Pyridine Chromophore Research Articles

Synthesis and photophysical properties of pyridyl- and quinolinyl-substituted bis(arylthienyl)pyridines

Two series of V-shaped 6,7-dihydro-5H-cyclopenta[c]pyridine chromophores bearing two 5-arylthiophen-2-yl fragments as well as pyridyl or quinolinyl residue have been designed and synthesized. The basic photophysical properties of the compounds have been investigated both in solutions and the solid state. 3,4-Bis(5-(4-diethylaminophenyl)thiophen-2-yl)-1-(quinolin-2-yl)-6,7-dihydro-5H-cyclopenta[c]pyridine 2a demonstrated positive emission solvatochromism, and the collected data were analyzed by using Lippert-Mataga equation, as well as Kosower and Dimroth/Reichardt scales. The ability to detect metal cations has been analyzed for the obtained heterocycles. It is found that addition of 1.5 eq of Cu2+ to diphenylamino-substituted chromophore 1b lead to totally luminescence quenching and solution of chromophore 1b turns dark yellow that can be seen with the naked eye. Additionally, halochromic properties have been examined, it was shown that diethylamino derivatives 1a and 2a demonstrated blue shifts in both absorption and emission spectra upon the treatment with TFA. Also, we checked emission behavior of chromophore 1a in MeCN–water mixtures with different water volume fractions. Finally, DFT calculations have been performed and according data, the replacement of pyridyl residue with quinolinyl one in studied heterocyclic ensembles leads to decrease in the value of energetic gap.

Conformer Specific Ultraviolet and Infrared Detection of Nicotine in the Vapor Phase.

A gas-phase electronic spectrum of nicotine in a supersonic expansion has been recorded using two-color resonant two-photon ionization spectroscopy. Efficient photoionization was achievable only via the pyridine chromophore owing to poor Franck-Condon overlap in the N-methylpyrrolidine moiety. Two conformers of nicotine have been characterized and assigned by infrared-ultraviolet (IR-UV) ion depletion and IR-UV hole-burning spectroscopy, in combination with quantum chemical techniques. Trans-A with nitrogen atoms further apart is more stable by 2 kJ mol-1 and the most populated conformer in the supersonic jet, owing this stability to a stronger inter-ring CH···N hydrogen bond than the trans-B counterpart.

Design of Novel, Water Soluble and Highly Luminescent Europium Labels with Potential to Enhance Immunoassay Sensitivities.

To meet the continual demands of more-sensitive immunoassays, the synthesis of novel luminescent Eu(III) chelate labels having similar substituted 4-(phenylethynyl)pyridine chromophores in three different chelate structure classes are reported. Significantly enhanced luminescence intensities were obtained, evidently caused by the intra-ligand charge transfer (ILCT) mediated sensitization, but the alternative ligands triplet state process cannot be ruled out. Based on the present study, even quite small changes on the chelate structure, and, especially, on the substituents’ donor/acceptor strength on both ends of 4-(phenylethynyl)pyridine subunits have an unpredictable effect on the luminescence. The highest observed brightness was 16,400 M−1 cm−1 in solution and 69,500 M−1 cm−1 on dry surface, being 3.4 and 8.7 fold higher compared to the reference chelate. The new label chelates provide solutions for improved assay sensitivity up-to tenfold from the present concepts.

Fast and Reversible Humidity-Responsive Luminescent Thin Films

Highly sensitive stimuli-responsive fluorescent films are playing an increasingly important role in the development of smart sensors and erasable optical devices. However, systems involving humidity-responsive fluorescence (HRF) are still very limited compared to those responsive to other common environmental stimuli (e.g., light, heat, pressure, or pH). Herein, by incorporating the 4-[4-(dimethylamino)styryl]pyridine chromophore into a polyvinylpyrrolidone host, we have developed new flexible self-supporting nanofiber films that exhibit fast and obvious HRF. The reversible transformation between two fluorescence states can be easily observed and recycled at least 200 times. Fluorescence microscopy images provided in situ evidence of changes in both fluorescence and morphology. This work therefore offers an alternative to conventional humidity sensors based on changes in color and electrical properties. Furthermore, we anticipate that these HRF films can also be employed as optical antiforgery materials.

Photoinduced oxidation of water in the pyridine-water complex: comparison of the singlet and triplet photochemistries.

It has recently been shown that low-lying dark charge-separated singlet excited states of nπ* and ππ* character exist in the hydrogen-bonded pyridine-water complex in addition to the familiar nπ* and ππ* excited states of the pyridine chromophore. The former have been shown to promote the transfer of a proton from water to pyridine, resulting in the pyridinyl-hydroxyl radical pair. In the present work, the potential-energy surfaces of the triplet excited states of the pyridine-water complex have been explored with the same ab initio electronic-structure methods (ADC(2), CASPT2). Minimum-energy reaction paths for excited-state H atom transfer, energy surfaces in the vicinity of the barrier for H atom transfer, as well as multistate surface crossings have been characterized. The photochemical reaction mechanisms on the singlet and triplet potential-energy surfaces are compared, and their relevance for photoinduced water oxidation with the pyridine chromophore are discussed.

Rapid optical methods for enantiomeric excess analysis: from enantioselective indicator displacement assays to exciton-coupled circular dichroism.

CONSPECTUS: The advent of high-throughput screening (HTS) for chiral catalysts has encouraged the development of fast methods for determining enantiomeric excess (ee). Traditionally, chromatographic methods such as chiral HPLC have been used for ee determination in HTS. These methods, however, are not optimal because of high duty cycle. Their long analysis time results in a bottleneck in the HTS process. A more ideal method for HTS that requires less analysis time such as chiroptical methods are thus of interest. In this Account, we summarize our efforts to develop host-guest systems for ee determination. The first part includes our enantioselective indicator displacement assays (eIDAs), and the second part focuses on our circular dichroism based host-guest systems. Our first eIDA utilizes chiral boronic acid receptors, along with prescreened indicators, to determine ee for chiral α-hydroxyacids and vicinal diols with ±7% average error (AE). To further the practicality for this system, a HTS protocol was developed. Our second eIDA uses diamino chiral ligands and Cu(II) as the receptor for the ee determination of α-amino acids. The system reported ±12% AE, and a HTS protocol was developed for this system. Our first CD based host-guest system uses metal complexes composed of Cu(I) or Pd(II) with enantiopure 2,2'-diphenylphosphino-1,1'-binaphthyl (BINAP) as host to determine the ee of chiral vicinal diamines (±4% AE), primary amines (±17% AE), and cyclohexanones (±7% AE). Primary amines and cyclohexanones were derivatized to form chiral imines or chiral hydrazones to allow coordination with the metal complex. Upon coordination of chiral analytes, the metal-to-ligand (BINAP) charge transfer band was modulated, thus allowing the discrimination of chiral analytes. As an effort to improve the accuracy for chiral primary amine ee determination, a system with a host composed of o-formylphenyl boronic acid (FPBA) and enantiopure 1,1'-bi-2-naphthol (BINOL) was used to reduce the AE to ±5.8%. In the presence of amines, the FPBA-BINOL host forms an imine-coordinated boronic ester, thus affecting the CD signal of the boron complex. Another chiral primary amine ee determination system was developed with Fe(II) and 3-hydroxy-2-pyridinecarbaldehyde. The chiral imines, formed by the pyridinecarbaldehyde and chiral amines, would coordinate to the Fe(II) ion yielding exciton-coupled circular dichroism (ECCD) active metal complexes. This system was able to determine the ee of chiral amines with ±5% AE. Furthermore, this imine-Fe(II) complex system also successfully determined the ee of α-chiral aldehydes with ±5% AE. Other ECCD based hosts were subsequently developed; one with bisquinolylpyridylamine and Cu(II) for chiral carboxylates and amino acids and another multicomponent system with pyridine chromophores for chiral secondary alcohol ee determination. Both of the systems were able to determine ee of the chiral analytes with ±3% AE. Overall, our group has developed ee determining host-guest systems that target various functionalities. To date, we are able to determine the ee of vicinal diols, α-hydroxyacids, vicinal diamines, cyclohexanones, amines, α-chiral aldehydes, carboxylates, amino acids, and secondary alcohols with ±7% or lower average error. Future development will involve improving the average error and employing the current systems to analyze real-life samples resulting from parallel syntheses.

Computational investigation of the photoinduced homolytic dissociation of water in the pyridine–water complex

The photochemistry of the hydrogen-bonded pyridine-water complex has been investigated with ab initio computational methods. Vertical excitation energies, excited-state reaction paths for proton transfer as well as structures and energies of conical intersections and reaction barriers have been determined with multi-configuration self-consistent-field and multi-reference perturbation methods, as well as with single-reference coupled-cluster and propagator methods. In the pyridine-water complex, the energies of two charge-separated excited states of (1)nπ* and (1)ππ* character are connected to the energies of the locally excited (1)nπ* and (1)ππ* states of the pyridine chromophore via a low energy barrier. The charge-separated excited states are strongly stabilized by the transfer of a proton from water to pyridine. The energies of the resulting biradical states intersect the potential-energy surface of the closed-shell ground state as a function of the proton-transfer coordinate. The resulting radical pair may dissociate to yield pyridinium and hydroxyl radicals. The photochemistry of the hypervalent pyridinium radical has been explored with the same computational methods. It has been found that a low-lying dissociative (2)πσ* excited state exists in pyridinium, which can lead to the photodetachment of the hydrogen atom. Overall, the H2O molecule can thus be dissociated into H˙ and OH˙ radicals by the absorption of two ultraviolet photons. The relevance of these results for solar water splitting and solar carbon dioxide reduction is discussed.

Functional luminescent lanthanide complexes: Modulation of visible luminescence from europium complexes

The syntheses of three new ligands ( L 1 – 3 ), which are based upon a DO3A core and appended with additional receptor sites for metal cations, are described, together with their corresponding Eu(III) complexes ( Eu– L 1 – 3 ). The complexes are visibly luminescent in aqueous solution, following sensitization via the pyridine chromophore, showing characteristic narrow line-like emission from Eu(III). The luminescence properties show that water is effectively excluded from the inner coordination sphere of europium ( q = 0). Each of the complexes showed perturbed luminescence properties upon addition of a variety of d-block metal ions. For example, emission quenching was observed for each complex following addition of Cr(III) and Cu(II). Selectivity towards Hg(II) (over Cd(II), Cu(II) and Zn(II)) was demonstrated with Eu– L 3 , which possesses a receptor site incorporating a softer thiophene moiety. More specifically, Hg(II) binding resulted in changes in the form of the steady state emission spectrum, together with a corresponding reduction of the luminescence lifetime in water, which can be attributed to an increase in inner sphere hydration ( q = 2) and thus enhanced non-radiative deactivation of the 5D 0 state by proximate O–H oscillators.

Supramolecular photochirogenesis in sensitizing chiral nanopore: Enantiodifferentiating photoisomerization of (Z)-cyclooctene included and sensitized by POST-1

By using homochiral mesoporous POST-1 (Scheme 1) as an inherently chiral sensitizing host, supramolecular enantiodifferentiating photoisomerizations of (Z)-cyclooctene (1Z) were performed for the first time to examine the sensitizing ability of the chiral nanopores, walls of which are decorated with pyridine chromophore. The homochiral nanopores of POST-1 crystals were demonstrated to function as an effective chiral-sensitizing cavity to give the optically active (E)-isomer 1E in up to 5% enantiomeric excess (ee), thus expanding the scope of porous material-mediated chirogenesis to both ground and excited electronic states.

Luminescent Lanthanide Complexes with Stereocontrolled Tris(2-pyridylmethyl)amine Ligands: Chirality Effects on Lanthanide Complexation and Luminescence Properties

A series of tris(2-pyridylmethyl)amines including one and two asymmetric centers were synthesized in a stereo-controlled fashion as potential ligands of lanthanide cations. The reaction of chiral pyridylethyl methanesulfonates and bis(pyridylmethyl)amines occurred via an S(N)2 mechanism with complete inversion of asymmetric centers and gave the stereocontrolled tris(2-pyridylmethyl)amines, the stereochemical purity of which was ascertained by GPC, NMR, X-ray, and polarimetry experiments. They formed stable Tb(3+) and Eu(3+) complexes having 1:1, 1:2, and 1:3 stoichiometry (metal:ligand) in CH(3)CN solutions. NMR and UV titration experiments revealed that their complexation behaviors were rarely influenced by ligand chirality but significantly affected by the nature of the counteranion and the concentration ratio of metal to ligand. The Tb(3+) and Eu(3+) complexes with these tripodal ligands exhibited characteristic luminescence spectra upon excitation for pyridine chromophores (260 nm), the intensities of which were largely dependent on the ligand chirality. The meso isomer of the disubstituted tripods particularly exhibited the enhanced terbium luminescence ca. three times more than its diastereomer and un- and monosubstituted tripods. Direct excitation at the lanthanide center had similar chirality effects on the luminescence profiles, indicating that the stereochemistry of the employed ligand largely influenced the lanthanide emitting processes. Since the ligand chirality finely modified the local coordination environments around the lanthanide center, the use of stereocontrolled ligands is applicable in design of the luminescent lanthanide complexes.

An evanescent field driven mono-molecular layer photoswitch: coordination and release of metallated macrocycles.

Photoswitching of 'on' and 'off' coordination sites in a self assembled monolayer containing the 4-(arylazo)pyridine chromophore has been achieved using the evanescent field and illustrated through coordination and photon induced release of zinc tetraphenylporphyrin.

Intensity Behaviour of the Long Wavelength UV Transition of the Pyridine Chromophore Under Substitution in the Para Position to the Nitrogen Atom

When pyridine is para substituted to the nitrogen atom, the intensity of the long wavelength electronic transition is strongly decreased compared to the ortho and meta derivatives. N belonging to the ring, plays the part of a donating center when a strong electron withdrawing substituent is in the para position, and the part of an attracting center when faced to a donating substituent. the local transition moment vector of N, is in both cases opposed to the vector of the substituent. Furthermore, the π HOMO is priviledged (instead of the two highest π MO in benzene), and this HOMO does not allow a strong interaction with the substituent in the para position.

Intensity of the 250 nm Transition of the Pyridine Chromophore and of Some Methyl Derivatives

The intensity of the near UV transition of pyridine, pyrazine, and some of their methyl derivatives, is studied on the ground of the Interaction Vector Model (IVM), assuming that this transition is similar to the secondary one of the benzene chromophore.

The vacuum ultraviolet–circular dichroism spectrum of an isolated pyridine chromophore

The circular dichroism spectrum of (+)-5,6,7,8-tetrahydro-8,9,9-trimethyl-5,8-methanoquinoline, a molecule containing a pyridine chromophore perturbed by an alkyl moiety has been carried out down to 170 nm through the region of the allowed π→π* transitions.

Chiroptical properties of an isolated pyridine chromophore: the circular dichroism spectra in the near ultraviolet region of (–)-(R)-2-(1,2,2-trimethylpropyl)pyridine

The circular dichroism spectra of (–)-(R)-2-(1,2,2-trimethylpropyl)pyridine, under various conditions of solvent and temperature, are reported. The results are consistent with the presence of three electronic transitions (two n→π* and one π→π* excitations) in the spectral range examined (300–230 nm).

Induced optical activity in copolymers of (—)‐p‐(3‐menthyl) acrylate with 4‐vinylpyridine

AbstractThe present paper reports on the synthesis of copolymers of (—)‐p‐(3‐menthyl) acrylate (1) with 4‐vinylpyridine (2) by radical polymerization in a large range of composition. Reactivity ratio values of the two comonomers, evaluated by the Kelen‐Tüdös method, have allowed to show that 2 exhibits a rather high reactivity as compared with 1. The average sequence length of the co‐units and their distribution in the macromolecules were evaluated. The chiroptical properties of side chain pyridine chromophores were investigated by circular dichroism measurements and related to composition and distribution of the monomeric units.

ChemInform Abstract: THE OPTICAL ACTIVITY OF THE PYRIDINE CHROMOPHORE: MO ANALYSIS OF THE CIRCULAR DICHROISM SPECTRUM OF 5α‐CHOLEST‐2‐ENO(3,2‐B)PYRIDINE

Chemischer InformationsdienstVolume 11, Issue 26 Physical Organic Chemistry ChemInform Abstract: THE OPTICAL ACTIVITY OF THE PYRIDINE CHROMOPHORE: MO ANALYSIS OF THE CIRCULAR DICHROISM SPECTRUM OF 5α-CHOLEST-2-ENO(3,2-B)PYRIDINE S. GLADIALI, S. GLADIALISearch for more papers by this authorG. GOTTARELLI, G. GOTTARELLISearch for more papers by this authorB. SAMORI, B. SAMORISearch for more papers by this authorP. PALMIERI, P. PALMIERISearch for more papers by this author S. GLADIALI, S. GLADIALISearch for more papers by this authorG. GOTTARELLI, G. GOTTARELLISearch for more papers by this authorB. SAMORI, B. SAMORISearch for more papers by this authorP. PALMIERI, P. PALMIERISearch for more papers by this author First published: July 1, 1980 https://doi.org/10.1002/chin.198026045AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume11, Issue26July 1, 1980 RelatedInformation

The optical activity of the pyridine chromophore: MO analysis of the circular dichroism spectrum of 5α-cholest-2-eno[3,2-b]pyridine

5α-Cholest-2-eno[3,2-b]pyridine (III), a chiral molecule containing the pyridine chromophore, was synthesized, and its c.d. spectrum measured between 195 and 300 nm. An ab initio computation of the optical activity was carried out on 5,6,7,8-tetrahydroquinoline, which has P chirality, and which was considered as the most important fragment in determining the optical activity of (III). Good agreement was found between the calculated values and the experimental c.d. spectrum of (III) for all accessible transitions. The low energy n→π* is red-shifted relative to the first π→π* transition and no crossing of the two transitions occurs. No substantial contribution to the optical activity is given by the n→π* transition at higher energy. The contributions of a one-electron mechanism to the optical activity of the n→π* and first π→π* transitions are briefly discussed.

Circular dichroism of isomeric pyridylethanols

The room and low temperature absorption and c.d. spectra of the isomeric (–)-(S)-2-, 3-, and 4-pyridylethanols, (–)-(S)-(I)–(III) have been measured. The data obtained are satisfactorily interpreted by assuming the existence of a second n→π*(A2â†�A1) electronic transition of the pyridine chromophore at ca. 240 nm.

Ultraviolet absorption spectra of some 2-substituted pyridines. σ-π conjugation involving group IV elements

This study reports the electronic spectra, in cyclohexane and 95% ethanol solvents, of some members of several series of 2-substituted pyridines containing Group IV elements. The compounds all contain the Group IV elements separated by a saturated carbon atom from the pyridine chromophore. The positions and intensities of both the 1 L b and 1 L a pyridine bands are sensitive to the substituents. The results are interpreted in terms of carbon-metal (σ-π) hyperconjugation.