Synthesis of asymmetrically substituted head‐to‐head polyacetylenes from 2,3‐disubstituted‐1,3‐butadienes

Asymmetrically substituted head‐to‐head polyacetylenes with phenyl and triphenylamine, thienyl or pyrenyl side groups were synthesized through anionic or controlled radical polymerization of 2,3‐disubstituted‐1,3‐butadienes and subsequent dehydrogenation process. Anionic polymerizations of the designed monomers bearing pendent triphenylamine and thienyl group gave narrow disperse disubstituted precursor polybutadienes with exclusive 1,4‐ or 4,1‐structure, which were confirmed by GPC and NMR measurements. In addition, the monomers possessing pyrenyl group were polymerized via nitroxide mediated radical polymerization and the resulting polymers were obtained with controlled molecular weight and low polydispersities. These polybutadiene precursors were then dehydrogenated in the presence of 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone. Thus asymmetrically substituted head‐to‐head polyacetylenes were obtained as indicated by ¹H NMR. The properties of polybutadiene precursors and the corresponding polyacetylenes were analyzed by UV–vis, DSC, and TGA. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 395–402     

Temperature‐dependent fluorescence from pyrenyl‐modified polyethylene films. A comparison of attachment methods and morphology changes by irradiation with eV‐range photons and bombardment with MeV‐range positive ions

1‐Pyrenyl groups were attached covalently to three polyethylene ( Py–PE ) films with different crystallinities by irradiating (eV‐range photons–UV‐photons) or by bombarding (MeV‐range ions–protons and alpha particles) pyrene‐doped PE films ( Py/PE ). Onset temperatures of relaxation processes (T_x) of the Py–PE were approximated from (1) Arrhenius‐type plots of the normalized integrated intensities of the films and (2) the temperature dependence of the full‐width half‐maximum (FWHM) films and the position of the 0–0 fluorescence band. DSC thermograms of the native and irradiated or bombarded films were also compared to independently assess the morphological changes. The onset temperatures T_x in lower crystallinity Py–PE films were more difficult to locate when prepared by bombardment with high doses than with low doses of photons or ions or by irradiation. The ease of locating the T_x in higher crystallinity Py–PE films was independent of dose, suggesting little change in the mobility in the vicinity of pyrenyl probes. Fluorescence from Py–PE bombarded with alpha particles indicated the presence of both singly‐ and doubly‐attached pyrenyl groups. The singly‐attached pyrenyl groups were less sensitive than the doubly attached to the T_x. Py–PE films were more sensitive luminescence reporters of T_γ segmental motions than were 9‐anthryl groups covalently attached to the same polymers. We also discuss possible reasons why the values of the activation energies for the relaxation processes, as calculated from the Arrhenius plots, were much smaller than those based on the dynamic mechanical methods. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2957–2970, 2004     

DEPTH PROFILES FOR PERMEATION OF WATER and OXYGEN IN VESICLES and TUBULE PHASES BY FLUORESCENCE QUENCHING STUDIES*

Static and dynamic fluorescence data from three structurally related probe molecules [(1-pyrenyl)acetic acid, 4-(l-pyrenyl)butanoic acid, and 12-(l-pyrenyl)dodecanoic acid] were employed to determine the influence of phase structure on oxygen and water permeability in small unilamellar vesicles and microtubules of l,2-bis(tricosa-10,12-diynoyl)-in-glycero-3-phosphocholine (DC₂₃PC). Since the pyrenyl units of the three reporter molecules probe environments at different depths in DC₂₃PC bilayers, the aggregated information provides a depth profile of both small-molecule permeability and order. The results indicate that the probe sites are somewhat more available to water molecules immediately below the chain melting transition temperature than above it: singlet lifetimes of the pyrenyl groups undergo a clear increase as the temperature is raised in the region of the transition. This observation is consistent with melted chains being able to wrap themselves more efficiently around pyrenyl units (and thereby protect them better from water molecules) than stiff chains. The gross picture that emerges is one in which pyrenyl groups experience water and oxygen quenching via opposing concentration gradients. The concentration of oxygen is greatest near the bilayer midplane and decreases toward the aqueous interface; the concentration of water increases from the midplane to the interface.     

Jumping Crystals of Pyrene Tweezers: Crystal‐to‐Crystal Transition Involving π/π‐to‐CH/π Assembly Mode Switching

Crystals of pyrene tweezers 1 with interdigitating pyrenyl blades jump vigorously at around 160 °C. Single‐crystal X‐ray diffraction analysis before jumping revealed the presence of a “pyrene tetrad” in the crystal lattice, where four pyrenyl blades are π ‐stacked on top of each other. Upon heating the crystal to induce the jumping event, inner two pyrenyl blades in the “pyrene tetrad” probably rotate to switch off their π ‐stacking interaction with the neighboring outer pyrenyl blades and form new CH−π bonds. Different from reported salient crystals, our crystal jumps with the release of CHCl₃ as inclusion solvent.     

Anionic alternating copolymerization of α‐arylacrylates with methyl methacrylate: Effect of monomer sequence on fluorescence

Anionic polymerizations of acrylates possessing 1‐pyrenyl (Py1), 1‐naphthyl (Np1), 2‐naphthyl (Np2), and 2‐fluorenyl (Fl2) groups as α‐substituents were investigated as well as the properties of the obtained polymers. Py1 and Np1 did not undergo polymerization, whereas Np2 and Fl2, annulated α‐phenylacrylates at 3,4‐position of the phenyl group, afforded homo‐oligomers and alternating copolymers with methyl methacrylate (MMA). The oligomer of Fl2 [oligo(Fl2)] exhibited strong excimer emission in diluted solution. In contrast, dominant monomer emission was observed for the alternating copolymer with MMA [poly(Fl2‐co‐MMA)]. In the alternating copolymer, MMA units could function as spacers preventing the association of pendant fluorene moieties to suppress the excimer formation. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2806–2814     

SYNTHESIS AND FLUORESCENCE STUDY OF St／DVB COPOLYMERS LABELLED WITH PYRENE GROUPS

ＳＹＮＴＨＥＳＩＳＡＮＤＦＬＵＯＲＥＳＣＥＮＣＥＳＴＵＤＹＯＦＳｔ／ＤＶＢＣＯＰＯＬＹＭＥＲＳＬＡＢＥＬＬＥＤＷＩＴＨＰＹＲＥＮＥＧＲＯＵＰＳＷａｎｇＧｕｏｃｈａｎｇ；ＬｉａｎｇＹｕａｎｆｏｎｇ；ＧａｏＨｕａｎ；ＬｉａｎｇＬｉｊｕｎ；ＨｅＢｉｎｇｌｉ...     

Synthesis and photophysical properties of polyethylene containing pyrenyl units in the side chain

Copolymerization of ethylene and diallyl‐bis(pyren‐1‐yl)‐silane (APyS) was investigated with zirconocene catalysts, rac‐ethylenebis(indenyl)zirconium dichloride ( 1 ) and diphenylmethylene(cyclopentadienyl)(9‐fluorenyl)zirconium dichloride ( 2 ), using methylaluminoxane as a cocatalyst. APyS was copolymerized via both 1,2‐insertion and cyclization insertion, and cyclization selectivity, ratio of cyclized insertion unit, of APyS in the copolymers obtained with Catalyst 1 was higher than that obtained with Catalyst 2 . Catalyst 2 showed a higher reactivity for APyS than Catalyst 1 . Photophysical properties of the copolymer were investigated by UV–vis and photoluminescence (PL) spectroscopy, and absorption and fluorescence derived from pyrenyl groups were detected in the copolymers. Chloroform solution of the copolymer showed emission derived from both monomer and eximer of pyrenyl units. Only the emission derived from eximer of pyrenyl units was observed in the cast film. The polarized PL spectrum of an oriented film showed anisotropy, and the polarization excitation parallel to the drawing direction showed high fluorescence intensity. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Photoinduced electron transfer at the polymer-solution interface. I. Surface property-reactivity relation

Photooxidation of leuco crystal violet(LCV) to the dye(CV⁺) by interfacial sensitization with polymer-bonded pyrenyl groups was studied. Poly(ethylene-g-acrylic acid) was esterified by 1-hydroxymethylpyrene in tetrahydrofuran (THF) (Film 1) or in acetonitrile (Film 2). Film 2 had a more condensed but thinner pyrene-containing surface layer than Film 1. Differences in surface structure were investigated by fluorescence and absorption spectra, as well as by measuring contant angle to water as a function of the total amount of bonded pyrene. Films 1 and 2 behaved differently in the photoreaction, which was interpreted as due to the difference in the affinity of LCV solution to the film surface, hence the diffusion of LCV into the film. The quantum efficiency of CV⁺ formation (?cv⁺) is therefore the function of the thickness of the photoabsorbing layer and the effective reaction volume determined by the depth of LCV diffusion. The role of excimer formation and energy migration among pyrenyl groups was concluded to be of minor importance.     

Electron-Transfer-Induced Self-Assembly of a Molecular Tweezer Platform

The design and synthesis of a new molecular tweezer ( T-tmp ) with electron-rich pincers are reported. The stable monocationic radicals and self-assembled dimeric radicals of this molecular tweezer platform were prepared by chemical oxidative titration. With the aid of DFT calculations, it was found that the dimeric radicals with syn-syn-syn conformer has the most stable structure, with the hole primarily delocalized between parallel stacked pyrenyl groups.     

Adduct Formation Between γ-Cyclodextrin and the Bifluorophore 1,3-Bis(1-pyrenyl)propane

The complexation of the bifluorophore 1,3-bis(pyrenyl)propane with γ-cyclodextrin in water has been studied by means of steady state and time-resolved fluorescence spectroscopy. It was found that in the association with γ-cyclodextrin the propane chain of 1,3-bis(pyrenyl)propane folds and the two pyrene units enter the same cyclodextrin cavity where they form weakly bound ground state dimers, which upon excitation emit excimer fluorescence. In addition to this 1:1 excimer emitting complex, two more complexes were detected, which emit monomer pyrene fluorescence. One has 1:1 stoichiometry, i.e. isomeric to the previous complex, and the other, with 2:1 stoichiometry, is comprised of two γ-cyclodextrin units and one 1,3-bis(pyrenyl)propane.     

An efficient synthesis of telechelic poly (N‐isopropylacrylamides) and its application to the preparation of α,ω‐dicholesteryl and α,ω‐dipyrenyl polymers

Poly(N‐isopropylacrylamide)s (PNIPAMs) with cholesteryl or pyrenyl moieties at each chain end (CH‐PNIPAMs or Py‐PNIPAMs) were prepared via end‐group modification of α,ω‐dimercapto poly(N‐isopropylacrylamides), ranging in molecular weight from ～ 7000 to 45,000 g mol^?1 with a polydispersity index of 1.10 or lower. The telechelic thiol functionalized PNIPAMs were obtained by aminolysis of α,ω‐di(isobutylthiocarbonylthio)‐poly(N‐isopropylacrylamide)s (iBu‐PNIPAMs) obtained by reversible addition‐fragmentation chain transfer (RAFT) polymerization of N‐isopropylacrylamide in the presence of the difunctional chain transfer agent, diethylene glycol di(2‐(1‐isobutyl)sulfanylthiocarbonylsulfanyl‐2‐methyl propionate) (DEGDIM). The self‐assembly of the polymers in water was assessed by fluorescence spectroscopy, using the intrinsic emission of Py‐PNIPAM or the emission of pyrene added as a probe in aqueous solutions of CH‐PNIPAM. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 314–326, 2008     

Syntheses and some fluorescence properties of poly(2-methacrylamido-3-arylpropionic acid)

2-Methacrylamido-3-arylpropionic acid, where aryl is 1-naphthyl (M1NpPA), 2-naphthyl (M2NpPA), or 1-pyrenyl (M1PyPA), was synthesized. Free radical polymerization gave polymers which were soluble in water at pH > 6. In aqueous solution, poly(M1NpPA) and poly(M2NpPA) exhibited strong excimer fluorescence as a dominant component, whereas poly(M1PvPA) showed weak monomer fluorescence as a main component. Excitation spectra and fluorescence quenching by Tl⁺ ions suggested that naphthyl groups in poly(M1NpPA) and poly(M2NpPA) interacted so as to form excimer sites, by which migrating excited singlets were trapped, leading to the strong excimer emission. It was suggested, however, that pyrenyl groups in poly(M1PyPA) were sterically so constrained that they could not attain the full-overlap excimer conformation but could only interact to form self-quenching sites, to which energy migration occurred, leading to weak fluorescence. © 1993 John Wiley & Sons, Inc.     

Multi-Directional Mechanofluorochromism of Acetyl Pyrenes and Pyrenyl Ynones

A series of acetyl pyrenes and pyrenyl ynones with and without tert-butyl groups showed distinct mechanofluorochromism (MFC). Four pairs of polymorphic solids were found out of six compounds and interestingly, each of them showed hypsochromic, bathochromic or off-to-on MFC. The MFC properties were rationalized by categorizing the packing schemes into herringbone, sandwich, beta and gamma motifs depending on the relative contributions of C⋅⋅⋅C (or π-π) against C⋅⋅⋅H contacts. The bulky tert-butyl and trimethylsilyl groups served not only to reduce the number of aggregation patterns but also to prohibit the complete back reactions in solid state. Our results suggest that the simple pyrene derivatives may be promising candidates for a novel group of mechanically-sensitive materials.     

Fluorescent probe for Zn2+ with light-harvesting pyrenyl groups: sensitization via intramolecular energy transfer

Abstract  

Bis[N-(1-pyrenylmethyl)salicylideneaminato]zinc(II) emits intense fluorescence on excitation of the pyrenyl group. This fluorescence originates from the excited state of the salicylideneamine moiety, indicating that efficient intramolecular energy transfer takes place. The occurrence of such efficient energy transfer is accounted for by significant spectral overlap between the emission from the S₁ state of the pyrenyl group and the absorption of the salicylideneamine–zinc complex.     

Intrapolymer charge separation induced by picosecond multiphoton excitation: polyesters with pendant 1-pyrenyl groups in DMF

Intrapolymer electron transfer from the higher excited to the neighbouring ground states of pyrenyl chromophores occurs rapidly in polyesters. This charge separation process is characteristic of polymers and was not observed in the studies on bichromophoric model compounds. Relative geometrical structures of the relevant chromophores are discussed by comparing the results with those of polypeptides having the same chromophore.     

Linear polymers of allyl acrylate and allyl methacrylate

Allyl acrylate and allyl methacrylate were polymerized by anionic initiators to soluble linear polymers containing allyl groups in the pendant side chains. The pendant unpolymerized allyl groups of the resulting linear poly(allyl acrylates) were shown to be present by: (1) the disappearance of the acrylyl and methacrylyl double bond absorptions in the infrared spectra in the conversions of monomers to polymers; (2) postbromination of the allyl bonds in the linear polymer; (3) the disappearance of the allyl groups absorptions in the infrared spectra of the brominated linear polymers; and (4) the thermal- and radical-initiated crosslinking of the linear polymers through the allyl groups. Allyl acrylate and allyl methacrylate show great reluctance to copolymerize with styrene under anionic initiation, but copolymerize readily with methyl methacrylate and acrylonitrile. Block copolymers were prepared by reacting allyl methacrylate with preformed polystyrene and poly(methyl methacrylate) anions. The linear polymers and copolymers of allyl acrylate may be classified as “self-reactive” polymers which yield thermosetting polymers. Bromination of the linear polymers offers a convenient method of producing self-extinguishing polymers.     

Self-assembly of zinc chlorophyll derivatives possessing a pyrenyl group at the 17-propionate residue and effects of additional γ-cyclodextrins on their optical properties

Two kinds of zinc 3¹-hydroxy-13¹-oxo-chlorins 1 and 2 possessing a pyrenyl group at the 17-propionate residue, of which the linker length between the chlorin and the pyrene moieties was varied, were synthesised from naturally occurring chlorophyll a, and were self-assembled in an aqueous solution. Both zinc chlorins 1 and 2 exhibited Q_y absorption bands around 720 nm accompanying circular dichroism signals in the Q_y region, indicating that these zinc chlorins could form self-aggregates like chlorosomes of green photosynthetic bacteria. Addition of γ-cyclodextrin into an aqueous solution containing the self-aggregates of zinc chlorin 1 esterified with 1-pyrenylmethanol induced the appearance of excimer emission of the pyrene moieties around 480 nm as well as increased the fluorescence intensities of the pyrene monomers at 378 and 396 nm, while only an increase in fluorescence from the monomeric pyrene moiety was observed in the case of 2 esterified with 4-(1-pyrenyl)butanol. Exogenous γ-cyclodextrin unchanged the spectral features derived from the chlorin moieties of 1 and 2 in the aqueous phase. These suggest that the encapsulation of the pyrenyl groups in the zinc chlorins unchanged their assembling states under the present conditions.     

RAFT‐based synthesis and the gelation property of telechelic polymers that can immobilize biomacromolecules

Telechelic polymers, macromolecules having two reactive end groups, can serve as building blocks for constructing polymers or polymeric materials that have complex architectures. Among the telechelic polymers, polymers bearing hydroxyl groups at two terminals have been used as components for preparation of functional materials. In the present study, RAFT polymerization of both N‐acryloylmorphorin and N‐succinimidyl acrylate by using a newly synthesized dithiobenzoate‐type chain transfer agent bearing hydroxyl groups at both terminals (HECPHD) was reported. After the acryloylation of the hydroxyl terminals of the obtained polymer, gelation was observed. Furthermore, the polymer could react with a protein via the conjugation of the succinimidyl esters‐containing polymers to the amino groups present on the protein surface. The results show that activated esters‐bearing polymers with hydroxyl groups at both terminals can be used as building blocks for constructing polymeric materials for an immobilization of biomacromolecules. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1356–1365     

Synthesis and Characterization of Ru(II) Complexes with π-Expansive Imidazophen Ligands for the Photokilling of Human Melanoma Cells

Ru(II) complexes were synthesized with π-expanding (phenyl, fluorenyl, phenanthrenyl, naphthalen-1-yl, naphthalene-2-yl, anthryl and pyrenyl groups) attached at a 1H-imidazo[4,5-f][1,10]phenanthroline ligand and 4,4′-dimethyl-2,2′-bipyridine (4,4′-dmb) coligands. These Ru(II) complexes were characterized by 1D and 2D NMR, and mass spectroscopy, and studied for visible light and dark toxicity to human malignant melanoma SK-MEL-28 cells. In the SK-MEL-28 cells, the Ru(II) complexes are highly phototoxic (EC₅₀ = 0.2–0.5 µm ) and have low dark toxicity (EC₅₀ = 58–230 µm ). The highest phototherapeutic index (PI) of the series was found with the Ru(II) complex bearing the 2-(pyren-1-yl)-1H-imidazo[4,5-f][1,10]phenanthroline ligand. This high PI is in part attributed to the π-rich character added by the pyrenyl group, and a possible low-lying and longer-lived ³IL state due to equilibration with the ³MLCT state. While this pyrenyl Ru(II) complex possessed a relatively high quantum yield for singlet oxygen formation (Φ_∆ = 0.84), contributions from type-I processes (oxygen radicals and radical ions) are competitive with the type-II (¹O₂) process based on effects of added sodium azide and solvent deuteration.     

On the Tacticity of Polynorbornenes with 5,6‐endo Pendant Groups That Contain Substituted Aryl Chromophores

Two dimers and a series of polymers with 5,6‐endo pendant aryl groups that contain different substituents at the para positions were synthesized. The conformation and stereochemistry of the dimers and polymers were determined by nonlinear optical analysis (EFISH) as well as UV/Vis and ¹³C NMR spectroscopy. The chemical shifts of C7 for the polymers appeared as two peaks in the ¹³C NMR spectra when the substituents are electron‐withdrawing groups. The percentage decrease in the relative extinction coefficient of the polymers, ε_d, was linearly related to the Hammett constant σ. Polynorbornenes with electron‐withdrawing substituents may adopt isotactic stereochemistry with all pendant groups aligned in one direction. The nature of the interactions between neighboring chromophores may be one of the most important factors in directing the stereoregularity and conformation of these polymers. The corresponding polymers derived from the exo isomers appeared to be less stereoregular.