Search

Herein, corannulene‐based quintuple [6]helicenes (Q[6]H‐1 and Q[6]H‐2) and [7]helicene (Q[7]H) were synthesized via penta‐fold Heck and Mallory reaction. Notably, Q[7]H represents the highest reported helicene based on corannulene. X‐ray crystallography reveals that Q[6]H‐2 adopts a propeller‐shaped conformation with a well‐preserved corannulene core, while Q[6]H‐1 and Q[7]H exhibit quasi‐propeller‐shaped conformations. Upon heating, conformer Q[6]H‐1 undergoes conversion to the thermodynamically more stable conformer Q[6]H‐2, whereas conformer Q[7]H remains unchanged due to larger steric congestion. Racemization of the enantiomer of Q[6]H‐1 and conformational conversion were observed simultaneously at elevated temperature, with DFT studies indicating a racemization barrier of 32.06 kcal ⋅ mol−1. In contrast, the racemization barrier for Q[6]H‐2 was calculated to be 45.46 kcal ⋅ mol−1, indicating exceptional chiral stability. Surprisingly, the bowl inversions of Q[6]H‐1 and Q[6]H‐2 conformers are somewhat inhibited by the helical blades, whereas this was not observed for other possible conformers of Q[6]H. These results first demonstrated that subtle conformational variations can lead to significant changes in chiral stability and bowl inversions of multiple helicenes. Due to the well‐preserved corannulene core, propeller‐shaped conformation and electron complementarity, Q[6]H‐2 can recognize fullerenes in both solution and solid state, which is a rare instance of co‐crystallization assembly between multiple helicenes and fullerenes. [ABSTRACT FROM AUTHOR]

In this contribution, we explored the photocyclization of thioethers to highly substituted dibenzothiophenes (DBT) using solely UV‐light without any need for additives. This cost‐effective, robust and environmentally friendly approach yielded phosphorescent compounds, which were characterized by X‐ray crystallography and state‐of‐the‐art photophysical methods. The resulting DBTs feature ultralong photoluminescence lifetimes and quantum yields close to unity in frozen glassy matrices. The reaction mechanism was elucidated in detail through a combination of quantum chemical calculations and experimental results, providing evidence that triplet states are involved in the cyclization process. Additionally, the photoreaction can also be induced within materials. For this purpose, the precursors were integrated into polymer films or polymer resins suitable for 3D printing. Irradiation of these polymeric objects allows motifs with ultralong phosphorescence to be irreversibly inscribed through the proceeding photocyclization. The in situ photogeneration of DBTs from aromatic thioethers overcomes the observed incompatibilities regarding solubility in polymer resins for 3D printing. [ABSTRACT FROM AUTHOR]

The development of multimode photopatterning systems based on supramolecular coordination complexes (SCCs) is considerably attractive in supramolecular chemistry and materials science, because SCCs can serve as promising platforms for the incorporation of multiple functional building blocks. Herein, we report a light‐responsive liquid‐crystalline metallacycle that is constructed by coordination‐driven self‐assembly. By exploiting its fascinating liquid crystal features, bright emission properties, and facile photocyclization capability, a unique system with spatially‐controlled fluorescence‐resonance energy transfer (FRET) is built through the introduction of a photochromic spiropyran derivative, which led to the realization of the first example of a liquid‐crystalline metallacycle for orthogonal photopatterning in three‐modes, namely holography, fluorescence, and photochromism. [ABSTRACT FROM AUTHOR]

Enzymes facilitate chemical conversions through the collective activity of aggregated components, but the marriage of aggregation‐induced emission (AIE) with molecular containers to emulate enzymatic conversion remains challenging. Herein, we report a new approach to construct a PtII‐based octahedral cage with AIE characteristics for the photocyclization of alkynylaniline by restricting the rotation of the pendant phenyl rings peripheral to the PtII corner. With the presence of water, the C−H⋅⋅⋅π interactions involving the triphenylphosphine fragments resulted in aggregation of the molecular cages into spherical particles and significantly enhanced the PtII‐based luminescence. The kinetically inert Pt‐NP chelator, with highly differentiated redox potentials in the ground and excited states, and the efficient coordination activation of the platinum corner facilitated excellent catalysis of the photocyclization of alkynylaniline. The enzymatic kinetics and the advantages of binding and activating substrates in an aqueous medium provide a new avenue to develop mimics for efficient photosynthesis. [ABSTRACT FROM AUTHOR]

The synthesis of 2‐azetidinones (β‐lactams) from simple acrylamide starting materials by visible‐light‐mediated energy transfer catalysis is reported. The reaction features a C(sp3)−H functionalization via a variation of the Norrish–Yang photocyclization involving a carbon‐to‐carbon 1,5‐hydrogen atom transfer (supported by deuterium labelling and DFT calculations) and can be used for the construction of a diverse range of β‐lactam products. [ABSTRACT FROM AUTHOR]

Doping main‐group elements has become a unique strategy to fine‐tune optoelectronic properties of organic π‐conjugated molecules. Herein, we report the first example of diazaphosphinine based polycyclic hydrocarbons (DP‐PAHs) via facile synthetic protocols. Synthesis of diazaphosphinine heterocycles harnesses mild and efficient P−N chemistry. The heterocycles readily undergo photocyclizations by using only oxidants. The photocyclization protocol is applicable to the heterocycles with various P‐centers. We successfully extended the protocols in extended DP‐PAHs with 13‐fused aromatic rings. Further adjusting P‐chemistry allows to efficiently fine‐tune the singlet and triplet emission characteristics. More importantly, single‐molecule white‐light‐emitting character was achieved via the balanced singlet and triplet emission of DP‐PAH. Therefore, this work opens up new horizons in the area of organic π‐conjugated materials. [ABSTRACT FROM AUTHOR]

Herein, we expose how the antagonistic relationship between solid‐state luminescence and photocyclization of oligoaryl alkene chromophores is modulated by the conjugation length of their alkenyl backbones. Heptaaryl cycloheptatriene molecular rotors exhibit aggregation‐induced emission characteristics. We show that their emission is turned off upon breaking the conjugation of the cycloheptatriene by epoxide formation. While this modification is deleterious to photoluminescence, it enables formation of extended polycyclic frameworks by Mallory reactions. We exploit this dichotomy (i) to manipulate emission properties in a controlled manner and (ii) as a synthetic tool to link together pairs of phenyl rings in a specific sequence. This method to alter the tendency of oligoaryl alkenes to undergo photocyclization can inform the design of solid‐state emitters that avoid this quenching mechanism, while also allowing selective cyclization in syntheses of polycyclic aromatic hydrocarbons. [ABSTRACT FROM AUTHOR]

Although heptagons are widely found in graphenic materials, the precise synthesis of nanocarbons containing heptagons remains a challenge, especially for the nanocarbons containing multiple‐heptagons. Herein, we show that photo‐induced radical cyclization (PIRC) can be used to synthesize multi‐heptagon‐embedded nanocarbons. Notably, a nanographene containing six heptagons (1) was obtained via a six‐fold cascade PIRC reaction. The structure of 1 was clearly validated and showed a Monkey‐saddle‐shaped conformation. Experimental bond analysis and theoretical calculations indicated that the heptagons in 1 were non‐aromatic, whereas the peripheral rings were highly aromatic. Compared to planar nanographene with the same number of π electrons, 1 had a similar optical gap due to a compromise between the decreased conjugation in the wrapped structure and enhanced electronic delocalization at the rim. Electrochemical studies showed that 1 had low‐lying oxidation potentials, which was attributed to the nitrogen‐doping. [ABSTRACT FROM AUTHOR]

Photoinduced hydroarylation of alkenes is an appealing synthetic strategy for arene functionalization. Herein, we demonstrated that aryl radicals generated from electron‐deficient aryl chlorides/bromides could be trapped by an array of terminal/internal aryl alkenes in the presence of [Pt(O^N^C^N)] under visible‐light (410 nm) irradiation, affording anti‐Markovnikov hydroarylated compounds in up to 95 % yield. Besides, a protocol for [Pt(O^N^C^N)]‐catalyzed intramolecular photocyclization of acrylanilides to give structurally diverse 3,4‐dihydroquinolinones has been developed. [ABSTRACT FROM AUTHOR]

Since carbon–carbon (C−C) covalent bonds are rigid and robust, the bond length is, in general, nearly constant and depends only on the bond order and hybrid orbitals. We report herein direct visualization of the reversible expansion and contraction of a C(sp3)−C(sp3) single bond by light and heat. This flexibility of a C−C bond was demonstrated by X‐ray analysis and Raman spectroscopy of hexaphenylethane (HPE)‐type hydrocarbons with two spiro‐dibenzocycloheptatriene units, the intramolecular [2+2] photocyclization of which and thermal cleavage of the resulting cyclobutane ring both occur in a single‐crystalline phase. The force constant of the contracted C−C bond is 1.6 times greater than that of the expanded bond. Since formation of the cyclobutane ring and contraction of the C−C bond lower the HOMO level by approximately 1 eV, the oxidative properties of these HPEs with a flexible C−C bond can be deactivated/activated by light/heat. [ABSTRACT FROM AUTHOR]

Patterning multiple images within a single element without crosstalk can significantly increase the information capacity and security, but it is challenging to enable the response capability in each image. Now, the patterning of crosstalk‐free yet cooperative‐thermoresponse images (holographic and fluorescent images) is successfully achieved by designing a liquid crystal (LC)/AIEgen system with a unique synergy. The AIEgen's fluorescence intensity is controlled by the LC, while the LC's phase transition is in turn promoted by the AIEgen. The fluorescent image contrast is significantly boosted by efficient energy transfer (ΦET: 96 %) from the LC to the AIEgen. The AIEgen's photocyclization for fluorescent patterning occurs in a zero‐order kinetic manner and can be completed within several minutes when assisted by the LC. The photocyclization conversion is quantitatively dependent on the aggregation size: α∼exp(‐d), and able to reach as high as 98 %. [ABSTRACT FROM AUTHOR]

A series of supramolecular assemblies of types [Ag8(L)4](PF6)8 and [Ag4(L)2](PF6)4, obtained from the tetraphenylethylene (TPE) bridged tetrakis(1,2,4‐triazolium) salts H4‐L(PF6)4 and AgI ions, is described. The assembly type obtained dependends on the N‐wingtip substituents of H4‐L(PF6)4. Changes in the lengths of the N4‐wingtip substituents enables controlled formation of assemblies with either [Ag4(L)2](PF6)4 or [Ag8(L)4](PF6)8 stoichiometry. The molecular structures of selected [Ag8(L)4](PF6)8 and [Ag4(L)2](PF6)4 assemblies were determined by X‐ray diffraction analyses. While H4‐L(PF6)4 does not exhibit fluorescence in solution, their tetra‐NHC (NHC=N‐heterocyclic carbene) assemblies do upon NHC–metal coordination. Upon irradiation, all assemblies undergo a light‐induced, supramolecule‐to‐supramolecule structural transformation by an oxidative photocyclization involving phenyl groups of the TPE core, resulting in a significant change of the luminescence properties. [ABSTRACT FROM AUTHOR]

Starting from readily available 7‐substituted 1‐indanones, products with a tetracyclo[5.3.1.01,704,11]undec‐2‐ene skeleton were obtained upon irradiation at λ=350 nm (eight examples, 49–67 % yield). The assembly of the structurally complex carbon framework proceeds in a three‐photon process comprising an ortho photocycloaddition, a disrotatory [4π] photocyclization, and a di‐π‐methane rearrangement. The flat aromatic core of the starting material is converted into a functionalized polycyclic hydrocarbon with exit vectors in three dimensions. Ring opening reactions at the central cyclopropane ring were explored, which enable the preparation of tricyclo[5.3.1.04,11]undec‐2‐enes and of tricyclo[6.2.1.01,5]undecanes. [ABSTRACT FROM AUTHOR]

Herein the novel tetraphenylethylene (TPE) derivative 1 was designed with an integration of aggregation‐induced emission (AIE), multi‐state mechanochromism and self‐recovery photochromism. The molecule was susceptible to grinding, heating and vapor fuming and showed corresponding transition of its emission colors. The heated powder or single crystal of 1 exhibited reversible photochromism. After a short period of UV irradiation, it showed a bright red color, but recovered to its original white appearance within 1 min. The photochromism is due to the formation of photocyclization intermediates upon UV irradiation, while the eversible mechanochromism is attributed to the weak molecular interactions derived from head‐to‐tail stacking of the molecules. This reversible multi‐state, high‐contrasted and rapid responsive mechanochromic and photochromic property cooperatively provide double enhancement of a multimode guarantee in advanced anti‐counterfeiting. [ABSTRACT FROM AUTHOR]

In a single photochemical operation (λ≥350 nm) an easily accessible indanone derivative was converted into a structurally complex precursor of the protoilludane sesquiterpenes. The product (60 % yield) contains all 15 carbon atoms of the skeleton in the required connectivity and was transformed into the natural product atlanticone C (9 steps, 6 % overall yield). In addition, it was shown that other protoilludanes, such as Δ6‐protoilludene and paesslerin A, can be prepared in a concise fashion via the photochemical key intermediate. The photochemical reaction cascade comprises an ortho photocycloaddition, a thermal disrotatory ring opening and a regioselective disrotatory [4π] photocyclization. [ABSTRACT FROM AUTHOR]

The transfer of stereoinformation is at the heart of asymmetric reactions. By incorporating the natural monoterpene l‐menthone into the backbone of a diarylethene, we achieved efficient chirality transfer upon photocyclization, resulting in the preferred formation of one major closed isomer in a diastereomeric ratio (d.r.) of 85:15. More significantly, we were able to completely reverse the diastereomeric outcome of the ring closure simply by altering the chemical environment or the irradiation conditions. As a result, we could selectively accumulate the less favored minor closed isomer, with remarkable d.r. values of >99:1 and 74:26, respectively. Computations revealed that a stability inversion after photocyclization is the basis for the observed unprecedented control over diastereoselectivity. Which way to go? The monoterpene l‐menthone was incorporated into the backbone of a photochromic diarylethene. Chirality transfer upon photocyclization leads to preferred formation of one major stereoisomer. Complete reversal of the diastereomeric outcome was achieved by altering either the chemical environment or the irradiation wavelength, resulting in selective formation of the minor isomer. [ABSTRACT FROM AUTHOR]

Photo-mediated 6π cyclization is a valuable method for the formation of fused heterocyclic systems. Here we demonstrate that irradiation of cyclic 2-aryloxyketones with blue LED light in the presence of an IrIII complex leads to efficient and high yielding arylation across a panoply of substrates by energy transfer. 2-Arylthioketones and 2-arylaminoketones also cyclize effectively under these conditions. Quantum calculation demonstrates that the reaction proceeds via conrotatory ring closure in the triplet excited state. Subsequent suprafacial 1,4-hydrogen shift and epimerization leads to the observed cis-fused products. [ABSTRACT FROM AUTHOR]

Upon irradiation, cyclic imines containing o-amido groups are shown to produce reactive intermediates, amino azaxylylenes, which undergo intramolecular cycloadditions to tethered unsaturated pendants to yield complex N,O-heterocycles having an additional spiro-connected nitrogen heterocyclic moiety. Modular assembly of the photoprecursors allows expeditious increase of the complexity of the target poly-heterocyclic scaffolds with a minimal number of experimentally simple reaction steps. The photocyclization and subsequent postphotochemical transformations are accompanied by an increase of Lovering's fsp3 factor, thus producing unprecedented three-dimensional molecular architectures, and offering extended sampling of chemical space. [ABSTRACT FROM AUTHOR]

Herein we show that replacing the two meso carbon atoms of the polycyclic aromatic hydrocarbon (PAH) bisanthene by boron atoms transforms a near-infrared dye into an efficient blue luminophore. This observation impressively illustrates the impact of boron doping on the frontier orbitals of PAHs. To take full advantage of this tool for the targeted design of organic electronic materials, the underlying structure-property relationships need to be further elucidated. We therefore developed a modular synthesis sequence based on a Peterson olefination, a stilbene-type photocyclization, and an Si-B exchange reaction to substantially broaden the palette of accessible polycyclic aromatic organoboranes and to permit a direct comparison with their PAH congeners. [ABSTRACT FROM AUTHOR]

A single-strand arylene-vinylene precursor containing four phenylene and three naphthylene units linked together with six vinylene spacers undergoes helical folding via sextuple photocyclization to give a [16]helicene core in a single step. The phenylene and naphthylene units are arranged in the precursor such that unfavorable side reactions (anthracene or benzoperylene formation) are avoided, and this is the key to the success of the one-step synthesis of [16]helicene, which is the longest [ n]helicene that has been synthesized to date. [ABSTRACT FROM AUTHOR]

Endowing both solvent independency and excellent thermal bistability, the benzobis(thiadiazole)-bridged diarylethene system provides an efficient approach to realize extremely high photocyclization quantum yields ( Φo-c, up to 90.6 %) by both separating completely pure anti-parallel conformer and suppressing intramolecular charge transfer (ICT). [ABSTRACT FROM AUTHOR]