (IRMPD) and/or collision-induced dissociation (CID) experiments and and their behavior compared to that of the non-oxygenated precursors. [4+2]Cycloreversion reactions lead to the loss of O2, when no other reaction channel with competitive energy demand is available. Thus, the release of molecular oxygen can serve as a reference reaction for the energy demand of other fragmentation reactions such as the dissociation of the crown/ammonium binding motifs. The photooxygenation induces curvature into the initially planar anthracene and thus significantly changes the geometry of the divalent, anthracene-spacered wheel. This is reflected in ion-mobility data. Coulomb repulsion in multiply charged pseudorotaxanes assists the oxygen loss as the re-planarization of the anthracene increases the distance between the two charges.

Base catalysed decomposition of anthracene endoperoxide

Anthracene endoperoxide (EPO) decomposes even under very mild basic conditions to anthraquinone (AQ) and hydrogen peroxide by an interesting mechanism, proposed herein.

Amphiphilic tribranched scaffolds with polyaromatic panels that wrap perylene stacks displaying unusual emissions

A spherical assembly containing a perylene stack, prepared from a rigid tribranched scaffold and perylene, exhibits unusual Y-emission in water at room temperature. In contrast, an analogous assembly from a flexible scaffold and perylene shows E-emission under the same conditions.

Intramolecular Transfer of Singlet Oxygen

The intramolecular transfer of energy (FRET) and electrons (Dexter) are of great interest for the scientific community and are well-understood. In contrast, the intramolecular transfer of singlet oxygen ((1)O2), a reactive and short-lived oxygen species, has until now been unknown. This process would be very interesting because (1)O2 plays an important role in photodynamic therapy (PDT). Herein, we present the first successful intramolecular transfer of (1)O2 from a donor to acceptor. Also, we found a dependence of conformation and temperature comparable with those of FRET. We provide several pieces of evidence for the intramolecular character of this transfer, including competition experiments. Our studies should be interesting not only from the theoretical and mechanistic point of view but also for the design of new (1)O2 donors and applications in PDT.

Reactivity of a pyridinium-substituted dimethyldihydropyrene switch under aerobic conditions: self-sensitized photo-oxygenation and thermal release of singlet oxygen

A reversible photo-switch is converted into an endoperoxide when irradiated with red light under air. This photo-produced species thermally releases ¹O₂.

Reversible oxygen addition on a triplet sensitizer molecule: protection from excited state depopulation

The molecular “chaff-flares” strategy for the protection of the triplet excited state from quenching by oxygen.

Internal and external stereoisomers of squaraine rotaxane endoperoxide: synthesis, chemical differences, and structural revision

Photooxygenation of permanently interlocked squaraine rotaxanes with anthracene-containing macrocycles produces the corresponding squaraine rotaxane endoperoxides (SREPs) quantitatively. SREPs are stored at low temperature, and upon warming, they undergo clean cycloreversion, releasing singlet oxygen and emitting light. The structural elucidation in 2010 assigned the structure as the SREP-int stereoisomer, with the endoperoxide unit directed inside the macrocycle cavity. New experimental and computational evidence reported here proves that the initial, kinetic photooxygenation product is the less stable SREP-ext stereoisomer with the endoperoxide unit directed outside the macrocycle. The photophysical properties and subsequent reactivity of mechanically strained SREP-ext depend on the size of the end groups of the encapsulated squaraine dye. If the end groups are sufficiently large to prevent dissociation of the interlocked components, the strained SREP-ext stereoisomer undergoes clean thermal cycloreversion. However, smaller squaraine end groups allow transient dissociation, resulting in a pseudorotaxane dissociation/association process that produces SREP-int as the thermodynamic stereoisomer that does not cyclorevert. The large difference in endoperoxide reactivity for the two SREP stereoisomers illustrates the power of the mechanical bond to induce cross-component steric strain and selective enhancement of a specific reaction pathway. The new insight enabled synthetic development of triptycene-containing squaraine rotaxanes with high fluorescence quantum yields and large Stokes shifts.

Intermediates in the Formation and Thermolysis of Peroxides from Oxidations with Singlet Oxygen

Herein we describe the recent mechanistic understandings of the singlet oxygen ene reaction to give hydroperoxides and the [4+2] cycloaddition affording endoperoxides. Both experimental findings and theoretical work conclude in the formation of intermediates structurally similar to perepoxides during the ene reaction. Such intermediates mainly control the regio- and stereoselectivities of this reaction class. For the [4+2] cycloaddition, both a synchronous concerted reaction (benzene, naphthalenes) and a stepwise reaction with a non-symmetric zwitterionic intermediate (larger acenes) have been found. The thermolysis of endoperoxides derived from acenes proceeds stepwise for anthracenes, but in a concerted manner for less stable adducts such as naphthalene.

Nonvolatile liquid anthracenes for facile full-colour luminescence tuning at single blue-light excitation

Nonvolatile room-temperature luminescent molecular liquids are a new generation of organic soft materials. They possess high stability, versatile optical properties, solvent-free fluid behaviour and can effectively accommodate dopant dye molecules. Here we introduce an approach to optimize anthracene-based liquid materials, focussing on enhanced stability, fluorescence quantum yield, colour tunability and processability, with a view to flexible electronic applications. Enveloping the anthracene core in low-viscosity branched aliphatic chains results in stable, nonvolatile, emissive liquid materials. Up to 96% efficient energy-transfer-assisted tunable emission is achieved by doping a minute amount of acceptor dye in the solvent-free state. Furthermore, we use a thermoresponsive dopant to impart thermally controllable luminescence colours. The introduced strategy leading to diverse luminescence colours at a single blue-light excitation can be an innovative replacement for currently used luminescent materials, providing useful continuous emissive layers in developing foldable devices.

Double alkylene-strapped diphenylanthracene as a photostable and intense solid-state blue-emitting material

We report the synthesis and photochemical and photophysical properties of double alkylene-strapped 9,10-diphenylanthracene derivatives 3a-c (a: C6 strap, b: C7 strap, c: C8 strap) in which the reactive central aromatic ring of the anthracene moiety is protected by the double alkylene straps. Thus, 3a-c were much more resistant to photochemical reactions than the parent 9,10-diphenylanthracene (DPA). Furthermore, 3b in C6H12 as well as in a cast film and the powder state showed the highest fluorescence quantum yields among 3a, 3b, quadruple triethylsilyl-protected DPA 4, and DPA, wherein the C7 strap in 3b effectively serves to block fluorescence self-quenching.