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Complementary to the previous assignment of the first, second, and fourth binding sites of human serum albumin (HSA) for 2-anthracenecarboxylate (AC) and the subsequent mediation of AC photocyclodimerization, the site-specific inhibition of the enantiodifferentiation by xenon allowed us to assign the remaining third and fifth AC-binding sites to subdomains IB and IIIB, respectively. This study reveals a clearer picture of the binding and photochirogenic behavior of HSA and further expands the scope of bio-supramolecular photochirogenesis. [ABSTRACT FROM AUTHOR]

The photo-induced oxidative cyclization of the 1,1′- p -phenylene-bis(2,4,6-triphenylpyridinium) was reinvestigated. While mono-cyclization was claimed to be the photoproduct in a previous report, it was found that the diazonia derivative of hexabenzoperylene can be formed as the final photoproduct by four-fold cyclization. The photoreaction affords one of the two possible stereoisomers (twisted and anti forms), and the stereostructure of the product is assigned to the twisted form by 1 H NMR titration study with a chiral complexing reagent and by analysis of the absorption spectrum using TD-DFT calculations. The diazonia derivative of hexabenzoperylene exhibits yellow and red luminescence in the solution and solid states respectively and possesses well-separated four-reversible one-electron reduction potentials. [ABSTRACT FROM AUTHOR]

The synthesis of vabicaserin analogues bearing a quaternary center or spiro substitution at the 4-position has been studied via a [6π]-acrylanilide cyclization employing flow photochemistry in a mesoscale and microfluidic flow photoreactor. The method is also used to synthesize 4,4'-disubstituted tetrahydroquinolines and, furthermore, enables the first synthesis of (±)-trans-vabicaserin. [ABSTRACT FROM AUTHOR]

A novel hexahelicene bearing a cyano group at a selected position on a middle aromatic ring has been synthesized, in good yield, through a short synthetic strategy involving the preparation of 2-bromo-5-cyanobenzo[ c ]phenanthrene as a synthetic intermediate. The racemate was resolved by HPLC on a chiral stationary phase providing both (+)- and (−)- 3 enantiomers with high optical purity. The absolute configurations of (+)- and (−)- 3 were assigned as P and M , respectively, by circular dichroism spectroscopy. The optical properties of the hexacyclic helicene were investigated and showed interesting behaviour. [ABSTRACT FROM AUTHOR]

New acenaphthylene-based dithienylethenes have been prepared. Surprisingly they did not show photochromism. However, they readily underwent a tandem addition of a nucleophile and an electrophile, leading to a small library of dearomatized colourless analogues, which, on the contrary, were endowed with photochromic activity. In the absence of the electrophile, the intermediate obtained by C-attack readily aromatizes to give, surprisingly, a final product of direct aromatic nucleophilic substitution, which was not photochromically active. [ABSTRACT FROM AUTHOR]

Starting with the parent compound [2.2.2]paracyclophane several routes were developed to synthesize its 4-vinyl derivative. From the 4-aldehyde and the bromomethyl derivative the stilbenophanes were prepared which photocyclize to the phenanthrenophanes. A new route to a bridged ketone was developed which was subjected to the addition of phenyllithium and to typical aromatic substitution reactions (inter alia Rieche formylation, Friedel-Crafts acylation). Bromination of the bridged ketone yielded an unusual tropone derivative. Electrophilic substitution reactions were also carried out for the bridged hydrocarbon, the reduction product of the bridged ketone. For both the bridged ketone and the bridged hydrocarbon the electrophilic substitutions occur regioselectively, favoring the introduction of the new substituent in a syn orientation to the bridging keto and methylene group, respectively. [ABSTRACT FROM AUTHOR]

1-Benzoyl-1-( o-alkoxyphenyl)cyclopropanes undergo Yang photocyclization to form dihydrobenzo-pyranols in a stereospecific manner. The cyclopropyl group at alpha position to carbonyls gives not only a bias in the most stable geometries of the starting ketones but also conformational restriction on geometries of biradical intermediates. More importantly, intramolecular hydrogen bonds seem to give an additional effect on conformational control of the biradical reactivity. [ABSTRACT FROM AUTHOR]

A new polymerization method for in situ generation of luminescent polymers with aggregation-induced emission characteristics from readily prepared or commercially available reactants was developed in this work. The "1 + 2" polycoupling of internal alkynes and arylboronic acids took place under mild reaction conditions and was tolerant to moisture, air, and monomer stoichiometric imbalance, furnishing poly(hexaphenyl-1,3-butadiene)s (PHBs) with partially or wholly conjugated structures in satisfactory yields. All the PHBs showed good solubility, thermal stability, and film-forming ability. Their optical properties could be easily tuned by proper monomer design and external perturbation. The PHBs underwent active photocyclization in both solution and solid states, converting them to poly(dihydronaphthalene)s. Such a property made them promising materials for fabricating luminescent photopatterns. A new mechanistic pathway was proposed as supplementary to explain the aggregation-induced emission (AIE) phenomenon by studying the emission of PHBs and the corresponding model compound. [ABSTRACT FROM AUTHOR]

Benzo[ h ]-naphth[1,2- f ]quinazolines and benzo[ h ]-phenanthren[9,10- f ]quinazoines were synthesized from intermediates 4-(2-hydroxyphenyl)-5-(naphthalen-1-yl)pyrimidines and 4-(2-hydroxyphenyl)-5-(phenanthren-1-yl) pyrimidines by the intramolecular dehydration of photocyclization. The intermediates were obtained by the condensation of 3-arylchromone with formamidine, acetamidine or guanidine refluxing in ethanol, respectively. Irradiation of the corresponding intermediates by a high-pressure mercury lamp in 19:1 (v/v) EtOH H 2 O or 18:1:1 (v/v) EtOH H 2 O-Dioxane lead to target products. This photocyclization showed advantages including catalyst-free and mild reaction condition. Moreover, water was the only by-product of this reaction. The crystal structure of 2-amino-12-methoxy-benzo[ h ]-naphth[1,2- f ]quinazoline was determined and the fluorescence properties of these polybenzoquinazolines were also investigated. [ABSTRACT FROM AUTHOR]

Three new diruthenium oxyanion complexes have been prepared, crystallographically characterized, and screened for their potential to photochemically unmask a reactive Ru--Ru = 0 intermediate. The most promising candidate, Ru2(chp)4ONO2 (4, chp = 6-chloro-2-hydroxypyridinate), displays a set of signals centered around m/z = 733 amu in its MALDI-TOF mass spectrum, consistent with the formation of the [Ru2(chp)4O]+([6]+) ion. These signals shift to 735 amu in 4*, which contains an lsO-labeled nitrate. EPR spectroscopy and headspace GCMS analysis indicate that NO2* is released upon photolysis of 4, also consistent with the formation of 6. Photolysis of 4 in CH2C12 at room temperature in the presence of excess PPh3 yields OPPh3 in 173% yield; control experiments implicate 6, NO2*, and free NO3- as the active oxidants. Notably, Ru2(chp)4Cl(3) is recovered after photolysis. Since 3 is the direct precursor to 4, the results described herein constitute the first example of a synthetic cycle for oxygen atom transfer that makes use of light to generate a putative metal oxo intermediate. [ABSTRACT FROM AUTHOR]

A rhodamine-modified diarylethene was designed and synthesised which could respond to both pH and irradiation in a synergic manner. This molecule shows neither fluorescence nor photochromism in neutral or alkaline aqueous solution (pH ≥ 7). When the pH is decreased, fluorescence of the molecule is dramatically enhanced and the photochromic reactivity is unlocked. In the pH range of 1.0–4.0, the emission intensity of the rhodamine unit in the molecule can be remotely controlled by UV (360 nm) and visible light (670 nm) irradiation. Thus the switch of the fluorescence and photochromic properties of the molecule can be synergistically operated by proton and light irradiation. [ABSTRACT FROM AUTHOR]

Light-induced transformation of atropisomeric and achiral enones displays divergent reactivity. Photocyclization leading to 3,4-dihydroquinolin-2-one was observed with achiral enone carboxamide, whereas the atropisomeric enone carboxamides underwent hydrogen abstraction leading to spiro-β-lactams. Detailed photochemical, photophysical, and theoretical investigations have provided insight into this divergent reactivity and selectivity. [ABSTRACT FROM AUTHOR]

Photolysis of 1-arylthio-2-azidoanthraquinones in DMSO in the presence of phenols leads to the formation of 5 H-naphtho[2,3- c]phenothiazine-8,13-diones, in which the nitrogen atom is covalently bonded with the phenyl ring of the introduced phenol. As a result, poorly available polycyclic phenothiazine derivatives were obtained in one step in high yields. The cyclo-condensation with phenols was found to proceed only photochemically. [ABSTRACT FROM AUTHOR]

Bis[2,4-di(trifluoromethyl)quinoline-7-yl]amine (1), bis[2,4-di(trifluoromethyl)quinoline-7-yl]methylamine (2), bis[2,4-di(trifluoromethyl)quinoline-7-yl]phenylamine derivatives, Q2NPhX; X=NO2 (3 a), I (3 b), H (3 c), OMe (3 d), and NH2 (3 e), tris[2,4-di(trifluoromethyl)quinoline-7-yl]amine (4), and bis[2,4-di(pentafluoroethyl)quinoline-7-yl]-4-nitrophenylamine (5) were prepared as functional fluorophores. On irradiating the solution samples, 1 showed no noticeable alteration, whereas 2, 3 a-d, and 4 showed emission color changes from yellowish green to blue, indicating that a photoreaction took place. Analyses of the photoproduct based on absorption and emission spectra, ¹H NMR spectra, and X-ray crystallography indicated that photocyclization reactions occurred regioselectively and quantitatively to form bent-bent dipyridocarbazoles. In 3 a-d, the reaction rates depended on the solvent polarity and the substituent on the benzene ring. The photoreactions were accelerated with decreasing solvent polarity and with increasing electron-withdrawing character of the substituents. The photocyclization of triquinolineamine 4 was faster than that of 3 a in all solvents. The results of semiempirical quantum-chemical PM6 calculations suggested that the observed regioselective photocyclization could be explained by stabilization of the excited triplet transition state for the bent-bent form because of the molecular geometry with the CH-NQ hydrogen bonds. The solution of 5 in MeOH displayed photoreaction-induced self-assembly behavior to form twisted tape-like fibers of width 200 nm, as determined by TEM imaging. [ABSTRACT FROM AUTHOR]

Synthetic organic photochemistry is a field that continues to offer unique routes to organic structures not typically accessed from thermal reactions. In this review, the photochemical synthesis of five-, six-, seven-, and eight-membered-ring azaheterocycles, as well as some aza-macrocycles, is discussed. The discussion will focus on methods where heterocycle formation occurs during or as a result of a photochemical event. Reaction mechanisms will be discussed also, as these provide a rationale for understanding the synthetic results. 1 Introduction 2 Five-Membered Rings 2.1 Cyclization Reactions 2.2 Cycloadditions 2.3 From Aromatic and Vinyl Azides 2.4 earrangements 2.5 Other Individual Methods 3 Six-Membered Rings 3.1 Cyclization Reactions 3.2 Isocyanide Insertions 3.3 Cycloadditions 4 Seven-Membered Rings and Larger 5 Conclusion. [ABSTRACT FROM AUTHOR]

An unusual H /D kinetic isotope effect (KIE) is described, in which isotopic selectivity arises primarily from nonstatistical dynamics in the product. In DFT-based quasiclassical trajectories of Bergman cyclization of (Z)-3-hexen-l,5-diyne ( l ) at 470 K, the new CC bond retains its energy, and 28% of nascent p-benzyne recrosses back to the enediyne on a vibrational time scale. The competing process of intramolecular vibrational redistribution (IVR) in p-benzyne is too slow to prevent this. Deuteration increases the rate of IVR, which decreases the fraction of recrossing and increases the yield of statistical (trapable) p-benzyne, 2. Trapable yields for three isotopomers of 2 range from 72% to 86%. The resulting KIEs for Bergman cyclization differ substantially from KIEs predicted by transition state theory, which suggests that IVR in this reaction can be studied by conventional KIEs. Leakage of vibrational zero point energy (ZPE) into the reaction coordinate was probed by trajectories in which initial ZPE in the CH/CD stretching modes was reduced by 25%. This did not change the predicted KIEs. [ABSTRACT FROM AUTHOR]

A short and efficient synthesis leading to a new helically chiral heptacyclic system, containing a carbazole unit, was achieved via a Knoevenagel condensation–photocyclization strategy. The optical properties of the carbazole-based material were investigated by UV–vis absorption and photoluminescence spectroscopy and an emission in the visible region was observed. From the cyclic voltammetry analysis, the electrochemical band gap of the target organic material was estimated to be 2.38 eV indicating that it might be a good candidate for electron-injection hole-blocking layers in organic light-emitting diodes. [ABSTRACT FROM AUTHOR]

The twofold glyoxylic Perkin reaction of perylene-3,9-diglyoxylic acid with thiophene-diacetic acid followed by oxidative photocylization and reaction with α-branched primary alkylamines yields columnar liquid-crystalline diimides with two sulfur atoms in the condensed arene system. A broad temperature range of the hexagonal columnar mesophase is induced by racemic doubly branched alkyl chains. The HOMO and LUMO energy levels of these thiophene-derived diimides qualify them as electron donors with respect to perylene diimides. [ABSTRACT FROM AUTHOR]

Bis[2,4-di(trifluoromethyl)quinoline-7-yl]amine ( 1), bis[2,4-di(trifluoromethyl)quinoline-7-yl]methylamine ( 2), bis[2,4-di(trifluoromethyl)quinoline-7-yl]phenylamine derivatives, Q2NPhX; X=NO2 ( 3 a), I ( 3 b), H ( 3 c), OMe ( 3 d), and NH2 ( 3 e), tris[2,4-di(trifluoromethyl)quinoline-7-yl]amine ( 4), and bis[2,4-di(pentafluoroethyl)quinoline-7-yl]-4-nitrophenylamine ( 5) were prepared as functional fluorophores. On irradiating the solution samples, 1 showed no noticeable alteration, whereas 2, 3 a- d, and 4 showed emission color changes from yellowish green to blue, indicating that a photoreaction took place. Analyses of the photoproduct based on absorption and emission spectra, 1H NMR spectra, and X-ray crystallography indicated that photocyclization reactions occurred regioselectively and quantitatively to form bent-bent dipyridocarbazoles. In 3 a- d, the reaction rates depended on the solvent polarity and the substituent on the benzene ring. The photoreactions were accelerated with decreasing solvent polarity and with increasing electron-withdrawing character of the substituents. The photocyclization of triquinolineamine 4 was faster than that of 3 a in all solvents. The results of semiempirical quantum-chemical PM6 calculations suggested that the observed regioselective photocyclization could be explained by stabilization of the excited triplet transition state for the bent-bent form because of the molecular geometry with the CH−NQ hydrogen bonds. The solution of 5 in MeOH displayed photoreaction-induced self-assembly behavior to form twisted tape-like fibers of width 200 nm, as determined by TEM imaging. [ABSTRACT FROM AUTHOR]

Photoirradiation of the titled compounds perfluoro- cis -1,2-dimethyl-butadienyl benzenes ( 1 ), which were prepared in several steps from perfluorovinyl bromide, results in the formation of the corresponding novel naphthalene derivatives and 1,4-dihydronaphthalenes. Isolated 1,1,2-trifluoro-3,4-bis(trifluoromethyl)-1,4-dihydronaphthalene ( 3a ) could be converted into 1,2-bistrifluoromethyl-3,4-difluoronaphthalene ( 2a ) by base treatment (DABCO); however, 3a did not lead to 2a by photoreaction, suggesting 3a was not a possible photochemical precursor. Competitive photoreaction studies suggest that varying the substituent on benzene ring (e.g. methyl or trifluoromethyl) does not significantly affect the reaction rate. Presently, this reaction mechanism is not yet clearly understood. [ABSTRACT FROM AUTHOR]

A mechanism for integrating light perception and the endogenous circadian clock is central to a plant's capacity to coordinate its growth and development with the prevailing daily light/dark cycles. Under short-day (SD) photocycles, hypocotyl elongation is maximal at dawn, being promoted by the collective activity of a quartet of transcription factors, called PIF1, PIF3, PIF4, and PIF5 (phytochromeinteracting factors). PIF protein abundance in SDs oscillates as a balance between synthesis and photoactivated-phytochrome-imposed degradation, with maximum levels accumulating at the end of the long night. Previous evidence shows that elongation under diurnal conditions (as well as in shade) is also subjected to circadian gating. However, the mechanism underlying these phenomena is incompletely understood. Here we show that the PIFs and the core clock component Timing of CAB expression 1 (TOC1) display coincident cobinding to the promoters of predawn-phased, growthrelated genes under SD conditions. TOC1 interacts with the PIFs and represses their transcriptional activation activity, antagonizing PIF-induced growth. Given the dynamics of TOC1 abundance (displaying high postdusk levels that progressively decline during the long night), our data suggest that TOC1 functions to provide a direct output from the core clock that transiently constrains the growth-promoting activity of the accumulating PIFs early postdusk, thereby gating growth to predawn, when conditions for cell elongation are optimal. These findings unveil a previously unrecognized mechanism whereby a core circadian clock output signal converges immediately with the phytochrome photosensory pathway to coregulate directly the activity of the PIF transcription factors positioned at the apex of a transcriptional network that regulates a diversity of downstream morphogenic responses. [ABSTRACT FROM AUTHOR]

Two novel perfluorodiarylethenes which contains a 2-methylbenzo[b]furane and a modified pyridine moiety were synthesized. Such structure may induce F⋯N or S⋯N heteroatom contact which was newly observed. Experiments results showed that the photocyclization quantum yield exhibited a strong correlation with the two weak intramolecular interactions, which behaved solvent independency. Moreover, both novel pyridine-perfluorodiarylethenes exhibited an obvious acidichromism, and the absorption maxima of their closed-ring isomers showed a prominent bathochromic shift to the near-infrared region. [ABSTRACT FROM AUTHOR]

A convenient synthetic route to novel 7-substituted benzo[ f]thieno[3,2- h]quinazoline and 8-substituted benzo[ g, h]dithieno[2,3- e:3′,2′- j]perimidine systems, bearing the fused pyrimidine ring, has been advanced. A commercially available 5-bromopyrimidine was used as the starting material to obtain various polycyclic systems through the sequence of nucleophilic aromatic substitution of hydrogen (the SNH reaction), Suzuki cross-coupling and oxidative photocyclization. Evidence for the structure of benzo[ g, h]dithieno[2,3- e:3′,2′- j]perimidines has been obtained by X-ray crystallographic analysis. Molecular orbital calculations (DFT), as well as redox and optical measurements for all new compounds have been performed. The data show that the reported polycyclic systems have potential for use in organic electronic applications. [ABSTRACT FROM AUTHOR]

Six difluoroboronated β-diketones having the phenanthrene skeleton (Phe@Ar) are prepared. Based on the measurements of the fluorescence quantum yields, lifetimes and transient absorption, the photophysical features of Phe@Ar are studied in comparison with those of difluoroboronated diketones having phenyl, naphthyl and anthryl moieties. β-Diketones having 1-, 2-, 3- and 9-phenanthryl moieties (PheDKAr) were prepared as the precursor to Phe@Ar. 1-Acetylphenanthrene was synthesized by the photocyclization method as the key building block of PheDKAr having the 1-phenanthryl moiety. The counter aromatic moieties (Ar) of the prepared PheDKAr are varied with phenyl, furyl and thienyl rings (Ar = Ph, F and T, respectively) to investigate the effects of π-conjugation on the fluorescence properties. The prepared Phe@Ars are fluorescent with appreciable fluorescence quantum yields which depend on the substitution position of the phenanthrene moiety. 3-Phe@Ph having the 3-phenanthryl moiety provides the largest fluorescence quantum yield (0.81) in acetonitrile among the Phe@Ars whereas 2-Phe@Ph having the 2-phenanthryl moiety shows the smallest fluorescence quantum yield (0.07) in acetonitrile. All the Phe@Ars show fluorescence also in the solid state, and the fluorescence spectra and quantum yields were determined. Transient absorption measurement using laser flash photolysis of the Phe@Ars revealed the triplet formation. DFT and TD-DFT calculations of Phe@Ars rationalize the dependency of the fluorescence quantum yields on the substitution position of the phenanthrene skeleton in terms of difference in the oscillator strength for the HOMO–LUMO transition. [ABSTRACT FROM AUTHOR]

One of the key concerns with the development of radical-generating reactive therapeutics is the ability to control the activation event within a biological environment. To that end, a series of quinoline–metalloenediynes of the form M( QuiED )·2Cl (M = Cu(II), Fe(II), Mg(II), or Zn(II)) and their independently synthesized cyclized analogs have been prepared in an effort to elucidate Bergman cyclization (BC) reactivity differences in solution. HRMS(ESI) establishes a solution stoichiometry of 1:1 metal to ligand with coordination of one chloride counter ion to the metal center. EPR spectroscopy of Cu( QuiED )·2Cl and Cu( QuiBD )·2Cl denotes an axially-elongated tetragonal octahedron ( g || > g ⊥ > 2.0023) with a d x 2 - y 2 ground state, while the electronic absorption spectrum reveals a pπ Cl→Cu(II) LMCT feature at 19,000 cm −1 , indicating a solution structure with three nitrogens and a chloride in the equatorial plane with the remaining quinoline nitrogen and solvent in the axial positions. Investigations into the BC activity reveal formation of the cyclized product from the Cu(II) and Fe(II) complexes after 12 h at 45 °C in solution, while no product is observed for the Mg(II) or Zn(II) complexes under identical conditions. The basis of this reactivity difference has been found to be a steric effect leading to metal–ligand bond elongation and thus, a retardation of solution reactivity. These results demonstrate how careful consideration of ligand and complex structure may allow for a degree of control and selective activation of these reactive agents. [ABSTRACT FROM AUTHOR]

The photochemical behavior of terarylenes containing furan and allomaltol fragments was studied. It was demonstrated that starting 2-aminofurans containing 3-hydroxypyran-4-one moiety did not undergo any transformations under UV-irradiation. We supposed that all photoreactions are blocked due to the presence of amino group in the structure of the studied terarylenes. Wherein, the conversion of the amino group into pyrrole unit in the considered compounds allows one to unlock both 6π-electrocyclization of the 1,3,5-hexatriene system and ESIPT-promoted processes. At the same time, subsequent methylation of the hydroxyl group of allomaltol fragment leads to regiospecific photocyclization of terarylene core due to the suppression of ESIPT-induced reactions. Thus, UV-irradiation of methylated pyrrole-containing products results in 6π-electrocyclization of the 1,3,5-hexatriene system with the formation of polyaromatic compounds. Alternatively, ESIPT-promoted contraction of allomaltol moiety was observed in the cases when aforementioned 6π-electrocyclization is impossible. The structures of two synthesized products were established by X-ray diffraction. To create your abstract, type over the instructions in the template box below. Fonts or abstract dimensions should not be changed or altered. [Display omitted] • The photochemical behavior of terarylenes with furan and allomaltol units was studied. • UV-induced regiospecific 6π-electrocyclization of the terarylenes was shown. • Efficient method for the preparation of benzo [ f ]furo [2,3- h ]chromenes was suggested. • ESIPT-promoted contraction of allomaltol moiety was observed. • The structures of two synthesized products were established by X-ray diffraction. [ABSTRACT FROM AUTHOR]

The conical intersection (CI) governs the ultra-fast relaxation of excited states in a radiationless manner and are observed mainly in photochemical processes. In the current work, we investigated the effects of substituents on the reaction dynamics for the conversion of gauche-1,3-butadiene to bicyclobutane via photochemical electrocyclization. We incorporated both electron withdrawing (-F) and donating (-CH 3 ) groups in the conjugated system. In our study, we optimized the minimum energy conical intersection (MECI) geometries using the multi-configurational state-averaged CASSCF approach, whereas, to study the ground state reaction pathways for the substituted derivatives, dispersion corrected, B3LYP-D3 functional was used. The non-adiabatic surface hopping molecular dynamics simulations were performed to observe the behaviour of electronic states involved throughout the photoconversion process. The results obtained from the multi-reference second-order perturbation correction of energy at the XMS-CASPT2 level of theory, topography analysis, and non-adiabatic dynamics suggest that the -CH 3 substituted derivatives can undergo faster thermal conversion to the product in the ground state with a smaller activation energy barrier compared to -F substituted derivative. Our study also reveals that the GBUT to BIBUT conversion follows both conrotatory and disrotatory pathways, whereas, on substitution with -F or -CH 3 , the conversion proceeds via the conrotatory pathway., (© 2022 Wiley-VCH GmbH.)

The triplet sensitized cyclization of enyne-carbodiimide 4 leads to efficient formation of indoloquinoline 5 with concomittant loss of a methyl group. The efficient loss of the methyl group was explained using AM1 semiempirical calculations.

In the present study, we have investigated different strategies for diastereoselective synthesis of thia[n]- helicenes. We describe the introduction of different chiral auxiliaries at various positions and investigated their effect in the photocyclization reaction. Different chiral groups were placed at the sterically hindered position of the helical core and their interactions with various solvents and metals like copper were investigated. The use of CuI salts has led to high diastereoselectivity in the photocyclization process and we were successful in obtaining the thia[5]helicene in enantiomerically pure form in good yield. The single diastereomer obtained was characterized by X-ray crystallography. From the study of the barrier of racemization of these thia[5]-helicenes, the stability was found to be comparable to unsubstituted tetrathia[7]helicenes and substituted diazadithia[ 7]helicenes. This approach provides an easy access to enantiopure helicenes. [ABSTRACT FROM AUTHOR]

Anion binding of adamantane bisurea receptors 1 – 4 bearing anthracene chromophores was investigated in DMSO solution by UV–vis and fluorescence titrations. All derivatives form stable complexes with F − (K 1:2 ≈10 5 –10 6 M −2 ), AcO − (K 1:1 ≈10 3 M −1 ), and H 2 PO 4 − (K 1:1 ≈10 3 –10 4 M −1 , K 1:2 ≈10 5 –10 6 M −2 ). Photochemical reactivity of 1 – 4 in the [4π+4π] photocyclizations was also investigated. Anthracene 1 is photochemically stable, 3 and 4 undergo reaction giving mixture of products, but 2 reacts selectively yielding only cyclic product 5 . Product 5 was isolated and characterized by X-ray analysis. Cyclic receptor 5 also binds anions but forms complexes with different stability constants than its opened analogue 2 . Anthracene 2 forms more stable complex with H 2 PO 4 − , whereas cyclic receptor 5 forms the most stable complex with AcO − (K 1:1 >10 6 M −1 ). [ABSTRACT FROM AUTHOR]

The phototransformation of some 2-(3-methoxyphenyl)-4H-chromen-4-ones bearing a propynyloxy moiety at the 3-position has been described. On photolysis with pyrex-filtered UV light from a Hg lamp (125 W), these chromenones produced a major amount of 5-ethynyl-2-methoxy-6-oxa-benzo[5,6-c]xanthen-7-ones consisting of an exotic tetracyclic scaffold. These photoproducts have been envisioned to be produced through regioselective ring closure at the 6′-position of the 2-(3′-methoxy)phenyl moiety of the initially formed 1,4-biradical via a γ-H abstraction mechanism. No product whatsoever was observed through ring closure at the 2′-position. This behaviour has been found to be in accordance with the directive influence observed in free radical aromatic substitutions. This regioselective photocyclisation is further supported by calculations made from 3D structures (MM2 program). In addition, during the irradiation of these substrates, 2-(3-methoxyphenyl)-4H-chromen-4-ones were also realised through dealkoxylation. The structures of the substrates and photoproduct(s) have been determined by their spectroscopic (IR, NMR, mass spectrometry) studies. [ABSTRACT FROM AUTHOR]

Novel terpyridine 1 was synthesized via Suzuki coupling; the resulting series of asymmetric conjugated terpyridine moieties were produced in good yield through subsequent UV irradiation. Oxidative cyclodehydrogenation was confirmed through isolation of the intermediate, proving the zippering cyclization in association with the aromatic conjugation expansion. The stepped conjugation could be controlled by choosing an appropriate solvent. The dimerization of terpyridine 1 was successfully introduced, making headway for these highly conjugated organometallic systems. [ABSTRACT FROM AUTHOR]

New helically chiral heptacyclic systems with cyano groups at selected positions have been synthesized in good yields, via a four-step sequence, from readily available materials. The optical properties of the target helicenes were investigated by UV–visible absorption and photoluminescence spectroscopy and an emission in the visible region was observed. The energy levels of these organic materials were determined by cyclic voltammetry and showed a relatively high electronic affinity, indicating that they may be good candidates for electron-injection hole blocking layer in organic light-emitting diodes. [ABSTRACT FROM AUTHOR]

A series of five benzannelated derivatives of 2-phenylphenol were prepared, and their photochemistry was investigated. Two of these (3-phenyl-2-naphthol, 10, and 1-phenyl-2-naphthol, 11) were photoinert. For 2-(1-naphthyl)phenol (12) and 1-(1-naphthyl)-2-naphthol (13), ESPT took place to either the 2′-position or the 7′-position of the naphthalene ring to give quinone methides (QMs) that underwent either reverse proton transfer (RPT) or electrocyclic ring closure to give dihydrobenzoxanthenes. The intermediate QMs for 12 and 13 were detected and characterized by laser flash photolysis. For 2-(9-phenanthryl)phenol (14), ESPT took place either to the 5′-position to give a QM that underwent quantitative electrocyclic ring closure to give the corresponding benzoxanthene or to the 10′-position to give a QM that underwent RPT. If the solution contained methanol, the QM produced on ESPT to the 10′-position in 14 could be trapped as the photoaddition product. The compounds studied in this work demonstrate three possible reactions of QMs produced following ESPT to aromatic carbon atoms: (1) reverse proton transfer (RPT) to regenerate starting material; (2) addition of hydroxylic solvents to give the photoaddition product; and (3) electrocyclic ring closure to give benzoxanthene derivatives. [ABSTRACT FROM AUTHOR]

Polybrominated diphenyl ethers (PBDEs) and hydroxylated PBDEs can transform into polybrominated dibenzofurans (PBDFs) via photocyclization. However, it is unclear whether methoxylated PBDEs (MeO-PBDEs) can photocyclize to form MeO-PBDFs. In this study, 5-MeO-BDE-47, 5′-MeO-BDE-99 and 6-MeO-BDE-85 were selected as models to investigate their direct photolysis, especially photocyclization in two solvent environments (water and methanol) using simulated photochemical experiments and density functional theory (DFT) calculations. The experimental results showed that MeO-PBDEs had faster direct photolysis reactions and higher quantum yields in methanol, and MeO-PBDFs could only be formed in a methanol solution of 5-MeO-BDE-47. The DFT results indicated that the lowest excited triplet state MeO-PBDEs can form dibenzofurans via direct cyclization pathways. Intra-annular H-elimination was found to be the rate-determining step for most cyclization pathways with high reaction barriers (⩾19.7 kcal/mol), while 5-MeO-BDE-47 was found to have a distinct pathway for which the rate-determining step is ring closure with a low barrier (13.8 kcal/mol) in a methanol environment. For this pathway, H-elimination assisted by Br cleaved from an ortho -C–Br bond was observed with a 2.0 kcal/mol barrier. Thus, the DFT results reasonably explained the experimental findings, and the photocyclization of MeO-PBDEs depended on the specific Br-substitution patterns and specific effects of the environmental media. [ABSTRACT FROM AUTHOR]

Although many crystal structures of microbial rhodopsins have been solved, those with sufficient resolution to identify the functional water molecules are very limited. In this study, the Acetabularia rhodopsin I (ARI) protein derived from the marine alga A. acetabulum was synthesized on a large scale by the Escherichia coli cell-free membrane-protein production method, and crystal structures of ARI were determined at the second highest (1.52-1.80 Å) resolution for a microbial rhodopsin, following bacteriorhodopsin (BR). Examinations of the photochemical properties of ARI revealed that the photocycle of ARI is slower than that of BR and that its proton-transfer reactions are different from those of BR. In the present structures, a large cavity containing numerous water molecules exists on the extracellular side of ARI, explaining the relatively low p Ka of Glu206ARI, which cannot function as an initial proton-releasing residue at any pH. An interhelical hydrogen bond exists between Leu97ARI and Tyr221ARI on the cytoplasmic side, which facilitates the slow photocycle and regulates the p Ka of Asp100ARI, a potential proton donor to the Schiff base, in the dark state. [ABSTRACT FROM AUTHOR]

Microwave-promoted cyclocondensation of isoflavones with 3-amino[1,2,4]triazole gave 6-phenyl-7-(2-hydroxyphenyl)-1,2,4triazolo[ 4,3-a]pyrimidines as intermediates. Subsequent photocyclization of these intermediates delivered dibenzo[f,h][1,2,4]triazolo[3,4- b]quinazolines as final products. Water was the only by-product in this two-step procedure. The products showed distinct fluorescence properties both in solution and in the solid state. [ABSTRACT FROM AUTHOR]

A novel type of photocyclization of α-ketoamides was developed, affording unique cyclopropanols bearing amide functionality. N - tert -Butyl, N -trityl, or N -non-substituted α-ketoamides with a bulky substituent at the β-position of the amide functionality were efficiently converted to corresponding cyclopropanols through the activation of the γ-C H bond followed by C C bond formation between the α- and γ-positions of the amide. Hydrogen abstraction from the γ-position of the amide was considered to be the rate-determining step of cyclopropanol formation, based on the kinetic isotope effect. Cyclopropanols could be converted to two different types of functionalized α-ketoamides depending on the method of ring-opening. [ABSTRACT FROM AUTHOR]

Mallory-type photocyclization involves a series of photoreactions of stilbenes, o-terphenyls and related derivatives, which undergo intramolecular cyclization via dihydrophenanthrene intermediates. In typical Mallory photocyclizations, oxidants are usually needed to produce the final phenanthrene-containing product. In the research described here, appropriately fluorinated stilbenes and o-terphenyls undergo ring closure and HF is eliminated. This photocyclodehydrofluorination (PCDHF) reaction is very useful to produce a wide range of selectively fluorinated polynuclear aromatic hydrocarbons that possess a phenanthrene (or heterocyclic analogue of phenanthrene) substructure. These fluorinated products are of great interest in various aspects of the materials science. [ABSTRACT FROM AUTHOR]

Stimuli responsive compounds and materials are of high interest in synthetic chemistry and materials science, with light being the most intriguing stimulus due to the possibility to remote control the physicochemical properties of a molecule or a material. There is a constant quest to design photoswitches with improved switching efficiency and especially diarylethene-type switches promise photo cyclization quantum yields up to unity. However, only limited attention has been paid towards the influence of the solution conformation on the switching efficiency. Here, we describe a detailed NMR spectroscopic investigation on the conformational distribution of bridge-substituted dithienylcyclopentenes in solution. We could discriminate between several photoactive and photoinactive as well as two diastereomorphous conformations and show that the trends observed in the switching efficiency match the conformer populations obtained from state of the art NMR parameters in solution. [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]

Synthesis of two derivatives of bi-aza[ n ]helicenes is achieved by I 2 -THF mediated photocyclization of corresponding bi-styryl derivatives. The cyclization furnished the desired angularly fused bi-aza[5]helicene and bi-aza[6]helicene in moderate yields. The structures are established by NMR spectroscopy and single crystal X-ray analysis. The crystal structure indicate an unusually planer central biphenyl unit in the bi-aza[6]helicene. It also indicates to the presence of ‘ P ’ and ‘ M ’ stereoisomer in the bi-aza[6]helicene making it a meso isomer. The series of synthesized bi-aza[ n ]helicenes were characterized by UV and fluorescence spectroscopy. [ABSTRACT FROM AUTHOR]

The high reactivity of 6π-electrocyclization in polar solvents has remained one of the important challenges for diarylethenes because of the emergence of a twisted intramolecular charge transfer (TICT) state at the excited state in such polar media, which usually quenches the photocyclization reaction. Herein we report on the preparation and highly efficient photocyclization of 2,3-diarylbenzo[ b]thiophenes with nonsymmetric side-aryl units in a polar solvent. While the dithiazolylbenzo[ b]thiophene showed a suppressed quantum yield of 6π-electrocyclization of 54 % in methanol, the replacement of a thiazole unit with a thiophene ring led to a photon-quantitative 6π-cyclization reaction. The nonsymmetrical modification into the side-aryl units was considered to enhance the CH/π interactions between side-aryl units to support a photoreactive conformation in methanol. The stabilization of the photochromic reactive conformation is expected to suppress the formation of the TICT state at the excited state, leading to highly efficient photoreactivity. [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]

The recently discovered photoheterocyclization of a mixture of mixed phosphonium-iodonium ylides and acetylene compounds to give λ-phosphinoline, a new phosphorus-containing heterocycle, occurs with self-acceleration and an induction period at relatively high concentrations of the reactants. The reaction was found to be catalyzed by the acid formed during photolysis. We developed a spectrophotometric method to study the kinetics of photocyclization between phenylacetylene and a phosphonium-iodonium ylide in the presence of trifluoroacetic acid and studied how the yield of target λ-phosphinoline and kinetic parameters of the reaction, such as the induction period and maximum rate of product formation, depend on the initial concentrations of the starting compounds and catalyst. It was shown that the addition of the acid has no effect on the critical character of the dependence of the reaction on the concentration of the starting compound: the reaction proceeds only at an ylide concentration of >0.02 mol/L in a microheterogeneous suspension and the self-accelerating character of λ-phosphinoline formation is preserved. The optimum reagent ratios maximizing the yield of the target product were determined. The acid was found to play a dual role: it catalyzes the reaction only at concentrations not higher than the initial ylide concentration. At higher acid concentrations, no formation of λ-phosphinoline was observed. [ABSTRACT FROM AUTHOR]

Cyanobacteriochromes (CBCRs) are cyanobacterial photosensory proteins distantly related to phytochromes. Like phytochromes, CBCRs reversibly photoconvert between a dark-stable state and a photoproduct via photoisomerization of the 15,16-double bond of their linear tetrapyrrole (bilin) chromophores. CBCRs provide cyanobacteria with complete coverage of the visible spectrum and near-ultraviolet region. One CBCR subfamily, the canonical red/green CBCRs typified by AnPixJg2 and NpR6012g4, can function as sensors of light color or intensity because of their great variation in photoproduct stability. The mechanistic basis for detection of green light by the photoproduct state in this subfamily has proven to be a challenging research topic, with competing hydration and trapped-twist models proposed. Here, we use 13C-edited and 15N-edited ¹H-¹H NOESY solution nuclear magnetic resonance spectroscopy to probe changes in chromophore configuration and protein-chromophore interactions in the NpR6012g4 photocycle. Our results confirm a C15-Z,anti configuration for the red-absorbing dark state and reveal a ClS-E,anti configuration for the green-absorbing photoproduct. The photoactive chromophore D-ring is located in a hydrophobic environment in the photoproduct, surrounded by both aliphatic and aromatic residues. Characterization of variant proteins demonstrates that no aliphatic residue is essential for photoproduct timing. Taken together, our results support the trapped-twist model over the hydration model for the red/green photocycle of NpR6012g4. [ABSTRACT FROM AUTHOR]

We herein propose a new type of efficient neutral photoacid generator. A photoinduced 6π-electrocyclization reaction of photochromic triangle terarylenes triggers subsequent release of a Bronsted acid, which took place from the photocyclized form. A H-atom and its conjugate base were introduced at both sides of a 6π-system to form the self-contained photoacid generator. UV irradiation to the 6π-system produces a cyclohexa-1,3-diene part with a H-atom and a conjugate base on the sp³ C-atoms at 5- and 6-positions, respectively, which spontaneously release an acid molecule quantitatively forming a polyaromatic compound. A net quantum yield of photoacid generation as high as 0.52 under ambient conditions and a photoinitiated cationic polymerization of an epoxy monomer are demonstrated. [ABSTRACT FROM AUTHOR]