Photophysical properties and photoisomerization of aza derivatives of trans-2-styrylnaphthalene: trans-1-(2-pyrazinyl)-2-(n-quinoxalinyl)ethylene

A systematic study of the synthesis and properties of 1‐aza‐, 4‐aza‐, and 1,4‐diaza[4]helicenes as well as the previously unknown S‐shaped double 1,4‐diaza[4]helicenes has been reported. The synthetic route to the aza‐ and diaza[4]helicenes involved an electrophile‐induced cyclization of 3(2)‐alkynyl‐2(3)‐(naphthalen‐1‐yl)azines (i.e., quinoxaline, pyrazine, pyridine), which were prepared in two steps from the commercially available ortho‐dihalo‐substituted azine. Trifluoroacetic acid (TFA) and ICl were used as electrophiles. The ICl‐promoted cyclization provided the 5‐iodo derivatives of the aza‐ and diaza[4]helicenes in yields of 47–71 %. The use of TFA as the electrophile afforded the helicenes along with isomeric products from an alternative cyclization and subsequent 1,2‐shift of the C–C bond (e.g., naphtho[2,1‐f]quinoxalines or naphtho[2,1‐a]phenazines, 87–89 % total yield, 1.5–1.8:1 ratio). The presence of an iodine substituent in the hetero[4]helicenes allowed for the introduction of an alkynyl group by using a Sonogashira reaction. The subsequent cycloizomerization upon treatment with TFA gave the S‐shaped double 1,4‐diaza[4]helicenes. The molecular structures and crystal packing of the synthesized hetero[4]helicenes relative to those of [4]carbohelicene have been discussed.

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Synthesis and Characterization of Pyridine‐, Pyrazine‐, and Quinoxaline‐Derived [4]Helicenes and S‐Shaped Double [4]Helicenes

Gulevskaya

Shvydkova

Tonkoglazova

2018

Eur J Org Chem

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Fluorescence/photoisomerization competition in trans-aza-1,2-diarylethenes

et al. 2009

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The effect of the presence and position of the nitrogen heteroatom on the photobehaviour of a series of symmetric and asymmetric 1,2-diarylethenes, where one or both the one-, two- or three-membered aryl groups, linked to the ethene bridge, contain(s) nitrogen heteroatoms, has been investigated by fluorimetric and photochemical techniques. The yield of the radiative pathway is generally reduced with respect to the corresponding hydrocarbons, due to a smaller energy barrier for trans-->cis (E-->Z) photoisomerization in the singlet state, which often can be slightly favoured in the aza-compounds. All compounds investigated exist in solution as mixtures of two or more conformers, which can have different spectral and kinetic properties. Attempts to separate the intrinsic properties by selective photoexcitation, at a wavelength where the light is mainly absorbed by one conformer, allowed in some favourable cases the spectra and decay times of the largely prevalent (quasi-pure) conformer to be obtained. In two cases, the formation of intramolecular (hydrogen-bond-type) interactions between the nitrogen atom and the nearest hydrogen atom of the ethene bridge (proved by NMR measurements and confirmed by theoretical calculations) were found to stabilize a specific conformer thus affecting a selective relaxation of the excited molecule.

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Spectroscopic Investigation and Photophysics of a D-π-A-π-D Type Styryl Pyrazine Derivative

El‐Daly

Alamry

2015

J Fluoresc

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E,E-2,5-bis(3,4-dimethoxystyryl)pyrazine (BDSP)has been prepared by aldol condensation between 2,5-dimethypyrazine and 3,4-dimthoxybenzaldehyde and characterized by IR, 1HNMR, 13C NMR and X-ray crystallography.The electronic absorption and emission properties of BDSP were studied in different solvents. BDSP displays a strong solvatochromic effect of the emission spectrum that is reflected by large red shifts of its fluorescence emission maximum on increasing the solvent polarity, indicating a large change in dipole moment of BDSP upon excitation due to photoinduced intramolecular charge transfer (PICT). Excited state intermolecular hydrogen bonding affects the energy of emission spectrum and fluorescence quantum yield of BDSP dye. The dye solutions (1×10(-4) M) in DMSO, DMF, CH3CN and dioxane give laser emission in green region upon excitation by a 337.1 nm nitrogen pulse (λ=337 nm). The tuning range, gain coefficient (α), emission cross – section (σe) and half-life energy (E1/2) has been determined. Ground and electronic excited states geometric optimization were performed using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), respectively. A DFT natural bond analysis complemented the ICT. BDSP dye displays fluorescence quenching by colloidal silver nanoparticles(AgNPs). The fluorescence data reveal that radiative and non-radiative energy transfer play a major role in the fluorescence quenching mechanism.

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Photophysical properties and photoisomerization of aza derivatives of trans-2-styrylnaphthalene: trans-1-(2-pyrazinyl)-2-(n-quinoxalinyl)ethylene

Cited by 14 publications

References 35 publications

Synthesis and Characterization of Pyridine‐, Pyrazine‐, and Quinoxaline‐Derived [4]Helicenes and S‐Shaped Double [4]Helicenes

Synthesis and Characterization of Pyridine‐, Pyrazine‐, and Quinoxaline‐Derived [4]Helicenes and S‐Shaped Double [4]Helicenes

Fluorescence/photoisomerization competition in trans-aza-1,2-diarylethenes

Spectroscopic Investigation and Photophysics of a D-π-A-π-D Type Styryl Pyrazine Derivative

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