Poly(arylene ether)s from new biphenols containing imidoarylene and dicyanoarylene moieties

Novel poly(arylene ether)s were synthesized from new biphenol monomers 14–16 1 containing imido‐ or dicyanoarylene groups. The syntheses of these polymers were carried out in tetramethylene sulfone in the presence of anhydrous K₂CO_3, by a nucleophilic substitution condensation between the biphenol and activated difluoro compounds to give high molecular weight polymers. All the polymers have high T_g 's and good thermal stability as determined from DSC and TGA analysis. Inherent viscosities of these polymers are in the range of 0.33–0.63 dL/g. They are amorphous and readily soluble in NMP, DMF, and DMSO. The glass‐transition temperatures of the polymers range from 248–295 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1318–1322, 2000     

Synthesis and properties of novel poly(arylene ether)s and poly(arylene thioether)s based on a pyridazine biphenol or a phthalazine biphenol

Novel sulfur‐containing biphenol monomers were prepared in high yields by the reaction of 4‐mercaptophenol with chloropyridazine or chlorophthalazine compounds. High‐molecular‐weight poly(arylene ether)s were synthesized by a nucleophilic substitution reaction between these sulfur‐containing monomers and activated difluoro aromatic compounds. The inherent viscosities of these polymers ranged from 0.34 to 0.93 dL/g. The poly(pyridazine)s exhibited glass‐transition temperatures greater than 165 °C. The poly(phthalazine)s showed higher glass‐transition temperatures than the poly(pyridazine)s. A polymer synthesized from a bisphthalazinebiphenol and bis(4‐fluorophenyl)sulfone had the highest glass‐transition temperature (240 °C). The thermal stabilities of the poly(pyridazine)s and poly(phthalazine)s showed similar patterns of decomposition, with no significant weight loss below 390 °C. The poly(phthalazine)s were soluble in chlorinated solvents such as chloroform, and the poly(pyridazine)s were soluble in dipolar aprotic solvents such as N,N′‐dimethylacetamide. The soluble poly(pyridazine)s and poly(phthalazine)s could be cast into flexible films from solution. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 262–268, 2007     

Linear and Hyperbranched Poly(arylene ether)s from a New Semifluorinated AB Monomer

A new trifluoromethyl-activated AB monomer has been successfully synthesized by Pd-initiated coupling of 4-bromo anisole with 4-fluoro-3-trifluoromethylphenylboronic acid followed by demethylation. The monomer leads to a semifluorinated poly(arylene ether) by nucleophilic displacement polymerization reaction. The AB monomer has been further copolymerized with a corresponding AB ₂ monomer to form the corresponding semifluorinated hyperbranched (hb) poly(arylene ether). The resulting linear and hb poly(arylene ether)s exhibited weight average molecular weight of 75700 and 144100 g/mol, respectively. The hb copolymer exhibited better solubility in different organic solvents compared to the linear poly(arylene ether). The polymers showed excellent thermal stability up to 522°C at 10% wt loss in air and glass transition temperatures as high as 187°C. The mechanical properties of the linear poly(arylene ether) film 1a exhibited tensile strength at break of 89 MPa, elongation at break of up to 3% and a Young’s modulus value of 2.66 GPa. The films of the polymers were hydrophobic in nature and showed water contact angle as high as 93.6°.     

Eco-friendly fast synthesis and thermal degradation of optically active polyamides under microwave accelerating conditions

<正>An optically active bulky aromatic diacid chiral monomer,(2S)-4-[(4-methyl-2-phthalimidylpentanoyl-amino) benzoylamino]isophthalic acid(1),containing a rigid phthalimide and flexible L-leucine pendent group was synthesized in five steps.A fast and clean method for direct polyamidation reaction of monomer 1 with various aromatic diamines under microwave irradiation and conventional heating was performed.The polymerization reactions provided optically active polyamides with high yields and inherent viscosities in the range of 0.36-0.74 dL/g.Their thermal properties were evaluated by thermogravimetric analysis(TGA) and differential scanning calorimetry.TGA thermograms show that the polymers are thermally stable,10%weight loss temperatures are in excess of 385℃,and char yields at 800℃are higher than 56%.The data obtained from TGA were used to study the kinetics of thermal decomposition of the resulting polymers. The interpretation of kinetic parameters(E,ΔH,ΔS andΔG) of thermal decomposition stages was evaluated using Coats and Redfern equation.     

Cationic polymerization of isobutylene coinitiated by AlCl3 in the presence of ethyl benzoate

<正>The cationic polymerizations of isobutylene(IB) coinitiated by AlCl_3 were carried out in solvent mixture of n-hexane /methylene dichloride(n-hex/CH_2Cl_2) of 60/40 V/V in the presence of ethyl benzoate(EB) at various temperatures range from-80℃to-30℃.The effects of EB concentration([EB]) and polymerization temperature on monomer conversion,weight-average molecular weight(M_w) and molecular weight distribution(MWD,M_w/M_n) of polyisobutylene (PIB) products were investigated.The rate of polymerization decreased while M_w of PIB products increased with increasing [EB].The polymers with high molecular weight could be prepared in the presence of a suitable amount of EB.Significantly, the polymers with high M_w of 80.2×10~4 and 65.4×10~4 could be produced at-80℃and-70℃at[EB]=0.24×10~(-3) mol/L respectively,which were much higher than that(M_w=57.9×10~4) of PIB prepared at-100℃in the absence of EB.A simple but effective method for preparing the high molecular weight polyisobutylenes was developed in this work.It has been also found that the activation energy for propagation(E_p) depended on the polymerization temperature range in the presence of EB.An obvious inflection of the linear plots of lnX_n versus 1/T_p occurred at the temperature range from-60℃to-50℃at four different concentrations of EB from 0.19×10~(-3) mol/L to 0.33×10~(-3) mol/L,and thus the inflection temperature(T_(inf)) was in the range of-60℃to-50℃.When[EB]was in the range of 0.24×10~(-3) mol/L to 0.33×10~(-3) mol/L,E_p was determined to be around-12 kJ/mol when the polymerization was carried out at temperatures from-80℃to T_(inf) and to be around-28 kJ/mol at temperatures from T_(inf) to-15℃respectively.     

Polycarbazoles via C?N coupling reactions of phthaloyl bis‐9H‐carbazoles with activated difluorides

1,3‐Phthaloyl bis‐9H‐carbazole (MPC) and 1,4‐phthaloyl bis‐9H‐carbazole (PPC) were synthesized by a Friedel‐Crafts reaction of carbazole with terephthaloyl chloride or isophthaloyl chloride. Homopolymers were obtained by a C? N coupling reaction with activated difluorides and copolymers were synthesized with 4,4′‐biphenol as a comonomer by a nucleophilic substitution reaction between these NH‐ and OH‐containing monomers and the activated difluoro monomers. The inherent viscosities of the polymers ranged from 0.35 to 1.03 dL/g. These polymers exhibited glass‐transition temperatures greater than 238 °C with the PPC‐containing homopolymer showing the highest value, 326.4 °C. The thermal stabilities indicated no significant weight loss below 450 °C and the temperatures of 5% weight loss ranged from 514.0 to 546.3 °C. The polymers showed reasonable solubility in organic solvents such as DMAC, DMSO, and NMP. UV absorption and fluorescence emission properties are presented. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4326–4331, 2009     

Thianthrene as an activating group for the synthesis of poly(aryl ether thianthrene)s by nucleophilic aromatic substitution

A method for the preparation of poly(aryl ether thianthrene)s has been developed in which the aryl ether linkage is generated in the polymer‐forming reaction. The thianthrene heterocycle is sufficiently electron‐withdrawing to allow fluoro displacement with phenoxides by nucleophilic aromatic substitution. The monomer for this reaction, 2,7‐difluorothianthrene, can be synthesized in a moderate yield by a simple reaction sequence. Semiempirical calculations at the PM3 level suggest that 2,7‐difluorothianthrene is sufficiently activated, whereas NMR spectroscopy (¹H and ¹³C) indicates that the monomer is only slightly activated or (¹⁹F) not sufficiently activated for nucleophilic aromatic substitution. Model reactions with p‐cresol have demonstrated that the fluorine atoms on 2,7‐difluorothianthrene are readily displaced by phenoxides in high yields, and the process has been deemed suitable for polymer‐forming reactions. High‐molecular‐weight polymers have been produced from bisphenol A, bisphenol AF, and 4,4′‐biphenol. The polymers have been characterized with gel permeation chromatography, NMR spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry. The glass‐transition temperatures for the polymers of different compositions and molecular weights range from 138 to 181 °C, and all the polymers have shown high thermooxidative stability, with 5% weight loss values in an air environment approaching 500 °C. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6353–6363, 2004     

Synthesis and characterization of phthalazinone containing poly(arylene ether)s via a novel N–C coupling reaction

High‐molecular‐weight poly(phthalazinone)s with very high glass‐transition temperatures (T_g's) were synthesized via a novel N–C coupling reaction. New bisphthalazinone monomers ( 7a–e ) were synthesized from 2‐(4‐chlorobenzoyl) phthalic acid in two steps. Poly(phthalazinone)s, having inherent viscosities in the range of 0.34–0.91 dL/g, were prepared by the reaction of the bis(phthalazinone) monomers with an activated aryl halide in a dipolar aprotic solvent in the presence of potassium carbonate. The poly(phthalazinone)s exhibited T_g's greater than 230 °C. polymer 8b synthesized from diphenyl biphenol and bis(4‐flurophenyl) sulfone demonstrated the highest T_g of 297 °C. Thermal stabilities of the poly(phthalazinone)s were determined by thermogravimetric analysis. All the poly(phthalazinone)s showed a similar pattern of decomposition with no weight loss below 450 °C in nitrogen. The temperatures of 5% weight loss were observed to be about 500 °C. The poly(phthalazinone)s containing 4,4′‐isopropylidenediphenol and 4,4′‐(hexafluoroisopropylidene) diphenol and diphenyl ether linkage were soluble in chlorinated solvents such as chloroform. Other poly‐(phthalazinone)s were soluble in dipolar aprotic solvents such as N,N′‐dimethylacetamide. The soluble poly(phthalazinone)s can be cast as flexible films from solution. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2481–2490, 2003     

Phenylated imide–quinoxaline copolymers

Phenylated, ordered imide–quinoxaline copolymers of high oxidative-thermal stability were prepared by one-step solution condensation of aromatic tetraamines with N,N′-bis(4-benzilyl)pyromellitimide. Polymerization in m-cresol leads to high molecular weight polymers that remain soluble. Thermal gravimetric analysis and isothermal decomposition at 400°C shows that these polymers are as stable as polyimides or polyquinoxalines. The polymer decomposition temperatures range between 495 and 550°C, depending upon structure. Also, the rate of isothermal decomposition at 400°C in air showed a strong dependency of weight loss on structure. Tough films were cast from solution.     

Poly(arylene ether)s and poly(arylene thioether)s containing the 1,2-dihydro-4-phenyl(2H)- phthalazinone moiety

A series of new high molecular weight poly(arylene ether)s containing the 1,2-dihydro-4-phenyl(2H)phthalazinone moiety have been synthesized. The inherent viscosities of these polymers are in the range of 0.33–0.64 dL/g. They are amorphous and readily soluble in chloroform, DMF, and DMAc. The glass transition temperatures of the polymers range from 241 to 320°C and the 5% weight loss temperatures in nitrogen atmosphere range from 473 to 517°C. The hydroxy group in the monomer 1,2-dihydro-4-(4-hydroxyphenyl)(2H)phthalazin-1-one has been selectively transformed into the N,N′-dimethylthiocarbamate group, which was then rearranged to give the S-(N,N′-dimethylcarbamate) group via the Newman–Kwart rearrangement reaction. A series of poly(arylene thioether)s containing the 1,2-dihydro-4-phenyl(2H)phthalazinone moiety have also been synthesized via two types of reactions, a N C coupling reaction and a one-pot reaction between the S-(N,N′-dimethylcarbamate) and activated dihalo compounds, in diphenyl sulfone in the presence of a cesium carbonate and calcium carbonate mixture. These poly(arylene thioether)s also have high glass transition temperatures (ranging from 217–303°C) and high thermal stabilities. Compared with their poly(ether) analogs, the poly(arylene thioether)s have glass transition temperatures several degrees lower, which is attributed to the more flexible C S C bonds. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36 : 455–460, 1998     

Preparation and properties of aromatic polyamide-esters from aminophenols and aromatic diacid chlorides

Aromatic polyamide-esters of moderately high molecular weight were prepared from various combinations of three aminophenols (m- and p-aminophenol, and 4-(4′-aminophenoxy) phenol) and two aromatic diacid chlorides (isophthaloyl and terephthaloyl) by interfacial polycondensation in a cyclohexanone/water system and two-phase polycondensation in a dichloromethane/water system with phase-transfer catalysts. The solution polycondensation in dichloromethane/N,N-dimethylacetamide was also successful for the production of high-molecular-weight polymers. The solubility of the aromatic polyamide-esters varied markedly with polymer structure. Except for two polyamide-esters derived from terephthaloyl chloride, all the other polymers were almost amorphous. These polymers had glass transition temperatures at around 200°C and showed 10% weight losses at about 400°C in both air and nitrogen atmospheres.     

Synthesis and characterisation of chiral liquid crystalline elastomers containing four-arm crosslinking agent

A new series of side-chain chiral liquid crystalline elastomers derived from M₁ (cholest-5-3-ol(3β)-4-(2-propen-yloxy)]benzoate) and M_C(2,5-[3,5-bis(4-(3-(4-(allyloxy)phenyl)propanoyloxy)benzoyloxy)benzoic acid]isosorbide diester). The structures of monomers and elastomers measured by using Proton Nuclear Magnetic Resonance Spectra (¹H-NMR) and Fourier transform infrared spectroscopy (FTIR) separately are consistent with our design. IIP~VIP all appeared blue Grandjean (GJ) texture on the heating cycle or cooling cycle. The glass sheets of IIP~VIP were made under 150°C and measured its ultraviolet–visible spectrophotometry by PerkinElmer Lambda 950 instrument (Shelton, CT, USA). IIP~VIP all have absorptions at about 481~483 and 561~562 nm. The optical activities were measured at different temperatures on heating and cooling cycles. And the blue selective reflection of IIP~VIP on the round glass sheet can be seen. The elastomers containing less than 6 mol% of the crosslinking units displayed elasticity, reversible phase transition and high thermal stability. The glass transition temperatures reduced first and then increased, the isotropisation temperatures and the mesophase temperature ranges increased first and then decreased with increasing content of crosslinking unit. The thermogravimetric analysis (TGA) results showed that the temperatures at which 5% weight loss occurred (T_d) were greater than 310°C for all the polymers.     

Thermotropic liquid‐crystalline polyesters of 4,4′‐biphenol and phenyl‐substituted 4,4′‐biphenols with 4,4′‐oxybisbenzoic acid

A series of thermotropic polyesters, derived from 4,4′‐biphenol (BP), 3‐phenyl‐4,4′‐biphenol (MPBP), and 3,3′‐bis(phenyl)‐4,4′‐biphenol (DPBP), 4,4′‐oxybisbenzoic acid (4,4′‐OBBA), and other aromatic dicarboxylic acids as comonomers, were prepared by melt polycondensation and were characterized for their thermotropic liquid‐crystalline (LC) properties with a variety of experimental techniques. The homopolymer of BP with 4,4′‐OBBA and its copolymers with either 50 mol % terephthalic acid or 2,6‐naphthalenedicarboxylic acid had relatively high values of the crystal‐to‐nematic transition (448–460 °C), above which each of them formed a nematic LC phase. In contrast, the homopolymers of MPBP and DPBP had low fusion temperatures and low isotropization temperatures and formed nematic melts above the fusion temperatures. Each of these two polymers also exhibited two glass‐transition temperatures, which were associated with vitrified noncrystalline (amorphous) regions and vitrified LC domains, as obtained directly from melt polycondensation. As expected, they had higher glass‐transition temperatures (176–211 °C) than other LC polyesters and had excellent thermal stability (516–567 °C). The fluorescence properties of the homopolymer of DPBP with 4,4′‐OBBA, which was soluble in common organic solvents such as chloroform and tetrahydrofuran, were also included in this study. For example, it had an absorption spectrum (λ_max = 259 and 292 nm), an excitation spectrum (λ_ex = 258 and 292 nm with monitoring at 350 nm), and an emission spectrum (λ_em = 378 nm with excitation at 330 nm) in chloroform. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 141–155, 2002     

A bicyclic conjugated diene monomer,tetrahydroindene, for cationic polymerization and a novel alicyclic hydrocarbon polymer with heat resistance

This study was directed toward the cationic polymerization of tetrahydroindene (i.e., bicyclo[4.3.0]‐2,9‐nonadiene), a bicyclic conjugated diene monomer, with a series of Lewis acids, especially focusing on the synthesis of high‐molecular‐weight polymers and subsequent hydrogenation for novel cycloolefin polymers with high service temperatures. EtAlCl₂ or SnCl₄ induced an efficient and quantitative cationic polymerization of tetrahydroindene to afford polymers with relatively high molecular weights (number‐average molecular weight > 20,000) and 1,4‐enchainment bicyclic main‐chain structures. The subsequent hydrogenation of the obtained poly(tetrahydroindene) with p‐toluenesulfonyl hydrazide resulted in a saturated alicyclic hydrocarbon polymer with a relatively high glass transition (glass‐transition temperature = 220 °C) and improved pyrolysis temperature (10% weight loss at 480 °C). The new diene monomer was randomly copolymerized with cyclopentadiene at various feed ratios in the presence of EtAlCl₂ to give novel cycloolefin copolymers, which were subsequently hydrogenated into alicyclic copolymers with variable glass‐transition temperatures (70–220 °C). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6214–6225, 2006     

Liquid-crystalline behaviour of 4-(ω-aminoalkyloxy)-4′-cyanobiphenyls and their side chain epoxy polymers

Abstract

Liquid-crystalline side chain polymers were obtained from the ring-opening reaction of epoxy resin with mesogenic amines, 4-(ω-aminoalkyloxy)-4′-cyanobiphenyl. The amines with the alkyl group ranging from five to nine methylene units were synthesized, and were found to exhibit an enantiotropic nematic phase. Polymerization of these amines with ethylene glycol diglycidyl ether at 100°C yielded the polymers of low glass transition and melting temperatures. The mesomorphic properties of the amines and the resulting epoxy polymers are reported.     

Synthesis and Characterization of Novel Poly(Arylene Ether)s from 4,4′‐Thiodiphenol

Four novel perfluoroalkylated poly(arylene ether)s have been synthesized successfully using four perfluoroalkyl‐activated bisfluoro monomers. These polymers are synthesized through nucleophilic displacement of the fluorine atoms on the benzene ring with 4,4′‐thiodiphenol and are named as 1a, 1b, 1c and 1d, respectively. The polymers obtained by displacement of the fluorine atoms exhibit weight‐average molar masses up to 3.9×10⁴ g · mol^?1 in Gel permeation chromatography. These poly(arylene ether)s showed very high thermal stability up to 548°C for 10% weight loss in TGA under nitrogen and high glass transition temperature (T_g) up to 178°C in DSC depending on the repeat unit structures. The glass transition temperatures taken as peak in tan δ in DMA measurements are in good agreement with the DSC T_g values. All the polymers synthesized are soluble in a wide range of organic solvent such as CHCl₃, CHCl₂, THF, NMP, DMF and toluene. Transparent thin films of these polymers cast from THF exhibited tensile strengths up to 72 MPa, modulus up to 1.69 GPa with low elongation at break depending on their exact repeating unit structures. Rheological properties showed ease of processability of these polymers with no change in melt viscosity with temperature.     

Preparation and Properties of Novel Aromatic Polyamides from Diamines Containing 4,5-Imidazolediyl Structure

Novel aromatic polyamides were prepared from aromatic diamine containing 4,5-imidazolediyl unit, either by low temperature solution polycondensation or by direct polycondensation. Used diamines were 4,5-bis(4-aminophenyl)-2-phenylimidazole 1, 4,5-bis[4-(4-aminophenyl)]-2-(4-methylphenyl)imidazole 2 and 4,5-bis[4-(4-aminophenoxy)phenyl]-2-phenylimidazole 3. The obtained aromatic polyamides were produced with moderate to high inherent viscosity and soluble in polar aprotic solvents such as N,N-dimethylacetamide (DMAc), 1-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). Thermogravimetric analysis showed those polymers were stable up to 422°C in nitrogen atmosphere. The glass transition temperature (T _g)s of the polymers derived from diamine 3 were in the range between 243 and 275°C, and these values were approximately 120–160°C lower than those analogue polyamide I series containing no phenoxy units. The properties of polyamide I series are also compared with those of analogue polymers that order of aromatic nuclei and amide linkage is reversible.     

Polycarbazole Copolymers from 3-(4-Fluorobenzoyl)carbazole and 4,4′-Biphenol via Combined C-N and C-O Coupling Reactions with Activated Difluorides

3-(4-Fluorobenzoyl)carbazole was synthesized by a Friedel-Crafts reaction of carbazole with 4-fluorobenzoylchloride. ¹H-NMR and MALDI-TOF MS confirmed the structure and the purity. Copolymers of these NH/OH-containing monomers were prepared with 4, 4′-biphenol and bis(4-fluorophenyl)sulfone as comonomers by combined C-O and C-N coupling reactions with activated difluorides. These copolymers were soluble in N-methylpyrrolidinone (NMP), dimethylsulfoxide (DMSO), N,N-dimethylacetamide (DMAc) and dimethylformamide (DMF). The inherent viscosities of the copolymers in NMP solutions at 30°C were all around 0.8 dL/g. They could be easily cast into tough films from NMP solutions. The copolymers exhibited T_gs ranging from 238°C to 282°C. Thermal stabilities by TGA showed no weight loss below 400°C and the temperatures of 5% weight loss ranged from 535°C to 558°C. The homopolymer of 3-(4-fluorobenzoyl)carbazole was insoluble in common solvents and had a T_g of 332°C, and temperature of 5% weight loss of 560°C. UV-VIS absorption and fluorescence of the polymers are also presented.     

Synthesis and characterization of aromatic poly(ether ketone)s containing cyclotriphosphazene units

Bis(4-oxybenzoic acid) tetrakis(phenoxy) cyclotriphosphazene (IUPAC name: 4-[4-(carboxyphenoxy)-2,4,6,6-tetraphenoxy-1,3,5,2λ⁵,4λ⁵,6λ⁵-triazatriphosphinin-2-yl]oxy-benzoic acid) was synthesized and direct polycondensed with diphenylether or 1,4-diphenoxybenzene in Eaton's reagent at the temperature range of 80–120°C for 3 hours to give aromatic poly(ether ketone)s. Polycondensations at 120°C gave polymer of high molecular weight. Incorporation of cyclotriphosphazene groups in the aromatic poly(ether ketone) backbone greatly enhanced the solubility of these polymers in common organic polar solvents. Thermal stabilities by TGA for two polymer samples of polymer series ranged from 390 to 354°C in nitrogen at 10% weight loss and glass transition temperatures (T_g) ranged from 81.4 to 89.6°C by DSC. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1227–1232, 1998     

BLUE LIGHT EMITTING COPOLY-(ARYLENE ETHER)S CONTAINING A 3,6- DIALKOXYPHTHALIMIDE GROUP

ABSTRACT

Four new bisphenols containing 3,6-dialkoxyphthalimide moieties were prepared in high yields. They were copolymerized with BPA or 2,5-bis(4-hydroxyphenyl)oxadiazole by reaction with decafluorobiphenyl and with NaH as base to give novel copoly(arylene ether)s. The resulting copolymers have glass-transition temperatures (Tg) ranging from 153 to 235°C and very good thermal stabilities with 5% wt loss temperatures (TGA) ranging from 378 to 499°C. These polymers show strong blue light emission in wavelengths ranging from 420 to 430 nm, while their UV absorption peaks vary from 368 to 383 nm. They have excellent solubility in common organic solvents.