NIR-Sensitized Activated Photoreaction between Cyanines and Oxime Esters: Free-Radical Photopolymerization

Cyanines comprising either a benzo[e]- or benzo[c,d]indolium core facilitate initiation of radical photopolymerization combined with high power NIR-LED prototypes emitting at 805 nm, 860 nm, or 870 nm, while different oxime esters function as radical coinitiators. Radical photopolymerization followed an initiation mechanism based on the participation of excited states, requiring additional thermal energy to overcome an existing intrinsic activation barrier. Heat released by nonradiative deactivation of the sensitizer favored the system, even under conditions where a thermally activated photoinduced electron transfer controls the reaction protocol. The heat generated internally by the NIR sensitizer promotes generation of the initiating reactive radicals. Sensitizers with a barbiturate group at the meso-position preferred to bleach directly, while sensitizers carrying a cyclopentene moiety unexpectedly initiated the photosensitized mechanism.     

Near‐Infrared Free‐Radical and Free‐Radical‐Promoted Cationic Photopolymerizations by In‐Source Lighting Using Upconverting Glass

A method is presented for the initiation of free‐radical and free‐radical‐promoted cationic photopolymerizations by in‐source lighting in the near‐infrared (NIR) region using upconverting glass (UCG). This approach utilizes laser irradiation of UCG at 975 nm in the presence of fluorescein (FL) and pentamethyldiethylene triamine (PMDETA). FL excited by light emitted from the UCG undergoes electron‐transfer reactions with PMDETA to form free radicals capable of initiating polymerization of methyl methacrylate. To execute the corresponding free‐radical‐promoted cationic polymerization of cyclohexene oxide, isobutyl vinyl ether, and N ‐vinyl carbazole, it was necessary to use FL, dimethyl aniline (DMA), and diphenyliodonium hexafluorophosphate as sensitizer, coinitiator, and oxidant, respectively. Iodonium ions promptly oxidize DMA radicals formed to the corresponding cations. Thus, cationic polymerization with efficiency comparable to the conventional irradiation source was achieved.     

A Supramolecular Radical Dimer: High‐Efficiency NIR‐II Photothermal Conversion and Therapy

Photothermal therapy at the NIR‐II biowindow (1000–1350 nm) is drawing increasing interest because of its large penetration depth and maximum permissible exposure. Now, the supramolecular radical dimer, fabricated by N,N′‐dimethylated dipyridinium thiazolo[5,4‐d]thiazole radical cation (MPT^.+) and cucurbit[8]uril (CB[8]), achieves strong absorption at NIR‐II biowindow. The supramolecular radical dimer (2MPT^.+‐CB[8]) showed highly efficient photothermal conversion and improved stability, thus contributing to the strong inhibition on HegG2 cancer cell under 1064 nm irradiation even penetrating through chicken breast tissue. This work provides a novel approach to construct NIR‐II chromophore by tailor‐made assembly of organic radicals. It is anticipated that this study provides a new strategy to achieve NIR‐II photothermal therapy and holds promises in luminescence materials, optoelectronic materials, and also biosensing.     

Photosensitization mechanisms in photopolymer coating film containing photoinitiators sensitized by aminochalcone‐type dye for computer‐to‐photopolymer plate

Photosensitization mechanisms in photopolymer coating film containing an aminochalcone‐type dye sensitizer and a radical generating reagent, sensitizer dyes, (E)‐3‐(9‐julolidinyl)‐1‐phenyl‐2‐propen‐1‐one (A), (E)‐2‐(9‐julolidinyl)‐methylene‐1‐indanone (B), 9‐benzoyl‐2,3,6,7‐tetrahydro‐1H,5H‐benzo[i,j]‐furano‐[3,2‐g]quinolizine (C), 4‐(dimethylamino) chalcone (D) and a radical‐generating reagent, 2,4,6‐tris (trichloromethyl)‐1,3,5‐triazine (TCT), were investigated by laser flash photolysis using a total reflection cell. Weak fluorescence and strong broad triplet absorption were detected. The fluorescence was statically quenched by TCT at quenching distances (R_f) of 15, 14, 20 and 14 Å for A, B, C and D as well as the triplet initial absorption, at quenching distances (R_t) of 16, 16, 16 and 14 for A, B, C and D, similar to the fluorescence quenching distances. The triplet decay time of the dyes was inefficiently quenched by TCT with the rate constants (k _q) of 1.9, 3.1, 0.7 and 1.0×10⁵ mol⁻¹/dm³/s for A, B, C and D. The sensitivity of photopolymers containing a sensitizer dye and a TCT was obtained at an excitation of 488 nm corresponding to the emission peaks of argon ion laser of 1.1, 0.2, 0.54 and 9.1 mJ cm² for A, B, C and D. The results indicated that the static sensitization process from the fluorescent singlet excited state of the dyes to the ground state of TCT was predominant, and the high sensitivity for A and B was caused by the high absorbance at 488 nm and that for C by the high fluorescent quenching distance. Copyright © 1999 John Wiley & Sons, Ltd.     

Tuning the Spectroscopic,Electrochemical, and Photovoltaic Properties of Triaryl Amine Based Sensitizers through Ring‐Fused Thiophene Bridges

The ring‐fused thiophene derivatives benzo[c]thiophene and its precursor bicyclo[2.2.2]octadiene (BCOD) have been introduced as π‐conjugated spacers for organic push–pull sensitizers with dihexyloxy‐substituted triphenylamine as donor and cyanoacrylic acid as acceptor ( OL1 , OL2 , OL3 , OL4 , OL5 , OL6 ). The effects of the fused ring on the spectroscopic and electrochemical properties of these sensitizers and their photovoltaic performance in dye‐sensitized solar cells have been evaluated. Introduction of a binary benzo[c]thiophene and ethylenedioxy thiophene as π bridge caused a significant red shift of the characteristic intramolecular charge‐transfer band to 642 nm. It is found that the sensitizer OL3 , which contains one benzo[c]thiophene unit as π linker, gives the highest overall conversion efficiency of 5.03 % among all these dyes.     

The Thermal Rearrangement of an NHC‐Ligated 3‐Benzoborepin to an NHC‐Boranorcaradiene

An N‐heterocyclic‐carbene‐ligated 3‐benzoborepin with a bridged structure has been synthesized by double radical trans‐hydroboration of benzo[3,4]cycloundec‐3‐ene‐1,5‐diyne with an N‐heterocyclic carbene borane. The thermal reaction of the NHC‐ligated borepin at 150 °C gives an isolable NHC‐boranorcaradiene. Experiments and density functional theory calculations support a mechanism whereby the borepin initially rearranges to a boranorcaradiene by a thermal 6π‐electrocyclic reaction. This is followed by 1,5‐boron shift to give a rearranged boranorcaradiene. This shift occurs with stereoinversion at boron through a transition state with open‐shell diradical character. This is the first example of the isolation of a boranorcaradiene from a thermal reaction of a borepin.     

Keto‐benzo[h]‐Coumarin‐Based Near‐Infrared Dyes with Large Stokes Shifts for Bioimaging Applications

Fluorescence imaging is a promising tool for the visualization of biomolecules in living systems and there is great demand for new fluorescent dyes that absorb and emit in the near‐infrared (NIR) region. Herein, we constructed three new fluorescent dyes ( NBC dyes) based on keto‐benzo[h]coumarin ( k‐BC ) and benzopyrilium salts. These dyes showed large Stokes shifts (>100 nm) and NIR emission (>800 nm). The relationship between the structures and optical properties of these dyes was further investigated by using density functional theory calculations at the B3LYP/6‐3G level of theory. Fluorescence images indicated that the fabricated dyes exhibited good photostability and low cytotoxicity and, thus, have potential applications as imaging agents in living cells and animals.     

Near‐IR Emitting Iridium(III) Complexes with Heteroaromatic β‐Diketonate Ancillary Ligands for Efficient Solution‐Processed OLEDs: Structure–Property Correlations

Three NIR‐emitting neutral Ir^III complexes [Ir(iqbt)₂(dpm)] ( 1 ), [Ir(iqbt)₂(tta)] ( 2 ), and [Ir(iqbt)₂(dtdk)] ( 3 ) based on the 1‐(benzo[b]thiophen‐2‐yl)‐isoquinolinate (iqtb) were synthesized and characterized (dpm=2,2,6,6‐tetramethyl‐3,5‐heptanedionate; tta=2‐thienoyltrifluoroacetonate; dtdk=1,3‐di(thiophen‐2‐yl)propane‐1,3‐dionate). The compounds emit between λ=680 and 850 nm with high luminescence quantum yields (up to 16 %). By combining electrochemistry, photophysical measurements, and computational modelling, the relationship between the structure, energy levels, and properties were investigated. NIR‐emitting, solution‐processed phosphorescent organic light‐emitting devices (PHOLEDs) were fabricated using the complexes. The devices show remarkable external quantum efficiencies (above 3 % with 1 ) with negligible efficiency roll‐off values, exceeding the highest reported values for solution‐processible NIR emitters.     

Efficient photopolymerization of thick pigmented systems using upconversion nanoparticles‐assisted photochemistry

Photopolymerization of thick pigmented systems still remains challenging due to the light screening effect of the pigments. Here, we present a facile method based on upconversion nanoparticles (UCNPs)‐assisted photochemistry to achieve efficient photopolymerization and improved curing depth of pigmented systems. Under a 980‐nm laser irradiation, UCNPs are able to convert NIR light into UV and visible light to activate photoinitiators for the initiation of polymerization. Influencing factors on photopolymerization were systematically investigated. With optimal parameters, 25.5 mm of photopolymerization depth combined with 70% of maximal double bond conversion was obtained. The peak temperature of 120.4 °C during UCNPs‐assisted photopolymerization is comparable with or lower than that of some reported frontal photopolymerization applied to prepare functional composite polymeric materials. Both indentation hardness and reduced modulus of the photocured materials using UCNPs as internal lamps were higher than those of the reference cured under traditional blue LED light. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 994–1002     

Cationic photopolymerization with the aid of pyridinium‐type salts

Pyridinium‐type salts containing an N‐ethoxy group belong to the family of onium salts and are photoinitiators appropriate for the polymerization of monomers such as oxiranes and vinyl ethers which are not polymerizable by a free radical mechanism. The initiation is accomplished by direct or indirect (sensitized) photolysis of the onium ion, with the former being restricted to the wavelength range of self absorption, the latter being applicable at wavelengths of visible light. An additionally useful tool, namely free radical‐mediated generation of initiating species enlarges the versatility of pyridinium salts as photoinitiators. In this connection, the oxidation of free radicals by pyridinium‐type ions and the free radical‐induced fragmentation of alkoxy pyridinium ions are addressed in this article. Moreover, an interesting application is noted concerning the synthesis of novel block copolymers with the aid of the onium salt‐based photopolymerization technique.     

Supramolecular Assemblies with Near‐Infrared Emission Mediated in Two Stages by Cucurbituril and Amphiphilic Calixarene for Lysosome‐Targeted Cell Imaging

A two‐stage mediated near‐infrared (NIR) emissive supramolecular assembly for lysosome‐targeted cell imaging is presented. 4,4′‐Anthracene‐9,10‐diylbis(ethene‐2,1‐diyl))bis(1‐ethylpyridin‐1‐ium) bromide (ENDT) was synthesized as an organic dye with weak fluorescence emission at 625 nm. When ENDT complexes with cucurbit[8]uril (CB[8]), this binary supramolecular complex assembles into nanorods with a near‐infrared fluorescence emission (655 nm) and fluorescence enhancement as the first stage. Such supramolecular complexes interact with lower‐rim dodecyl‐modified sulfonatocalix[4]arene (SC4AD) to form nanoparticles for further fluorescence enhancement as the second stage. Furthermore, based on a co‐staining experiment with LysoTracker Blue, such nanoparticles can be applied in NIR lysosome‐targeted cell imaging.     

Acrylate nanolatex via self‐initiated photopolymerization

The use of UV light to initiate emulsion polymerization processes is generally overlooked, whilst extensive literature exists on photocuring of monomer films. In this study, the unique potential of UV light to produce at ambient temperature polyacrylate latexes without initiator was exploited. Although radical initiators are utilized at low concentration, their cost, toxicity, and odor provide incentives for finding alternatives. Starting with concentrated (30 wt %) and low scattering acrylate miniemulsions (droplet diameter <100 nm), it was demonstrated that acrylate self‐initiation can promote an efficient and fast photopolymerization in micrometer‐scale reactor (spectrophotometric cell) and lab‐scale photoreactor. Herein, all kinetic, colloidal, and mechanistic aspects involved in the self‐initiation of acrylate miniemulsion were extensively examined to provide a complete picture. In particular, the effects of droplet size, initiating wavelength, optical path, and irradiance on the course of the polymerization were thoroughly discussed. A diradical self‐initiation pathway is the most likely mechanism. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1843–1853     

A Main‐Chain Liquid‐Crystalline Oligomer Prepared by in situ Photopolymerization of an LC Monomer Having Cinnamate Moieties

Summary: A liquid‐crystalline (LC) compound, having a cinnamate moiety on each end of the molecule, was synthesized and irradiated with UV light in its LC phase in the presence of a triplet sensitizer. Various measurements of the irradiated sample revealed that the linearly structured LC oligomers were formed by [2+2] cycloaddition of the cinnamate moieties, and that the resultant cyclobutane units dominantly assumed an anti head‐to‐head configuration.

Schematic structures of the LC oligomer obtained by photopolymerization.     

Syntheses of Some 3—[1′（1′H）—Substituent—pyrazol—5′—yl] benzo [5,6] coumarins

3-[1′(1′H)-Substituent-pyrazol-5′-yl]benzo[5,6]coumarins and 3-(1′,2′-oxazol-5′-yl)benzo[5,6]coumarin were prepared via condensation of 3-(2′-formyl-1′-chlorovinyl)benzo[5,6] coumarin with hydrazine derivatives or hydroxylamine.Reaction of 3-[1′(1′H)-pyrazol-5′-yl]benzo[5,6]coumarin with alkyl halides,olefinic compunds or acid chlorides are described.     

3-氨基-9-乙基咔唑敏化丙烯腈的光聚合

研究了３ － 氨基－ ９－ 乙基咔唑光引发丙烯腈光聚合的动力学关系,并初步讨论了其引发机理。     

New High‐Power LEDs Open Photochemistry for Near‐Infrared‐Sensitized Radical and Cationic Photopolymerization

Cyanines derived from heptamethines were investigated in combination with iodonium salts as initiators of the radical polymerization of tripropylene glycol diacrylate and epoxides derived from bisphenol‐A‐diglycidylether. A new near‐infrared (NIR) LED prototype emitting at 805 nm with an exposure intensity of 1.2 W cm^?2 facilitated initiation of both radical and cationic polymerization using sensitizers derived from cyanines. This new light‐emitting device has brought new insight into the photochemistry of cyanines with the general structure 1 because a combination of photonic and thermal processes strongly influences reaction pathways. In particular, cationic cyanines comprising a cyclopentene moiety and diphenylamino group in the center initiated the cationic polymerization of epoxides. Selective oxidation of this unit explains why specifically these derivatives may function as initiators for cationic polymerization. In contrast, when the diphenylamino group was replaced by a barbital group at the meso‐position cationic polymerization of epoxides was not initiated.     

Synthesis of benzo[b]thieno‐ and benzo[b]furano‐[2,3‐a]pyrrolo[3,4‐c]carbazole‐5‐, ‐7‐ and ‐5,7‐dione

Benzo[b]thieno[2,3‐a]pyrrolo[3,4‐c]carbazoles and benzo[b]furano[2,3‐a]pyrrolo[3,4‐c]carbazoles were prepared from 2‐(2‐benzo[b]thieno)‐ (8) and 2‐(2‐benzo[b]furano)‐3‐[3‐(2,5‐dioxo‐lH‐pyrrolidinyl)]indole (9) by a palladium(II)acetate/tetrachloro‐1,4‐benzoquinone oxidative A‐E ring closure.     

Heteroarene‐fused π‐conjugated main‐chain polymers containing 4,7‐bis(4‐octylthiophen‐2‐yl)benzo[c][1,2,5]thiadiazole or 2,5‐bis(4‐octylthiophen‐2‐yl)thiazolo[5,4‐d]thiazole and their application to photovoltaic devices

Two conjugated main‐chain polymers consisting of heteroarene‐fused π‐conjuagted donor moiety alternating with 4,7‐bis(5‐bromo‐4‐octylthiophen‐2‐yl)benzo[c][1,2,5]thiadiazole (P1) or 2,5‐bis(5‐bromo‐4‐octylthiophen‐2‐yl) thiazolo[5,4‐d]thiazole (P2) units have been synthesized. They are intrinsically amorphous in nature and do not exhibit crystalline melting temperatures during thermal analysis. The effect of the fused rings on the thermal, optical, electrochemical, charge transport, and photovoltaic properties of these polymers has been investigated. The polymer (P1) containing 4,7‐bis(5‐bromo‐4‐octylthiophen‐2‐yl)benzo[c][1,2,5] thiadiazole has a broad absorption extending from 300 to 600 nm with optical bandgaps as low as 2.02 eV. The HOMO levels (5.42 to 5.29 eV) are more sensitive to the choice of acceptor. The polymers were employed to fabricate organic photovoltaic cells with methanofullerene [6,6]‐phenyl C71‐butyric acid methyl ester (PC₇₁BM). As a result, the polymer solar cell device containing P1 had the best preliminary results with an open‐circuit voltage of 0.61 V, a short‐circuit current density of 6.19 mA/cm², and a fill factor of 0.32, offering an overall power conversion efficiency of 1.21%. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Investigations of a novel process to the framework of benzo[c]cinnoline

A novel synthetic process leading to the framework of benzo[c]cinnoline has been discovered and investigated. The process is composed of two separate reactions, the first of which is a partial reduction of the nitro groups of the 2,2'-dinitrobiphenyl, a process that we believe proceeds via a SET mechanism to yield the hydroxyamino and nitroso groups. In the following step the cyclization takes place under formation of the -N=N- bond. We believe that this process take place via a radical mechanism through the nitroso radical anion. The novel process affords either benzo[c]cinnoline or benzo[c]cinnoline N-oxide, both in high yields, 93% and 91%, respectively. To obtain benzo[c]cinnoline, the reaction is conducted with an alcohol as solvent and an alkoxide as the base, while for benzo[c]cinnoline N-oxide, water is used as solvent with sodium hydroxide as the base. To establish the latter procedure, statistical experimental design and multivariate modeling were utilized to reveal the response surface for the reaction and to determine the optimal conditions for the reaction. A proposal for the complex reaction mechanism is given. During the corroboration of the mechanism, a new deoxygenation reaction for converting benzo[c]cinnoline N-oxide into benzo[c]cinnoline was discovered. The reaction is conducted by treating the N-oxide with sodium ethoxide at elevated temperature to achieve near-quantitative conversion into benzo[c]cinnoline in a yield of 96%.     

Synthesis of Novel 7‐methylene‐6,7‐dihyrobenzo[f]Benzo[4,5]Imidazo[1,2‐d][1,4]Oxazepines via Base‐mediated Regioselective Intramolecular Hydroamination

A versatile and transition metal‐free approach for the synthesis of new 7‐methylene‐6,7‐dihyrobenzo[f]benzo[4,5]imidazo[1,2‐d][1,4]oxazepines were developed by an efficient 7‐exo‐dig regioselective hydroamination of 2‐(2‐(prop‐2‐yn‐1‐yloxy)phenyl)‐1H‐benzo[d]imidazole in the presence of potassium carbonate in DMF at 90°C.