Photocyclization Reaction Research Articles

Studies toward the Photochemical Synthesis of Functionalized [5]- and [6]Carbohelicenes

An efficient route to nonsymmetrical helical menthyl esters by means of an oxidative photocyclization reaction of dissymmetric bis-stilbenes is reported. The developed route allows the introduction of functionality on rings A, E, or F, and the influence of the substituent pattern on the photochemical reaction has been examined. Diastereoselectivity is observed when a double chiral induction strategy with dimenthyl helicene esters synthesized in a 70:30 ratio of isomers is used.

Photocyclization Reaction of Diarylethene−Perylenebisimide Dyads upon Irradiation with Visible (>500 nm) Light

Two types of fluorescent diarylethene−perylenebisimide dyads were synthesized and their photochromic performance was studied. The dyads showed an unexpected photochromic reactivity. The photocyclization reaction takes place upon irradiation with visible light (>500 nm), where the diarylethene unit has no absorption. Inferring from the excitation wavelength dependence and oxygen effect, the triplet states of the diarylethene unit are considered to play an essential role in the photocyclization reaction with visible (>500 nm) light.

Synthesis, Electronic Properties, and Reactivity of Phospholes and 1,1′‐Biphospholes Bearing 2‐ or 3‐Thienyl C‐Substituents

Two series of phospholes and 1,1'-biphospholes bearing either 2- or 3-thienyl substituents at the C atoms are prepared by using the Fagan-Nugent route. Their optical (UV/Vis absorption, fluorescence spectra) and electrochemical properties are systematically evaluated. Of particular interest, the first ever reported 3-thienyl-substituted phospholes exhibit higher LUMO levels than their 2-thienyl analogues, and show accordingly different physical properties. This study also reveals that the 1,1'-biphospholes exhibit sigma-pi conjugation. The phosphole and 1,1'-biphosphole derivatives bearing 3-thienyl substituents are characterized by X-ray diffraction study. The structure-property relationship established following the experimental data are fully supported by theoretical studies including time-dependent(TD)-DFT spectra. A photocyclization reaction performed on the thioxo- and oxophospholes having 3-thienyl substituents affords a novel ring-fused phosphole-thiophene derivative, which was characterized by an X-ray diffraction study. The structure and electronic properties of this novel dithienophosphole are discussed based on experimental and theoretical data.

Role of Arg123 in Light‐driven Anion Pump Mechanisms of pharaonis Halorhodopsin†

Halorhodopsin (HR) acts as a light-driven chloride pump which transports a chloride ion from the extracellular (EC) to the cytoplasmic space during a photocycle reaction that includes some photointermediates initiated by illumination. To understand the chloride uptake mechanisms, we focused on a basic residue Arg123 of HR from Natronomonas pharaonis (NpHR), which is the only basic residue located in the EC half ion channel. By the measurements of the visible absorption spectra in the dark and the light-induced inward current through the membrane, it was shown that the chloride binding and transport ability of NpHR completely disappeared by the change of arginine to glutamine. From flashphotolysis analysis, the photocycle of R123Q differed from that of wildtype NpHR completely. The response of the R123H mutant depended on pH. These facts imply that the positive charge at position 123 is essential for chloride binding in the ground state and for the chloride uptake under illumination. On the basis of the molecular structures of HR and the anion-transportable mutants of bacteriorhodopsin, the effects of the positive charge and the conformational change of the Arg123 side chain as well as the chloride-pumping mechanism are discussed.

Photochromic Diarylethene-Containing Ionic Liquids and N-Heterocyclic Carbenes

The design and synthesis of a series of photochromic diarylethene-containing Arduengo-type N-heterocyclic carbenes (NHCs) of gold(I), silver(I) and palladium(II) and their imidazolium salt precursors are reported. Reversible photochromic behavior was observed. The open form and the closed form also show different luminescence properties. The electronic and conformational/steric changes associated with the photocyclization and photocycloreversion reactions may open up new opportunities for the discovery of new classes of photochromic ligands and metal-containing materials and catalysts with photoswitchable functions and activities and regio-/enantioselectivities.

Synthesis and photochromic properties of thiophenophan-1-enes containing a polyether bridge

[2.n]Thiophenophan-1-ene derivatives containing a polyether bridge have been synthesized by the coupling reaction of bis(iodomethyl)dithienylethene with polyethylene glycols under high dilution conditions. All prepared [2.n]thiophenophan-1-enes were photochromic, as photocyclization of the open forms took place by UV irradiation to give a yellow solution of the closed form and their ring opening reactions occurred upon visible irradiation. There were significant differences in the quantum yields for the photocyclization reactions and the photo ring-opening reactions due to the difference in their structures since their electric properties are similar. The kinetic parameters of the thermal ring opening reaction of the closed forms of thiophenophan-1-enes were estimated and they were also dependent on their bridges.

Photochromic properties of terarylene derivatives having a π-conjugation unit on central aromatic ring

A series of terarylenes based on 4,5-bisbenzothienylthiazole have been synthesized, and their photochromic properties are studied both in solution and in the crystalline state. The substitution effect of the central aromatic ring on the photochromic reactivity were also studied. The introduction and expansion of the π-conjugated system at the 2-position of the thiazole ring led to a red-shift of the absorption peaks for both open- and closed-ring isomers of terarylenes. 2-Hydro and 2-phenyl derivatives of 4,5-bisbenzothienylthiazoles displayed a photochromic reaction, even in the single-crystal state. X-Ray crystal analysis showed their molecular structure to have quasi-C2 symmetry, suggesting significant CH⋯N and CH⋯S interactions. Although the 2-hydro and 2-phenyl derivatives exhibited high photocyclization reaction quantum yields over 0.5, the 2-phenylthienyl derivative showed a considerably smaller reactivity, even though it is supposed to have a similar conformation to those of the other two derivatives. Meanwhile, these molecules showed similar photocycloreversion quantum yields as high as 0.3. The relationship between their electronic structures and photochromic reactivity is also discussed by means of quantum chemical calculations.

9‐Bromoanthracene photodimers as initiators in controlled radical polymerization: Silane radical atom abstraction coupled with nitroxide mediated polymerization

AbstractSlow initiation relative to propagation has previously prevented photodimers of 9‐bromoanthracene or 9‐chloroanthracene, formed by [4 + 4] photocyclization reactions of the analogous 9‐haloanthracene, from being viable initiators in atom transfer radical polymerization (ATRP) reactions. The resulting polymers were found to possess high polydispersity index (PDI) values, much higher than expected number average molecular weight (Mn) values, with the reaction displaying a nonlinear relationship between monomer conversion and Mn. We report here the use of silane radical atom abstraction (SRAA) to create initiating bridgehead radicals in the presence of 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) to mediate the polymerization. When using SRAA coupled with nitroxide mediated polymerization, a dramatic decrease in PDI values was observed compared with analogous ATRP reactions, with Mn values much closer to those anticipated based on monomer‐to‐initiator ratios. Analysis using UV‐Vis spectroscopy indicated only partial anthracene labeling (∼ 25%) on the polymers, consistent with thermolysis of the anthracene photodimer coupled with competition between initiation from the bridgehead photodimer radical and silane‐based radical. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6016–6022, 2008

Crucial Role in Light Signal Transduction for the Conserved Met93 of the BLUF Protein PixD/Slr1694

PixD/Slr1694 from the cyanobacterium Synechocystis sp. PCC6803 is a member of a new class of flavin-containing blue-light sensory proteins containing a BLUF (blue light using flavin) domain. The photocycle reaction mechanism of BLUF is unique because only small structural changes of a bound chromophore are accompanied by a few hydrogen bond rearrangements in the chromophore-binding site. Here, we show that in PixD, Met93, the residue conserved in all BLUF domains, is crucial for light-dependent signal transduction. Specifically, the light-insensitive M93A mutant of PixD revealed biochemical and physiological activities compatible with those of the light-adapted wild-type PixD. However, the W91A mutant of PixD retained light sensitivity and biological function, although the corresponding mutant of another BLUF protein, AppA, has been reported to be locked in the light signaling state. These observations suggest that the pathway through which the light signal is transformed into apoprotein structural changes has been modified in BLUF proteins for their respective functions.

1-(2-Chloro-phen-yl)-2-(2-methyl-5-phenyl-3-thien-yl)-3,3,4,4,5,5-hexa-fluoro-cyclo-pent-1-ene: a new photochromic diaryl-ethene.

The title compound, C22H13ClF6S, is a hybrid diaryl­ethene derivative with one 3-thienyl substituent, and a Cl-substituted six-membered aryl unit bonded to the double bond of a hexa­fluoro­cyclo­pentene ring. In the crystal structure, the mol­ecule adopts a photo-active anti­parallel conformation that can undergo effective photocyclization reactions. The distance between the two reactive C atoms is 3.848 (3) Å. The dihedral angles between the least-squares cyclo­pentene plane and those of the adjacent thio­phene and chloro­phenyl rings are 49.39 (8) and 59.88 (8)°, respectively. The F atoms are disordered over two positions, with site occupancy factors of 0.6 and 0.4.

Photochemical properties of amino and nitro derivatives of 2-and 4-styrylquinolines and their hydrochlorides

The trans-cis and cis-trans photoisomerization reactions of a double bond in nitro and amino derivatives of 2-and 4-styrylquinolines in the neutral and protonated (hydrochloride) forms were studied. Protonation in nitrostyrylquinolines was shown to have no effect on the photoisomerization quantum yields. In aminostyrylquinolines, the photoisomerization reaction is “switched off” for the monocationic form as a result of the competitive process of intramolecular charge transfer and is “switched on” again for the dication. In the latter case, the quantum yield of trans-cis photoisomerization decreases by a factor of 2–2.5 and the quantum yield of cis-trans photoisomerization remains practically unchanged as compared to that of the neutral compound. Upon long-term irradiation of 4-(4′-nitrostyryl)quinoline, the photocyclization reaction of the cis-isomer was observed.

Lariat-crown ether based fluorescence sensors for heavy metal ions

Exploratory investigations were conducted to probe several aspects of a new strategy for the design of metal ion fluorescence sensors. The results of the investigation show that lariat-crown ethers that contain amine and thioether side chains, and a naphthalene chromophore can be efficiently prepared by using sequences that rely on key single electron transfer promoted photocyclization reactions. Members of this novel family of lariat-crown ethers serve as selective fluorescence sensors for the divalent metal cation of Mg, Hg, and Pb. The response of the sensors to the divalent metal ion is modulated by the nature of the heteroatom(s) incorporated into the side chains. Specifically, lariat-crown ethers that contain tertiary amine groups in their side chains display an off–on type response to Mg(II), Hg(II), and Pb(II). In contrast, thioether side chain containing lariat-crown ethers behave differently in that their fluorescence intensities decrease in the presence of increasing concentrations of these divalent metal cations. These responses can be understood on the basis of selective divalent metal ion induced disruption of intramolecular single electron transfer (SET)-quenching (for side chain amine containing lariat-crown ethers) and the enhancement of intersystem crossing (for side chain thioether containing lariat-crown ethers) of the singlet excited state of the naphthalene fluorophore.

The synthetic potential of pyridinium salt photochemistry

The discovery in the 1970s by Kaplan, Wilzbach and Pavlik that pyridinium salts undergo a unique cyclization reaction to produce bicyclic-aziridines was virtually unrecognized for nearly three decades. It was only comparatively recently that the process was explored in more detail and its synthetic potential exploited. In this Perspective, photocyclization reactions of pyridinium salts will be discussed, starting with the initial discovery, covering related processes of pyrylium salts, and extending to applications to the synthesis of natural and non-natural products of biomedical interest.

Photoregulated Fluorescence Switching in Axially Coordinated Tin(IV) Porphyrinic Dithienylethene

Photochromic fluorophore Sn(TTP)(DTE)2 , in which two phenolic derivatives of 1,2-dithienylethene are axially coordinated to (5,10,15,20-tetratolylporphyrinato)tin(IV) in trans position, has been synthesized and fully characterized by various spectroscopic methods. We have also investigated the photoregulated fluorescence switching behavior of Sn(TTP)(DTE)2 . The fluorescence of the porphyrin macrocycle in Sn(TTP)(DTE) 2 greatly depends on the state of the 1,2-dithienyletene photochromic switch. In the open state (Sn(TTP)(o-DTE)2), the porphyrin exhibits high fluorescence intensity at 609 and 664 nm when excited at 410 nm. When the photocyclization reaction was carried out by irradiating Sn(TTP)(o-DTE)2 with the UV light (approximately 365 nm), the fluorescence intensity of the porphyrin macrocycle decreased. Back irradiation with visible light at wavelengths greater than 500 nm regenerated Sn(TTP)(o-DTE)2 and almost restored the original fluorescence spectrum. The fluorescence intensity of the porphyrin fluorophore is efficiently regulated by photochromic switching between Sn(TTP)(o-DTE)2 and Sn(TTP)(c-DTE)2 in several cycles, clearly demonstrating that the Sn(TTP)(DTE)2 can act as a system for reversible data processing using fluorescence as the detection method.

Single Electron Transfer-Promoted Photocyclization Reactions of Linked Acceptor−Polydonor Systems: Effects of Chain Length and Type on the Efficiencies of Macrocyclic Ring-Forming Photoreactions of Tethered α-Silyl Ether Phthalimide Substrates

Results of an investigation, aimed at gaining information about the factors governing the efficiencies of single electron transfer (SET)-promoted photocyclization reactions of linked acceptor-polydonor systems, are described. One set of substrates used in this effort includes alpha-trimethylsilyl ether terminated, polymethylene- and polyethylenoxy-tethered phthalimides and 2,3-naphthalimides. Photocyclization reactions of the polyethylenoxy-linked phthalimides and naphthalimides were observed to take place in higher chemical yields and with larger quantum efficiencies than those of analogs containing polymethylene tethers of near equal length. These findings show that the rates of formation of 1,omega-zwitterionic biradicals that serve as key intermediates in the photocyclization processes are enhanced in substances that contain oxygen donor sites in the chain. The findings suggest that these donor sites facilitate both initial SET to acceptor excited states and ensuing intrachain SET, resulting in migration of the cation radical center to the terminal alpha-trimethylsilyl ether position. In addition, an inverse relationship was observed between the quantum yields of photocyclization reactions of the tethered phthalimides and naphthalimides and the length of the polyethylenoxy chain. Finally, the roles played by chain type and length in governing photoreaction efficiencies were investigated by using intramolecular competition in photoreactions of polyethylenoxy and polymethylene bis-tethered phthalimides. Mechanistic interpretations and synthetic consequences of the observations made in this study are discussed.

Observations Made in Exploring a Pyridinium Salt Photochemical Approach to the Synthesis of (+)-Lactacystin

The key step in a strategy for the synthesis of (+)-lactacystin involving photocyclization reaction of a cyclopenta-fused pyridinium salt has been probed by using a model substrate. Observations made in this effort led to the discovery of a highly unusual cascade process that leads to stereoselective formation of an interesting tricyclic carbamate. The results of this study are presented and discussed in the context of a (+)-lactacystin synthetic approach.

Photocyclization reaction of a diarylmaleimide derivative in polar solvents

Photochromism of a symmetric diarylmaleimide derivative, having two thiophene rings (1), and a non-symmetric derivative having a S,S-dioxide thiophene ring and a thiophene ring (2) as the aryl moieties, was studied in various solvents. The photocyclization quantum yield of gradually decreased with increasing the solvent polarity and the reaction was not observed in polar solvents, such as ethanol and acetonitrile; on the other hand, such a strong solvent dependence of the photocyclization reaction was not observed for ; the different behavior is attributed to the weaker electron donating ability of the S,S-dioxide thiophene ring.

β‐Silyl Arenes in the Arene—Olefin Photocyclization Reaction.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Preferential formation of cis-4,5-dihydrooxazole derivatives via photoinduced electron transfer-initiated cyclization of N-acyl-α-dehydroarylalanine alkyl esters

The alkyl, aryl, and acyl substituent effects on the photoinduced electron transfer-initiated cyclization reaction of the title compounds ( 1) were investigated in polar solvents from mechanistic and synthetic points of view. The irradiation of ( Z)- 1 in methanol containing triethylamine (TEA) was found to quantitatively give cis- and trans-4,5-dihydrooxazole derivatives ( cis- 2 and trans- 2). In addition to thermodynamic considerations for electron transfer and fluorescence quenching in the presence of TEA, acyl and aryl substituent effects on the emission intensity and photoreactivity of 1 confirmed the involvement of consecutive electron transfer reactions that form ( E)-arylmethylene radical anion and ( E)- N-acyl radical anion intermediates. It was also confirmed that the cyclization of the latter intermediate eventually leads to 2. On the basis of the finding that the selectivity for cis- 2 is greatly increased with increasing the steric bulkiness of alkyl and aryl substituents in 1, it was concluded that steric hindrance of these substituents toward hydrogen shift in the cyclized biradical intermediate, precursor of 2, is responsible for the kinetically controlled hydrogen shift in this intermediate. A product composition analysis showed that the protic polar solvent, methanol, of hydrogen-bonding solvation ability is a most suitable solvent for the photocyclization reactions examined.

Synthesis of Substituted 3,4‐Dihydroquinolin‐2(1H)‐one Derivatives by Sequential Ugi/Acrylanilide [6π]‐Photocyclizations.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.