Photocyclization Reaction Research Articles

An Evaluation of Optical Absorbance Kinetics for the Detection of Micro-Porosity in Molecularly Doped Polymer Thin-Films

The use of optical absorbance kinetics to identify micro-porous regions in doped polymer films is evaluated. Data are presented for a series of hydrazone doped polymer films which are found to optically bleach upon exposure to an ultra violet (UV) radiation source. The UV absorbance kinetics are found to exhibit distinctive characteristics for the various polymers studied, with changes in film absorbance occurring either in a fast (<103 s) or slow (>104 s) timescale. An interpretation of these distinctive timescales based upon a cellular-automata model of the absorbance kinetics suggests that the underlying photo-oxidation of the hydrazone is highly sensitive to underlying micro-porosity in the films which controls the necessary supply of absorbed oxygen for photo-cyclic reaction.

Visible-light-driven photocyclization reaction: photocatalyst-free mediated intramolecular N–N coupling for the synthesis of 2H-indazole-3-carboxamides from aryl azides

A visible-light-driven photocyclization reaction of aryl azides to access 2H-indazole-3-carboxamides in moderate to excellent yields has been realized efficiently under photocatalyst-free and external additive-free conditions.

Synthesis of azahelicenes through Mallory reaction of imine precursors: corannulene substrates provide an exception to the rule in oxidative photocyclizations of diarylethenes.

Typically, the synthesis of phenanthrene-based polycyclic aromatic hydrocarbons relies on the Mallory reaction. In this approach, stilbene (PhCH Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CHPh)-based precursors undergo an oxidative photocyclization reaction to join the two adjacent aromatic rings into an extended aromatic structure. However, if one CC carbon atom is replaced by a nitrogen atom (CN), the synthesis becomes practically infeasible. Here, we show the very first examples of a successful Mallory reaction on stilbene-like imine precursors involving the molecularly curved corannulene nucleus. The isolated yields exceed 90% and the resulting single and double aza[4]helicenes exhibit adjustable high affinity for electrons.

Conformational Control of the Photodynamics of a Bilirubin Dipyrrinone Subunit: Femtosecond Spectroscopy Combined with Nonadiabatic Simulations.

The photochemistry of bilirubin has been extensively studied due to its importance in the phototherapy of hyperbilirubinemia. In the present work, we investigated the ultrafast photodynamics of a bilirubin dipyrrinone subunit, vinylneoxanthobilirubic acid methyl ester. The photoisomerization and photocyclization reactions of its (E) and (Z) isomers were studied using femtosecond transient absorption spectroscopy and by multireference electronic structure theory, where the nonadiabatic dynamics was modeled with a Landau-Zener surface hopping technique. The following picture has emerged from the combined theoretical and experimental approach. Upon excitation, dipyrrinone undergoes a very fast vibrational relaxation, followed by an internal conversion on a picosecond time scale. The internal conversion leads either to photoisomerization or regeneration of the starting material. Further relaxation dynamics on the order of tens of picoseconds was observed in the ground state. The nonadiabatic simulations revealed a strong conformational control of the photodynamics. The ultrafast formation of a cyclic photochemical product from a less-populated conformer of the studied subunit was predicted by our calculations. We discuss the relevance of the present finding for the photochemistry of native bilirubin. The work has also pointed to the limits of semiclassical nonadiabatic simulations for simulating longer photochemical processes, probably due to the zero-point leakage issue.

Novel bisbenzopyronopyran derivatives: photochemical synthesis and their in‐vitro antimicrobial studies

AbstractThe present research work describes the productive synthesis of novel bisbenzopyronopyran derivatives 4(a‐h) and 5(a‐h) via the photocyclization reactions of bischromones 3(a‐h) under the inert conditions. The latter compounds have been realized efficiently through the O‐alkylation reactions of the 3‐hydroxychromone 2 with suitable dihalogenated aliphatic/aromatic/heteroaromatic reagents in the presence of dry acetone/anhydrous K2CO3/Bu4N+I− (PTC). The cyclization reaction of chalcone 1 under the Algar‐Flynn‐Oyamada reaction conditions (KOH/H2O2) could results in the formation of compound 2 in the good yield. The structural scaffolds of the newly prepared bischromones and resultant bisbenzopyronopyrans have been certified from the meticulous analysis of their various spectroscopic parameters such as UV‐Vis, IR, 1H/13C‐NMR, and ESI‐MS. It was found that o/m/p‐xylene and pyridine‐linked final symmetrical bistetracycles exhibited higher antimicrobial potencies as compared to alkyl chain‐linked cyclized products. The bischromones 3(a‐h) could be able to endow modest level of antimicrobial behavior.

Theoretical study on the photocyclization reactivity mechanism in a diarylethene derivative with multicolour fluorescence modulation

For a photochromic spiro-diarylethene derivative (Spiro-DAE), its photocyclization reaction and multicolour fluorescence modulation performances were investigated based on a series of density functionals calculations in this work. Some elementary properties such as geometric and electronic structures at ground and the first excited state (S1), absorption and emission spectra in respective open-ring and closed-ring structures were compared, which indicate the cyclization reaction may occur at S1. It is further verified by the lower activation barrier (3.4 kcal/mol) of the transition state at S1 potential energy surface. The photochromic reaction rates for both cyclization and cycloreversion processes were quantitatively estimated, which suggests the much smaller radiative and internal conversion rates contribute to the higher photocyclization rate and thus efficiency. Furthermore, we suspect that the dihydroacridine fragment may make important contribution to the cyclization reaction occurring at S1 considering its contribution to electronic structure.

Natural and Synthetic Spirobutenolides and Spirobutyrolactones

AbstractSpirobutenolides and spirobutyrolactones structural motifs are widespread in various natural products that exhibit a broad array of biological activities. Additionally, their synthetic analogues also serve as biologically active compounds and building blocks of complex molecules. Owing to the wide range of pharmacological activities and structural diversity of the spirobutenolides and spirobutyrolactones, various efficient synthetic methodologies have been established to construct such interesting scaffolds. In the past decades, numerous total syntheses of spirobutenolides and spirobutyrolactones containing natural products have been reported. Structurally diverse spirobutenolides and spirobutyrolactones have been synthesized by using singlet oxygen, Mannich reaction, aldol condensation, rearrangement reaction, Reformatsky reaction, Michael‐addition cyclization, Diels‐Alder reaction, photocyclization reaction, and pericyclic reactions. Recently, metal‐catalyzed cyclization, photocatalyzed radical cyclization, Baylis‐Hillman reaction, asymmetric organocatalysis, NHC catalysis, ring contraction reactions, and hypervalent iodine catalysis have emerged as powerful tools to architect these nuclei. This review gives an overview of advancements in chemically and biologically relevant spirobutenolides and spirobutyrolactones of natural and synthetic origin. It also covers the newer methodologies for the construction of natural as well as synthetic spirobutenolides and spirobutyrolactones along with their potential applications.

Synthesis of novel benzocoronene tetracarboxdiimides for fluorescent imaging of latent fingerprints

Benzocoronene tetracarboxdiimide (CDI 1a) is prepared by ring annulation of perylene diimide via Suzuki coupling and sunlight-driven photocyclization reactions. Oxidative photocyclization predominantly occurred at the carbon position ortho to the CHO group. It is demonstrated to undergo aggregation in 30 % DMF: H2O with degree of aggregation and Franck-Condon factor value reaches 0.94 and 0.64, respectively. The emission spectrum of CDI 1a shows monomer band at 568 nm in DMF and aggregation band at 688 nm in 30 % DMF: H2O with onset of emission color from yellow to reddish-pink. These near-IR fluorescent aggregates are proved to be an ideal fluorescent material for imaging LFPs using solution and powder-dusting methods. The papillary ridges detail (1st and 2nd level of information) on various non-porous surfaces (aluminum, steel, compact disc, glass etc.) and porous surfaces (paper, floor tiles) are presented by CDI 1a.

Photoswitchable Photon Upconversion from Turn-on Mode Fluorescent Diarylethenes

Photon upconversion (UC) is one kind of anti-Stokes shift process, which generally requires a combination of two or more low-energy photons to produce one high-energy photon. However, another inter...

Unexpected molecular diversity of vertebrate nonvisual opsin Opn5.

Animals depend on light from their external environment to provide information for physiological functions such as vision, photoentrainment of circadian and circannual rhythms, photoperiodism, and background adaptation. Animals have a variety of photoreceptor cells that perform these functions, not only in the retina but also in other tissues, including brain tissue. In these cells, opsins function as universal photoreceptive proteins responsible for both visual and nonvisual photoreception. All opsins identified thus far bind either 11-cis or all-trans retinal as a chromophore and are classified into several groups based on their amino acid sequences. Opn5 forms an independent group that has diversified among vertebrate species. Most mammals only have one Opn5 gene, Opn5m, while nonmammalian vertebrates have two additional Opn5 subtypes, Opn5L1 and Opn5L2. Among these subtypes, Opn5m and Opn5L2 are UV-sensitive pigments in the dark. UV irradiation converts them into the visible light-sensitive active state, which converts back to the dark state by visible light irradiation. Opn5m and Opn5L2 therefore behave as bistable pigments. By contrast, Opn5L1 exclusively binds all-trans retinal to form the active state in the dark. Opn5L1 is converted to the resting state by light irradiation and subsequently reverts to the active state by a thermal process. Thus, Opn5L1 is categorized as a unique reverse photoreceptor whose activity is regulated by its photocyclic reaction. In this review, I introduce the diversity of molecular properties that have been described for vertebrate Opn5 subtypes and their physiological relevance.

Studies on the photocyclization reaction of 8‐styryl‐substituted coralyne derivatives

AbstractThe photoreactivity of four 8‐styryl‐substituted coralyne derivatives was examined by UV/VIS‐ and 1H‐NMR‐spectroscopy. Except for the dimethylamino‐substituted derivative, these cationic azoniaheterocyclic dyes undergo photocyclization that most likely proceeds through an initial E‐Z‐isomerization of the double bond. Subsequent oxidation of the intermediates under aerobic conditions gave the pyrrolo‐annelated quinolizinium derivatives as final products, thus providing a useful synthetic route to polycyclic azoniahetarene derivatives. The 6‐(4‐chlorophenyl)‐substituted pyrroloquinolizinium derivative was isolated on a preparative scale, and the investigation of its photophysical properties revealed significantly red‐shifted absorption (λabs = 465–480 nm) and emission bands (λfl = 550–562 nm) in comparison to the parent coralyne and the styryl‐substituted derivatives.

Non-Oxido-Vanadium(IV) Metalloradical Complexes with Bidentate 1,2-Dithienylethene Ligands: Observation of Reversible Cyclization of the Ligand Scaffold in Solution.

Derivatives of 1,2‐dithienylethene (DTE) have superb photochromic properties due to an efficient reversible photocyclization reaction of their hexatriene structure and, thus, have application potential in materials for optoelectronics and (multi‐responsive) molecular switches. Transition‐metal complexes bearing switchable DTE motifs commonly incorporate their coordination site rather distant from the hexatriene system. In this work the redox active ligand 1,2‐bis(2,5‐dimethylthiophen‐3‐yl)ethane‐1,2‐dione is described, which reacts with [V(TMEDA)2Cl2] to give a rare non‐oxido vanadium(IV) species 3(M,M/P,P). This blue complex has two bidentate en‐diolato ligands which chelate the VIV center and give rise to two five‐membered metallacycles with the adjacent hexatriene DTE backbone bearing axial chirality. Upon irradiation with UVA light or prolonged heating in solution, the blue compound 3(M,M/P,P) converts into the purple atropisomer 4(para,M/para,P). Both complexes were isolated and structurally characterized by single‐crystal X‐ray diffraction analysis (using lab source and synchrotron radiation). The antiparallel configuration (M or P helicity) present in both 3(M,M/P,P) and 4(para,M/para,P) is a prerequisite for (reversible) 6π cyclization reactions. A CW EPR spectroscopic study reveals the metalloradical character for 3(M,M/P,P) and 4(para,M/para,P) and indicates dynamic reversible cyclization of the DTE backbone in complex 3(M,M/P,P) at ambient temperature in solution.

Photocycle Dynamics of the Archaerhodopsin 3 Based Fluorescent Voltage Sensor QuasAr1.

The retinal photocycle dynamics of the fluorescent voltage sensor QuasAr1 (Archaerhodopsin 3 P60S-T80S-D95H-D106H-F161V mutant from Halorubrum sodomense) in pH 8 Tris buffer was studied. The samples were photoexcited to the first absorption band of the protonated retinal Schiff base (PRSB) Ret_580 (absorption maximum at λmax ≈ 580 nm), and the retinal Schiff base photoisomerization and protonation state changes were followed by absorption spectra recordings during light exposure and after light exposure. Ret_580 turned out to be composed of two protonated retinal Schiff base isomers, namely Ret_580I and Ret_580II. Photoexcitation of Ret_580I resulted in barrier-involved isomerization to Ret_540 (quantum yield ≈ 0.056) and subsequent retinal proton release leading to Ret_410 deprotonated retinal Schiff base (RSB). In the dark, Ret_410 partially recovered to Ret_580I and partially stabilized to irreversible Ret_400 due to apoprotein restructuring (Ret_410 lifetime ≈ 2 h). Photoexcitation of Ret_580II resulted in barrier-involved isomerization to Ret_640 (quantum yield ≈ 0.00135) and subsequent deprotonation to Ret_370 (RSB). In the dark, Ret_370 partially recovered to Ret_580II and partially stabilized to irreversible Ret_350 due to apoprotein restructuring (Ret_370 lifetime ≈ 10 h). Photocycle schemes and reaction coordinate diagrams for Ret_580I and Ret_580II were developed and photocyle parameters were determined.

Mechanistic analysis on the photochemistry of the anti-inflammatory drug etoricoxib in aqueous solution. Cytotoxicity of photoproducts

Photophysical and photochemical properties of the non-steroidal anti-inflammatory drug Etoricoxib was analyzing in aqueous media at different pH values. The mechanistic and kinetic aspects of the photodegradation processes involved, induced by UV irradiation of the drug were also investigated, as well as the generation of reactive oxygen species and transient excited species by the anti-inflammatory. Moreover, due to the fact that the photoproducts can be either less or more toxic than the parent pharmaceutical, the possible cytotoxic effects of etoricoxib and its photoproducts were analyzed in vitro on the Vero cell line. Etoricoxib undergoes pH-dependent photoinduced degradation processes when irradiated with UV light at 233 nm and 285 nm. The greater the degree of protonation, the greater the rate and quantum yield of photodegradation. The use of a variety of stationary and time-resolved techniques allowed us to propose a photodegradation mechanism for the anti-inflammatory. The main pathway involves the generation of an excited singlet state by UV light absorption that allows the formation of two isomeric photoproducts resulting from the photocyclization reaction of the excited etoricoxib. Likewise, the triplet excited state of the drug was detected and the spectrum of this transient species and its quantum yield are reported here for the first time. The triplet state could react with molecular oxygen and generate the reactive specie OH that lead to the photodegradation of the drug. On the other hand, it was possible to demonstrate that the products of the photocyclization can generated O2(1Δg) and be susceptible to photooxidation mediated by this species. By last, the in vitro cytotoxic test on Vero cell line (Neutral Red and MTT assay) revealed that the photoproducts can alter the viability of the cell by affecting de mitochondrial respiration processes.

Highly luminescent ladder dimer based on perylene diimides and norbornane

Solution processable functional ladder-type materials with well-defined structures attract tremendous interest from the researchers due to their extraordinary stability and intriguing photoelectric properties, while the development of efficient and versatile synthetic routes still remains as an enormous challenge. Herein, we report a novel synthetic strategy towards a ladder-type PDI dimer by efficient photo-cyclization reaction of the single stranded precursor. The incorporation of the norbornane bridge endows the ladder dimer with planar PDI units, zigzag molecular conformation, and good solubility in various solvents. Besides superior thermal and photo-stability, LPD exhibits fluorescent quantum yields (QY) of 90.8% and 25.7% in solution and film, respectively. Both values are significantly higher than those of the single-stranded counterpart SPD (85.1% and 7.5%).

Phosphahelicenes with (Thio)Phosphinic Acid and Ester Functions by the Oxidative Photocyclisation Approach.

Phosphahelicenes with thiophosphinic acid and ester functions have been obtained by the oxidative photocyclisation of olefins bearing both a benzophenanthrene and a benzophosphole unit. When the method has been extended to olefins bearing a partially saturated benzophospholene unit, a divergent regioselectivity of the photocyclisation step has been observed, leading to new helicenes in which the phosphorus function is located on the external rim of the helical backbone. The observed regioselectivity correlates well with the free-valence numbers of the atoms involved in the photocyclisation reaction (DFT calculations).

All-Visible-Light-Activated Dithienylethenes Induced by Intramolecular Proton Transfer.

The fast light-responsive dithienylethenes (DTEs) are one of the most attractive photochromic families because of their excellent thermal irreversibility and fatigue resistance. However, the all-visible-light-activated DTE system still remains challenging because most of them require the harmful high-energy ultraviolet light to trigger their photocyclization reaction. Here, we have for the first time borrowed a specific intramolecular proton transfer (IPT) process and rationally designed a series of all-visible-light-driven DTEs. Incorporating the IPT-functional group to DTE unit gives rise to an extra absorption band with a distinct red shift, which enables the photocyclization of DTEs under stimuli of visible light at 450 nm, as well as ensuring the desirable photoswitching efficiency. The isomerization from OH form to NH form induced by IPT can decrease the energy gap for excitation and photocyclization, thereby affording the all-visible-light-triggered photochromic performance, which can not only work well in a polar solvent system but also show its effectiveness in polymeric gel systems. In this regard, we can provide a general and reliable platform to construct all-visible-light-driven DTEs with excellent reversible photoswitching and broad applicability, especially with avoiding the use of harmful ultraviolet light to induce their photocyclization.

Fast and Efficient Method to Obtain Tagitinin F by Photocyclization of Tagitinin C.

There is some evidence in the literature of the photocyclization reaction of Tagitinin C (1) to Tagitinin F (2). Compound 2 has high pharmacological potential, but it is not easy to obtain, while compound 1 is easily obtained from a widespread plant, Tithonia diversifolia. Among different reaction conditions monitored, one was found that allowed the cyclization of 1 into 2 in <15min in a photo-dependent reaction. Scaling-up the photocyclization of the pure compound 1 into 2 demonstrated 100% yield, and the isolation of 2 from a UV-irradiated extract was eight-fold higher than the quantity isolated from the non-UV-irradiated extract. We were also able to better understand the process of photoconversion and determine methods to isolate and quantify these compounds, which are known for their important antitumoral activities among other important pharmacological properties.

Dynamic Topochemical Reaction Tuned by Guest Molecules in the Nanospace of a Metal-Organic Framework.

Reaction in well-designed solids allows yielding products with high selectivity and unique compounds that cannot be obtained in solution. However, the precise tuning of the arrangement of reactants in solids for the versatile application of solid-phase reactions remains a challenging subject. Here, a [2 + 2] photocyclization reaction at different positions of the carbon-carbon bonds is described in which the spatial arrangement of 4-styrylpyridines (4-spy) is changed by guest molecules in a flexible metal-organic framework. The 4-spy molecules undergo photodimerization between two carbon-carbon double bonds in the guest-free framework, whereas a reaction between olefinic and aromatic carbon-carbon bonds or the absence of reaction takes place in the solvent-incorporated form. This reactivity, which can be termed as "dynamic topochemistry" contributes to enforce the applicability of solid-phase reactions in synthetic chemistry.

Photochromic Performance of 5-Heteroaryl-4-vinyl-2-phenylthiazole Derivatives

Abstract Compounds 5-(5-methyl-2-phenyl-4-thiazolyl)-4-(5-methyl-1-phenyl-1-propenyl)-2-phenylthiazole 1a and 5-(2-methyl-5-phenyl-3-thienyl)-4-(2-methyl-1-phenyl-1-propenyl)-2-phenylthiazole 2a having an S-N heteroatom-contact interaction and a CH-N hydrogen bonding were synthesized in an attempt to obtain new photochromic compounds having terarylene and 1-aryl-2-vinylcyclopentene backbones. The S-N interaction and CH-N hydrogen bonding of 1a and 2a can be explained by DFT calculation and temperature dependent 1H NMR spectra. The tethering interactions are expected to stabilize the reactive conformation of 1a and 2a, and to increase the photocyclization quantum yield. Two 5-heteroaryl-4-vinyl-2-phenylthiazoles 1 and 2 underwent reversible photocyclization reactions from the open-ring isomers 1a and 2a to the closed-ring isomers 1b and 2b, respectively. The photocyclization quantum yields of 1a and 2a are 0.57 and 0.63, which are 3 times larger than that of 1-thiazolyl-2-vinylcyclopentene derivatives (0.20). The number of photochromic cycles exhibited by 1b was 50 in the presence of air, which is higher than that of 2b.