Phenylacetylene Units Research Articles

Rod-shaped cyanoacrylic derivatives with D-π-A architecture: synthesis, thermal, photophysical and theoretical studies

ABSTRACT Two dyes, 4 and 5, bearing an alkoxy group as a donor connected to cyanoacrylic acid acceptor/anchoring group bridged by the phenylacetylene unit were designed and synthetised through Knoevenagel condensation between aromatic aldehydes and cyanoacetic acid reagent. The dyes were characterised using FT-IR, 1H-NMR, 13C-NMR, ESI-HRMS and polarised optical microscopy, absorption and fluorescence techniques. Nematic mesophase was identified for both rod-shaped dyes. During heating at high temperatures (>200°C), the dyes exhibited marked thermal instability which resulted in material decomposition. The photophysical properties of the compounds were investigated in chloroform as well as their absorption, emission spectra in solid state. Solvatochromism was analysed and the mechanism of fluorescence quenching was performed using fullerene pyrrolidine tris-acid ethyl ester PyC 60 as a receptor. The fluorescence quenching studies suggested charge transfer process from dyes 4 and 5 to PyC 60 , where the bimolecular rate constant k q was larger for 4 than 5, showing that the phenyl group performed better than the naphthyl group. The energy band gap predicted with DFT calculations agreed with the experimental data. Natural transition orbitals (NTOs) analysis revealed that S1 states for 4 and 5 in gas phase have a predominantly local-excitation (LE) nature.

Ultra-stable fluorescent 2D covalent organic framework for rapid adsorption and selective detection of radioiodine

Abstract Radioactive iodine is a harmful substance produced by nuclear fission, and its hazard to the human body should not be underestimated. In this work, a novel adsorbent COF-PA containing quinoline and phenylacetylene units for dual chemical adsorption of iodine is designed and prepared. It exhibits the fastest adsorption rate (1.3 g h−1) among 2D covalent organic frameworks and also possesses remarkable adsorption capacity and efficiency at low concentration of iodine vapor. When the weight ratio of adsorbent to iodine is 1:1, the adsorption efficiency of COF-PA reaches 90%. Moreover, COF-PA can maintain good crystallinity when soaked in common organic solvents and strong acids (12 M HCl) and bases (14 M NaOH) for one week, and its stability is of great significance for the real industrial applications. Unexpectedly, COF-PA shows strong fluorescence, which can be specifically quenched by iodine and thus be applied for selective iodine detection.

Synthesis, characterization and optical properties of a series of copolymers bearing 1-ethynylpyrene and ethynylbenzene units

AbstractA novel series of copolymers were obtained from the copolymerization of 1-ethynylpyrene (EP) (known as pyrenylacetylene) and ethynylbenzene (EB) (named also phenylacetylene) with WCl6 as catalyst and toluene as solvent, using different monomer molar ratios EP/EB (80:20, 60:40, 50:50; 40:60, 20:80). The optical properties of the obtained copolymers Poly(EP-co-EB) were determined by absorption and fluorescence spectroscopy. Absorption spectra of the copolymers Poly(EP-co-EB) showed that copolymers containing phenylacetylene units possess a lower degree of conjugation than the homopolymer trans-poly(1-ethynylpyrene) (trans-PEP), since they showed a twisted conformation. These results were confirmed by emission spectroscopy showing the formation of excimers for those copolymers containing high pyrene content.

Monitoring intracellular metal ion complexation with an acetylene-tagged ligand by Raman spectroscopy.

We propose to monitor molecular vibrations to identify metal ion–ligand complexation by means of Raman spectroscopy, which has been applied to track vibrational modes of molecules and to obtain a structural fingerprint. We prepared ligand molecules for Zn2+ ion complexation with a dipycolylaminoethyl aniline (DPEA) skeleton and phenylacetylene unit as the Raman tag which showed a typical band around 2200 cm−1. Among the labeled ligands synthesized in this study, A-DPEA showed a strong band attributed to the acetylene unit at 2212 cm−1, while the addition of Zn2+ ion resulted in a band shift to 2220 cm−1 due to complex formation. The addition of other metal ions and titration experiments showed that A-DPEA bound with Zn2+ selectively with a dissociation constant (Kd) that was estimated to be 0.22 μM. We also conducted cellular experiments and found that complexation between A-DPEA and Zn2+ also occurred in cells, with a shift in the Raman signal of the ligand from 2212 to 2215 cm−1. Thus, complex formation of the metal ion was identified by monitoring the Raman band shift.

Synthesis and Magnetic Properties of Stable Radical Derivatives Carrying a Phenylacetylene Unit.

A nitronyl nitroxide derivative, 2-phenylethynyl-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl-3-oxide (1), and two verdazyl derivatives carrying a phenylacetylene unit, 1,5-diphenyl-3-phenylethynyl-6-oxo-1,2,4,5-tetrazin-2-yl (2) and 1,5-diisopropyl-3-phenylethynyl-6-oxo-1,2,4,5-tetrazin-2-yl (3), were synthesized and their packing structures were studied by X-ray crystallographic analysis and magnetically characterized in the solid state. While 1 and 3 had an isolated doublet spin state, 2 formed an antiferromagnetically coupled pair (2J/kB = −118 K). Density functional theory (DFT) calculations reveal that the spin density polarized in the phenyl group decreases as the dihedral angle between the phenyl ring and radical plane increases.

Efficient reverse saturable absorption of sol-gel hybrid plasmonic glasses

Monolithic silica sol-gel glasses doped with platinum(II) acetylide complexes possessing respectively four or six phenylacetylene units (PE2-CH2OH and PE3-CH2OH) in combination with various concentrations of spherical and bipyramidal gold nanoparticles (AuNPs) known to enhance non-linear optical absorption, were prepared and polished to high optical quality. The non-linear absorption of the glasses was measured and compared to glasses doped solely with AuNPs, a platinum(II) acetylide with shorter delocalized structure, or combinations of both. At 532 nm excitation wavelength the chromophore inhibited the non-linear scattering previously found for glasses only doped with AuNPs. The measured non-linear absorption was attributed to reverse saturable absorption from the chromophore, as previously reported for PE2-CH2OH/AuNP glasses. At 600 nm strong nonlinear absorption was observed for the PE3-CH2OH/AuNPs glasses, also attributed to reverse saturable absorption. But contrary to previous findings for PE2-CH2OH/AuNPs, no distinct enhancement of the non-linear absorption for PE3-CH2OH/AuNPs was observed. A numerical population model for PE3-CH2OH was used to give a qualitative explanation of this difference. A stronger linear absorption in PE3-CH2OH would cause the highly absorbing triplet state to populate quicker during the leading edge of the laser pulse and this would in turn reduce the influence from two-photon absorption enhancement from AuNPs.

Synthesis, Characterization, Electrical Conductivity and Fluorescence Properties of Polyimine Bearing Phenylacetylene Units.

In this study, a Schiff base was synthesized by the condensation reaction of 4-bromobenzaldehyde and 4-aminophenol. Then, phenylacetylene substituted Schiff base monomer (IPA) was obtained by HBr elimination reaction of IPA with phenylacetylene through Sonogashira reaction. IPA was polymerized via chemical oxidative polycondensation reaction. FT-IR and NMR measurements were used for the structural analyses of the synthesized substances. Fluorescence and UV-Vis analyses were carried out for optical characterization. Electrochemical characteristics, electrical conductivities and thermal properties were determined using cyclic voltammetry (CV), four-point probe conductometer, TG-DTA and DSC methods. The main purpose of the present study was to investigate the effects of phenylacetylene bearing units on the properties of conjugated aromatic polyimines. The spectral analysis signified a green light emission behavior when irradiated at different wavelengths. Combined with fluorescent behavior and good thermal stability, the electrical conductivity was found to be very crucial for π-conjugated polymer.

BODIPY-phenylacetylene macrocycle motifs for enhanced light-harvesting and energy transfer applications

BODIPY-phenylacetylene macrocyclic hybrids are reported, where energy transfer is observed from the phenylacetylene unit to the BODIPY core.

Understanding the two-photon absorption spectrum of PE2 platinum acetylide complex.

Herein, we report on the two-absorption cross-section spectrum of trans-Pt(PBu3)2 (C≡C-C6H4-C≡C-C6H5)2 (PE2) platinum acetylide complex employing the femtosecond wavelength-tunable Z-scan technique. The PE2 complex can be visualized as two branches containing two phenylacetylene units, each one linked by a platinum center, completely transparent in the visible region. Because of this structure, large delocalization of π-electrons allied to the strong intramolecular interaction between the branches is expected. The 2PA absorption spectrum was measured using the femtosecond wavelength-tunable Z-scan technique with low repetition rate (1 kHz), in order to obtain the 2PA spectrum without excited-state contributions. Our results reveal that PE2 in dichloromethane solution presents two 2PA allowed bands located at 570 and 710 nm, with cross section of about 320 and 45 GM, respectively. The first one is related to the strong intramolecular interaction between the molecule's branches due to the presence of platinum atom, while the second one is associated with the breaking of symmetry of the chromophore in solution due, most probably to a large twisting angle of the ligand's phenyl rings relative to the Pt core.

Solvent assisted fluorescence modulation of a C3-symmetric organogelator

The synthesis and self-assembling properties of C3 symmetric donor–acceptor molecules containing 1,3,4-oxadiazole and bisthiophene moieties in the core functionalized with octyl (BTOX8) and dodecyl (BTOX12) substituted phenyl acetylene units at the periphery are reported. BTOX8 was found to form gels only in aliphatic solvents, whereas BTOX12 formed gels in both aliphatic and aromatic solvents. Photophysical analysis of BTOX12 solutions showed a striking effect of the solvent on the nature of the self-assembled aggregate formed. Our studies indicate that in aliphatic solvents such as n-decane the solvent molecules interact mainly with the alkyl regions of BTOX12. As a result the π–π interaction between the neighbouring molecules becomes feasible resulting in strong excitonic coupling between the neighbouring molecules leading to excimer type emission. In aromatic solvents the solvent molecules interact mainly with the chromophoric part of BTOX12 resulting in reduced π-stacking between the molecules in the aggregate leading to monomer type emission. Films prepared from aliphatic and aromatic solvents exhibited photophysical properties significantly similar to those observed in the respective solvents. Photophysical studies of the films indicated that the films prepared from n-decane exhibited an H-type molecular arrangement whereas the films prepared from toluene exhibited a slipped stack J-type arrangement.

Oligo(p‐phenylene ethynylene)–BODIPY Derivatives: Synthesis, Energy Transfer, and Quantum‐Chemical Calculations

The synthesis and energy-transfer properties of a series of oligo(p-phenylene ethynylene)-BODIPY (OPEB) cassettes are reported. A series of oligo(p-phenylene ethynylene)s (OPEs) with different conjugated chain lengths as energy donor subunit in the energy-transfer system were capped at both ends with BODIPY chromophores as energy-acceptor subunits. The effect of the conjugated chain of OPEs on energy transfer in the OPEB cassettes was investigated by UV/Vis and fluorescence spectroscopy and modeling. With increasing number n of phenyl acetylene units (n=1-7), the absorption and emission maxima of OPEn are bathochromically shifted. In the OPEBn analogues, the absorption maximum assigned to the BODIPY moieties is independent of the length of the OPE spacer. However, the relative absorption intensity of the BODIPY band decreases when the number of phenyl acetylene units is increased. The emission spectra of OPEBn are dominated by a band peaking at 613 nm, corresponding to emission of the BODIPY moieties, regardless of whether excitation is at 420 or 550 nm. Furthermore, a very small band is observed with a maximum between 450 and 500 nm, and its intensity relative to that of the BODIPY emission increases with increasing n, that is, the excited state of OPE subunits is efficiently quenched in OPEBn by energy transfer to the BODIPY moieties. Energy transfer (ET) from OPEn to BODIPY in OPEBn is very efficient (all Φ(ET) values are greater than 98 %) and only slightly decreases with increasing length of the OPE units. These results are supported by theoretical studies that show very high energy transfer efficiency (Φ(ET) >75 %) from the OPE spacer to the BODIPY end-groups for chains with up to 15-20 units.

Computational studies on cyclic [n]paraphenyleneacetylenes using homodesmotic reactions

Cyclic [n]paraphenyleneacetylenes ([n]CPPAs) are potentially useful compounds for molecular electronics. In this article, a homodesmotic reaction scheme coupled with density functional theory has been used to estimate theoretically strain energies and heats of formation of [n]CPPAs. Calculations have been done for a series of [n]CPPAs, containing up to ten phenylacetylene units. Strain energies of [n]CPPAs decrease, while heats of formation increase steadily with the increase in the number of phenylacetylene units using homodesmotic reaction schemes. B3LYP and mPW1PW91 functionals have been used with the Pople basis set 6-31G* to analyze the trends. The results are sensitive to the scheme of homodesmotic reaction chosen, thereby necessitating careful chemical consideration before spending considerable computational resources for higher [n]CPPAs not considered here. Computational estimates for the ring diameter of [n]CPPAs and absolute entropy have also been obtained here. The HOMO-LUMO gaps of the belt shaped [n]CPPAs show an odd–even difference. In addition, the HOMOs of the [3]CPPA, [5]CPPA, [7]CPPA and [9]CPPA are doubly degenerate.

Rigidity−Stability Relationship in Interlocked Model Complexes Containing Phenylene-Ethynylene-Based Disubstituted Naphthalene and Benzene

Structural rigidity has been found to be advantageous for molecules if they are to find applications in functioning molecular devices. In the search for an understanding of the relationship between the rigidity and complex stability in mechanically interlocked compounds, the binding abilities of two π-electron-rich model compounds (2 and 4), where rigidity is introduced in the form of phenylacetylene units, toward the π-electron deficient tetracationic cyclophane, cyclobis(paraquat-p-phenylene) (CBPQT^(4+)), were investigated. 1,4-Bis(2-(2-methoxyethoxy)ethoxy)-2,5-bis(2-phenylethynyl)benzene 2 and 1,5-bis(2-(2-methoxyethoxy)ethoxy)- 2,6-bis(2-phenylethynyl)naphthalene 4 were synthesized, respectively, from the appropriate precursor dibromides 1 and 3 of benzene and naphthalene carrying two methoxyethoxyethoxy side chains. The rigid nature of the compounds 2 and 4 is reflected in the reduced stabilities of their 1:1 complexes with CBPQT^(4+). Binding constants for both 2 (100 M^(-1)) and 4 (140 M^(-1)) toward CBPQT^(4+) were obtained by isothermal titration microcalorimetry (ITC) in MeCN at 25 °C. Compounds 1-4 were characterized in the solid state by X-ray crystallography. The stabilization within and beyond these molecules is achieved by a combination of intra- and intermolecular [C-H· · · O], [C-H· · ·π], and [π-π] stacking interactions. The diethyleneglycol chains present in compounds 1-4 are folded as a consequence of both intra- and intermolecular hydrogen bonds. The preorganized structures in both precursors 1 and 3 are repeated in both model compounds 2 and 4. In the structures of compounds 2 and 4, the geometry of the rigid backbone is differentsthe two terminal phenyl groups are twisted with respect to the central benzenoid ring in compound 2 and roughly perpendicular to the plane central naphthalene core in compound 4. To understand the significantly decreased stabilities of these complexes toward rigid guest molecules, relative to more flexible systems, we performed density functional theory (DFT) calculations using the newly developed M06-suite of density functionals. We conclude that the reduced binding abilities are a consequence of electronic and not steric factors, originating from the extended delocalization of the aromatic system.

Formation of chiral 2 1-helical columnar host system with phenylacetylene unit by using (1 R,2 S)-2-amino-1,2-diphenylethanol

A tunable supramolecular phenylacetylene host system with a chiral channel-like cavity is developed by using (1 R,2 S)-2-amino-1,2-diphenylethanol. This host system possesses a chiral 2 1-helical columnar structure; chiral cavities are constructed by the self-assembly of the 2 1-helical column, and guest molecules are included by varying the packing of this column.

Towards a Better Understanding of Magnetic Interactions within m‐Phenylene α‐Nitronyl Nitroxide and Imino Nitroxide Based Radicals, Part III: Magnetic Exchange in a Series of Triradicals and Tetraradicals Based on the Phenyl Acetylene and Biphenyl Coupling Units

The present work completes and extends our previous reports on the determination of the magnetic ground state and on the strength of the through bond exchange coupling within series of biradicals. This knowledge was subsequently exploited for the analysis of the magnetic interactions in their crystals. We report here the studies of series of triradicals incorporating alpha-nitronyl nitroxides (NN) or alpha-imino nitroxides (IN) as terminal radical fragments connected through a m-phenylene coupling unit in one case and a phenyl acetylene unit in other case. Tetraradical derivatives have also been studied. The studies of isolated molecules (EPR in solution and DFT calculations) allow the assessment of the magnetic interactions through the magnetic coupling unit. All triradical derivatives are found to exhibit a quartet ground state, whereas a singlet ground state is determined for the tetraradical. This last result reinforces previous findings that the singlet ground state is favoured in related biradicals involving similar m-phenylene couplers. Moreover, the through bond magnetic exchange coupling for the ortho-meta connectivity could be demonstrated as being ferromagnetic, thus ascertaining our previous hypotheses. The magnetic properties of the triradicals and tetraradicals in their solid state have been rationalized by using a previously proposed methodology, allowing to identify the most relevant magnetic pathways.

Electronic structures and band gaps of chains and sheets based on phenylacetylene units

Abstract We investigate the electronic structures of polymers composed of π-conjugated phenylacetylene (PA) units, m -PA-based and p -PA-based wires, at the extended Huckel level of theory. It is demonstrated that these conjugated systems should have a variety of electric conductance. All of the one-dimensional (1D) chains and the two-dimensional (2D) sheet based on the m -PA unit are insulators with large band gaps of 2.56 eV because there is no effective orbital interaction with neighboring chains. On the other hand, p -PA-based 1D chains have relatively small band gaps that decrease with an increase in chain width (1.17–1.74 eV) and are semiconductive. The p -PA-based sheet called “graphyne”, a 2D-limit of the p -PA-based 1D chains, shows a small band gap of 0.89 eV. The variety of band electronic structures is discussed in terms of frontier crystal orbitals.

Identification of the light-absorbing states in tolane with potential relevance to self-similar phenylacetylene dendrimers

We report the observation and analysis of the high resolution fluorescence excitation spectrum of tolane (or diphenylacetylene, DPA) in a molecular beam. This analysis shows that the first one-photon-allowed state in DPA has 1 B 1 u symmetry, a consequence of exciton-like coupling between the two 1 L a states of the connected phenylacetylene (PA) units. The resulting long-axis polarization of the 1 B 1 u – 1 A g transition of each linear segment is responsible for the diverse optical properties of PA dendrimers.

The Relationship Between Molecular Structure and Spectroscopic Properties of a Series of Transition Metal-Containing Phenylacetylene Oligomers and Polymers

ABSTRACTTo develop novel nonlinear dyes for photonic applications, we synthesized a series of transition metal-containing phenylacetylene oligomers and polymers. The optical properties of these compounds were measured by UV/Vis, fluorescence, and flash photolysis experiments. As the number of oligomer units increased, the transition energies decreased. A solvatochromism experiment suggested the fluorescing state was different from the absorbing state. As a group, the spectra of the polymeric versions of these complexes were red shifted from the spectra of the oligomers. The polymeric complexes had less clear trends relating the number of oligomer units to transition energies. A comparison of a low molecular weight and a high molecular weight polymer showed the degree of polymerization caused spectroscopic shifts comparable to the number of phenylacetylene units in the monomer unit.

Reactivity of the nitro-group of a π-conjugated polymer upon the interface formation with chromium: a photoelectron spectroscopy investigation

X-ray photoelectron spectroscopy was used in order to investigate the interface formation between chromium and thin films of a newly synthesised π-conjugated polymer P(PA- pNO 2PA); the investigated material is a block copolymer consisting of phenylacetylene (PA) and para-nitro phenylacetylene ( pNO 2PA) units {[–(CHC–R) n –(CHC–R′) m –] N ; RC 6H 5, R′C 6H 4NO 2}. Chromium was evaporated stepwise in situ onto the polymer surface and the XPS spectra of the substrate polymer and of the metal overlayer were studied as a function of increasing chromium thickness. In the early stages of the interface formation, chromium was found to interact mainly with the nitrogen atoms of the –NO 2 groups, that are reduced to nitride-like species; the N–O bond is broken, as evidenced by the modifications occurring in the N1s and O1s spectra. The changes in the C1s spectra upon increasing metal deposition suggest the formation of a chromium–arene π-complex at low chromium coverage and of carbide-like species at higher chromium thickness.

Optical excitations in fractal antenna supermolecules with conjugated electrons: extended dendrimers

Abstract A coupled dipole model is proposed in order to characterize optical excitations in dendrimer supermolecules: the extended dendrimers. The dendrimer is composed of phenyl-ring vertexes and legs with phenyl rings and acetylene units. A transition dipole moment is assigned at each phenyl ring and the nearest-neighbor hopping integral is considered between the neighboring dipoles. The decreasing optical excitation energy with respect to the dendrimer size indicates the presence of exciton pathways along the backbone of the dendrimers.