Fine-tuning of radiolysis induced emission by variable substitution of donor-/acceptor-substituted tetrakis(arylethynyl)benzenes

Emission from charge recombination between radical cations and anions of various tetrakis(arylethynyl)benzenes (TAEBs) was measured during pulse radiolysis in benzene (Bz). The formation of TAEB in the excited singlet state ((1)TAEB*) can be attributed to the charge recombination between TAEB (*+) and TAEB (*-), which is initially generated from the radiolytic reaction. It was found that the charge recombination between TAEB (*+) and TAEB (*-) gave (1)TAEB* as the emissive species but not excimers because of the large repulsion between substituents caused by the rotation around C-C single bonds. Since donor-/acceptor-substituted TAEBs possess three types of charge-transfer pathways (linear-conjugated, cross-conjugated, and "bent"-conjugated pathways between the donor and acceptor substituents through the ethynyl linkage), the emission spectra of (1)TAEBs* with intramolecular charge transfer (ICT) character depend on the substitution pattern and the various types of donor and acceptor groups during pulse radiolysis. Through control of the substitution pattern (e.g., the position of the nitrogen atom within the pyridine ring or the number of acceptors per arene ring of the regioisomeric donor-/acceptor-substituted TAEBs with donating N, N-dibutylamino and accepting pyridine unit (N1-9) and those with donating N, N-dibutylamino and accepting one (F1-3), two trifluoromethyl (F4-6), or perfluorinated arene (F7-9) units), fine-tuning of radiolysis induced emission color can be achieved.     

Gold-Catalyzed Regiospecific Annulation of Unsymmetrically Substituted 1,5-Diynes for the Precise Synthesis of Bispentalenes

Precise control of the selectivity in organic synthesis is important to access the desired molecules. We demonstrate a regiospecific annulation of unsymmetrically substituted 1,2-di(arylethynyl)benzene derivatives for a geometry-controlled synthesis of linear bispentalenes, which is one of the promising structures for material science. A gold-catalyzed annulation of unsymmetrically substituted 1,2-di(arylethynyl)benzene could produce two isomeric pentalenes, but both electronic and steric effects on the aromatics at the terminal position of the alkyne prove to be crucial for the selectivity; especially a regiospecific annulation was achieved with sterically blocked substituents; namely, 2,4,6-trimetyl benzene or 2,4-dimethyl benzene. This approach enables the geometrically controlled synthesis of linear bispentalenes from 1,2,4,5-tetraethynylbenzene or 2,3,6,7-tetraethynylnaphthalene. Moreover, the annulation of a series of tetraynes with a different substitution pattern regioselectively provided the bispentalene scaffolds. A computational study revealed that this is the result of a kinetic control induced by the bulky NHC ligands.     

Photophysical properties of 1,3,6,8-tetrakis(arylethynyl)pyrenes with donor or acceptor substituents: their fluorescence solvatochromism and lightfastness

We prepared a series of 1,3,6,8-tetrakis(arylethynyl)pyrenes with donor or acceptor substituents and investigated their photophysical properties. Solvent polarity hardly affected on the UV/vis spectra of all of the tetrakis(arylethynyl)pyrenes used in this study. On the other hand, electron-donating groups, NMe₂ and NPh₂ groups imparted fluorescence solvatochromicity to the skeleton by intramolecular charge transfer in the excited state. Furthermore, a tetrakis(arylethynyl)pyrene showed better lightfastness upon exposure to laboratory weathering using a xenon long arc lamp than coumarin.     

Facile Synthesis of Functionalized Bis(arylethynyl)benzene Derivatives via Sila–Sonogashira Reaction

This article describes a facile synthesis of a new series of symmetrical bis(arylethynyl)benzene derivatives via a one-pot coupling reaction between trialkylsilyl protected arylalkynyes and aryldihalides bearing both electron-withdrawing (EW) and electron-donating groups (ED) in the presence of PdCl₂(PPh₃)₂(5%) / CuI/tetrabutylammonium fluoride / triethylamine / tetrahydrofuran (sila–Sonogashira reaction) at room temperature.     

Photophysical investigation of neutral and diprotonated free-base bis(arylethynyl)porphyrins

The photophysical properties for a series of free-base arylethynyl porphyrins and the corresponding trans-disubstituted tetraphenylporphyrin (H(2)TPP) derivatives lacking arylethynyl functionalities have been studied via electronic absorption and emission spectroscopy in both neutral and diacid forms. Enhanced substituent effects on porphyrin absorption spectra are observed in the arylethynyl porphyrins relative to the H(2)TPP derivatives, owing to the presence of the ethynyl spacer that allows for a coplanar geometry between the porphyrin macrocycle and the appended phenyl substituents. Upon protonation, both series of porphyrins exhibit substantially red shifted absorption and emission spectra and enhanced oscillator strengths, with the magnitude of the spectral shifts being more substantial in the presence of the ethynyl functionalities. Spectral features of the arylethynyl porphyrin bearing p-dimethylamino substituents closely resemble those previously classified as "hyperporphyrin spectra" and are indicative of excited-state charge-transfer character. Protonation of both series of porphyrins results in reduced fluorescence lifetimes and enhanced nonradiative decay rates, and the impact of protonation on these parameters is attenuated in the presence of the arylethynyl functionalities. Our results coupled with previous structural data showing that arylethynyl porphyrins exhibit less structural distortion upon diacid formation relative to H(2)TPP further substantiate the proposal that significant alteration of porphyrin photophysical properties upon diacid formation can be attributed to nonplanar structural distortions induced by protonation.     

The effect of substrate structure on the direction of cyclization of ortho-alkynylbenzene diazonium salts

The cyclization of ortho-(arylethynyl)benzene diazonium salts (the Richter reaction) is studied. A reaction mechanism, which differs radically from that reported earlier is proposed and substantiated by experimental data and quantum-chemical calculations.     

Systematic structure-property investigations and ion-sensing studies of pyridine-derivatized donor/acceptor tetrakis(arylethynyl)benzenes

Nine structural isomers of a tetrakis(arylethynyl)benzene chromophore functionalized with dibutylaniline and pyridine units as respective donors and acceptors have been synthesized and their steady-state spectroscopic parameters investigated. The effects of small structural variations on the electronic absorption and emission spectra have been explored in evaluation of their potential as optical materials components. These structural variations have predictable consequences and thus allow fine-tuning of the optoelectronic properties for specialized applications. Strong solvatochromism is also displayed. Their response to protonation and metal ion complexation caused dynamic shifts in the emission spectra, providing evidence for a stepwise intramolecular charge-transfer switching phenomenon manifested by either hypsochromic or bathochromic shifts in the fluorescence lambda max. These shifts are believed to correlate strongly to the relative energies of the fluorophore's HOMO and LUMO levels. The complete array of compounds represents an interesting set of candidates for fluorescent sensing device components.     

4,5-Bis(arylethynyl)-1,2,3-triazoles—A New Class of Fluorescent Labels: Synthesis and Applications

Cu-catalyzed 1,3-dipolar cycloaddition of ethyl 2-azidoacetate to iodobuta-1,3-diynes and subsequent Sonogashira cross-coupling were used to synthesize a large series of new triazole-based push–pull chromophores: 4,5-bis(arylethynyl)-1H-1,2,3-triazoles. The study of their optical properties revealed that all molecules have fluorescence properties, the Stokes shift values of which exceed 150 nm. The fluorescent properties of triazoles are easily adjustable depending on the nature of the substituents attached to aryl rings of the arylethynyl moieties at the C4 and C5 atoms of the triazole core. The possibility of 4,5-bis(arylethynyl)-1,2,3-triazoles’ application for labeling was demonstrated using proteins and the HEK293 cell line. The results of an MTT test on two distinct cell lines, HEK293 and HeLa, revealed the low cytotoxicity of 4,5-bis(arylethynyl)triazoles, which makes them promising fluorescent tags for labeling and tracking biomolecules.     

New photoswitching unit for magnetic interaction: diarylethene with 2,5-bis(arylethynyl)-3-thienyl group

Photoswitching of the intramolecular magnetic interaction was demonstrated using diarylethenes with 2,5-bis(arylethynyl)-4-methyl-3-thienyl side group. Two nitroxide radicals were placed at each end of the 2,5-bis(arylethynyl)-4-methyl-3-thienyl group. Three kinds of aryl groups, 2,5-thienylene, p-phenylene, and m-phenylene groups, were used in the arylethynyl moiety. The diarylethene photoswitching units have an extended pi-conjugated chain on one side of the diarylethene. The photochromic reactivity was dependent on the arylethynyl group. Diarylethenes with m-phenylene group showed an efficient photochromic reactivity. Along with the photochromic reaction the diarylethenes showed photoswitching of an ESR spectrum originating from the change in the magnetic interaction between two unpaired electrons. The open-ring isomer showed stronger exchange interaction than the photogenerated closed-ring isomer. The magnetic interaction between two radicals via the pi-conjugated chain was altered by photocyclization due to the change of the hybrid orbital at the 2-position of the thiophene ring from sp(2) to sp(3).     

Emission from charge recombination during the pulse radiolysis of arylethynylpyrenes

Emission from several 1-(arylethynyl)pyrenes with a substituent on the aryl group (REPy, R = phenyl (PEPy), 4-dimethylaminophenyl (NPEPy), 4-isopropoxyphenyl (OPEPy), 2-quinonyl (QEPy), and 9-(10-cyanoanthracenyl) (AEPy)) was studied with time-resolved fluorescence measurements during pulse radiolysis in benzene. NPEPy and AEPy showed only monomer emission, while PEPy, OPEPy, and QEPy showed both monomer and excimer emissions during pulse radiolysis. In addition, REPy's also showed long-lived emissions with very weak intensities in the absence of oxygen, which were assigned to the "P-type" delayed fluorescence derived from the triplet-triplet annihilation. The formation of REPy's in the singlet excited state (1REPy*) can be interpreted as the charge recombination between the REPy radical cation and anion (REPy*+ and REPy*-, respectively), which are initially generated from the radiolytic reaction in benzene. Both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of PEPy are localized on the 1-pyrenyl (Py) moiety, while the HOMO of REPy's with an electron donating or withdrawing substituent on the benzene ring (R(D)EPy such as NPEPy and OPEPy or R(A)EPy such as QEPy and AEPy) is mainly localized on the donor moieties (R(D) or Py) and the LUMO on the acceptor ones (Py or R(A), respectively). Therefore, it is suggested that the one-electron oxidation and reduction of REPy's can occur from the donor and acceptor moieties, respectively. This scheme reasonably explains the relationship between the annihilation enthalpy changes (-Delta H' degrees) for the charge recombination of REPy*+ and REPy*- and the singlet excitation energies (E'(S1) of the REPy's. The results are compared with those in electrogenerated chemiluminescence.     

Intramolecular dehydro Diels-Alder reactions of diarylacetylenes: switching between benzo[b]- and benzo[c]fluorenones as products by controlling the rearrangement of cyclic allene intermediates

Thermal cyclization of 1-[2-(arylethynyl)phenyl]-3-trimethylsilylpropynones affords a mixture of benzo[b]fluorenones and benzo[c]fluorenones. The ratio of the two isomers can be efficiently varied between 100:0 and 0:100 by introducing substituents with appropriate electronic and steric properties on the aryl rings and using an appropriate solvent.     

Cruciforms' polarized emission confirms disjoint molecular orbitals and excited states

Steady-state and time-resolved polarized spectroscopy studies reveal that electronic excitation to the third excited state of 1,4-distyryl-2,5-bis(arylethynyl)benzene cruciforms results in fluorescence emission that is shifted an angle of ca. 60°. This result is consistent with quantum chemical calculations of the lowest electronic excited states and their transition dipole moments. The shift originates from the disjointed nature of the occupied molecular orbitals being localized on the different branches of the cruciforms.     

Local aromaticity study of heterocycles using n-center delocalization indices: the role of aromaticity on the relative stability of position isomers

A quantitative study on local aromaticity based on n-center electron delocalization indices, n being the number of atoms in the ring, is performed on a series of heterocycles containing N, O or S. The results indicate that the order of stability within a series of position isomers is not controlled by aromaticity but by other structural factors. Thus, for a certain series of monocycles position isomers (diazoles, triazoles, tetrazoles, diazines, triazines, and tetrazines) the most stable compound is the least aromatic one and vice versa. However, aromaticity controls the stability for series of isomers where these structural factors are similar. For the case of isocompounds, like isobenzopyrrole, isobenzofuran or isobenzothiophene, the large decrease in the aromaticity of the benzene ring with regard to their isomers makes them less stable.     

Gold-Catalyzed Facile Synthesis and Crystal Structures of Benzene-/Naphthalene-Based Bispentalenes as Organic Semiconductors

The gold-catalyzed facile synthesis of U-shaped and S-shaped bispentalenes is described from easily available tetra(arylethynyl)-benzenes and -naphthalenes. The optoelectronic and transistor properties were also investigated. The selectivity between the U-shaped and S-shaped bispentalene isomers can be tuned by the bulkiness of the ligand and the substrates. The S-shaped naphthalene-based bispentalene shows a one-dimensional face-to-face packing pattern in solid state and a good hole mobility, indicating that the S-shaped bispentalene core is highly suitable for transistor applications. The gold-catalyzed annulation of tetraynes provides a useful protocol in the synthesis of bispentalenes for organic semiconductors.     

Magnetic properties and aromaticity of o-, m-, and p-benzyne

The relative aromaticities of the three singlet benzyne isomers, 1,2-, 1,3-, and 1,4-didehydrobenzenes have been evaluated with a series of aromaticity indicators, including magnetic susceptibility anisotropies and exaltations, nucleus-independent chemical shifts (NICS), and aromatic stabilization energies (all evaluated at the DFT level), as well as valence-bond Pauling resonance energies. Most of the criteria point to the o-benzyne相似文献   

Control of the Solid‐State Chiral Optical Properties of a Supramolecular Organic Fluorophore Containing 4‐(2‐Arylethynyl)‐Benzoic Acid

The solid‐state chiral optical properties of a 4‐(2‐arylethynyl)‐benzoic acid/amine supramolecular organic fluorophore can be controlled by changing the arylethynyl group of the achiral 4‐(2‐arylethynyl)‐benzoic acid component molecule rather than the chirality of the amine component molecule.     

Recherches sur le benzofuranne. LVI. Synthèses dans la série de l'Euparone par acétylation de benzofurannes acétylés et méthoxylés sur l'homocycle

Unsubstituted benzofuran derivatives acetylatcd and methoxy-lated on the benzenoid moiety can be further acetvlated either on the benzene or on the furan ring - with or without demethylation depending upon the different cases. A series of new isomers of Euparone (2,5-diacetyl-6-hydroxybenzofuran) and its corresponding ether has thus been formed.     

新显色剂2-(2-噻唑偶氮)-5-二乙氨基苯甲酸分光光度法测定微量钴

近年来,杂环偶氮苯甲酸类显色剂取得了较快的发展。由于氨基取代结构对试剂性能有较大的影响^[1],因此本文合成了新显色剂2-(2-噻唑偶氮)-5-二乙氨基苯甲酸,(TAEB)并研究了它与钴的显色反应。     

对环芳烷二氯化产物组成的GC-MS表征

对环芳烷([2,2]Paracyclophane,简称PCP）是指苯环对位桥联的化合物,PCP及其氯代PCP的重要用途是通过升华、裂解、聚合等步骤沉积于物体表面形成聚合膜,该聚合膜具有透湿和透气小、抗化学腐蚀和抗辐射等优良性能[1,2].     

Synthesis of benzo[h]quinoline-based neutral pentacoordinate organosilicon complexes

Reactions of 10-benzo[h]quinolyllithium with a series of organosilanes led to the formation of neutral pentacoordinate complexes. The diethynyl-substituted complex was able to be converted to di(arylethynyl)-substituted ones by the Sonogashira-Hagihara coupling reaction. Electronegative substituents shortened N-Si distances and enhanced fluorescence intensity from the complexes.