T. N. Gavrishova

Photoisomerization of 2-styrylquinoline in neutral and protonated forms

The quantum yields of the trans-cis and cis-trans photoisomerization of 2-styrylquinoline (2SQ) and its several derivatives were measured in neutral, protonated, and quaternized forms. It was shown that electron-donor substituents in the styryl moiety increase the quantum yield of trans-cis photoisometization ϕtc in the neutral form as a result of stabilization of the intermediate zwitterionic perpendicular conformer. On passing from the neutral to the positively charged forms (protonated or quaternized), an increase in the quantum yields to ϕtc > 0.5 was observed, thus suggesting in terms of the classical diabatic mechanism of photoisomerization via the perpendicular conformer the shift of the minimum on the potential energy surface (PES) of the S1 state relative to the maximum of the S0 state PES to the cis-isomer or a possible contribution of the adiabatic route to the photoisomerization of the 2SQ cations.

Experimental and quantum chemical investigation of photochemical properties of a covalently bound bis(styrylquinoline) dyad

Abstract1,3-Bis(4-(2-quinoline-2-vynyl)phenoxy)propane a bis(styrylquinoline) dyad (S3S), has been synthesized and investigated. A comparison of S3S with the model 2-(4-methoxystyryl)quinoline (MeOSQ) has shown that integration of two styrylquinoline fragments (SQ) into the covalently bound dyad affects neither spectral properties nor the initial rate of the transcis photoisomerization reaction, but it results in both a change of the photolysis kinetics in general and the enrichment of the photostationary state in the isomer that has had a higher molar absorption coefficient at the irradiation wavelength. The kinetic scheme of the dyad photolysis including four isomers and eight reactions has been analyzed. The photoisomerization quantum yield of the SQ moiety of the dyad is half that of MeOSQ. Density functional theory (DFT) B3LYP/6–31G* calculation has revealed that the styrylquinoline nuclei in both MeOSQ and the S3S dyad have close geometrical parameters and electron structure. Absorption spectra have been calculated by the TDDFT method in the isolated-molecule approximation for an intermolecular hydrogen bonding-stabilized cluster with the ethanol molecule and in terms of the polarized continuum model (PCM). The absorption spectrum of the trans (E)-isomer is represented as spectra of two s-conformers, and the TDDFT method for the cis (Z)-isomer underestimates the energy of the long-wavelength absorption band.

Microwave-assisted solvent-free synthesis of 2-styrylquinolines in the presence of zinc chloride

An efficient solvent-free procedure has been developed for the synthesis of (E)-2-styrylquinoline derivatives under microwave irradiation in the presence of zinc chloride. The developed procedure is advantageous due to shorter reaction time and simpler workup.

Design of fully photonic molecular logic gates based on the supramolecular bis-styrylquinoline dyad

The design algorithm of fully photonic two-address molecular logic gates (MLGs) based on the supramolecular bis-styrylquinoline S3S dyad was considered in which two pieces of 2-(4-oxystyryl)quinoline are linked to each other with a trimethylene “bridge.” The reaction of the photoisomerization of styrylquinoline fragments is used to switch between the states, and the reading of the output signal is done by the absorption and luminescence of these fragments. In the latter case, both input and output signals for MLGs are photons; i.e., homogeneity of input and output signals is achieved, which is necessary for the construction of more complex circuits from these gates. It is shown that the S3S dyad simulates the action of logic gates “AND,” “OR,” “NOT-AND” (“NAND”), “NOT-OR” (“NOR”), “IMPLICATION” (“IMP”), and “INHIBIT” (“INH”).

Spectral-Luminescent properties of the dioxytetramethylene-bridged naphthol-styrylquinoline dyad

The spectral-luminescent properties of the naphthol-styrylquinoline dyad 2-(E)-{4-[4-(3-hydroxynaphthalen-2-yloxybutoxy]styryl}quinoline (SQ4Np) have been investigated. Fluorescence quenching of the naphthol (Np) moiety via energy transfer to the styrylquinoline (SQ) moiety has been observed upon dyad excitation. A comparison of stationary and time-resolved fluorescent spectroscopy data has revealed two groups of conformers, for which the energy-transfer rate constants differ by more than two orders of magnitude. According to quantum-chemical calculations (B3LYP/6-31G* method), the s-cis-conformation of the SQ fragment is the most stable SQ4Np conformer with the all-trans-conformation of the dioxytetramethylene bridge and intramolecular hydrogen bond in the Np moiety; the van der Waals size of this conformer is 2.90 nm, which is less than the calculated Forster radius of R0 = 3.8 nm.

The effect of substituents in the styryl moiety on the photocyclization of 4-styrylquinoline derivatives

The reaction of photocyclization and oxidation of 4-styrylquinoline and its derivatives with substituents in the p-position of the styryl moiety to the corresponding derivatives of benzo[i]phenantridine has been studied. It has been found that electron-donating substituents reduce the quantum yield of photocyclization under steady-state photolysis. Quantum-chemical calculations of the enthalpy of the cyclization reaction and analysis of the structure of the frontier molecular orbitals in the cis-isomer led to the conclusion that the observed effects relate to the influence of the substituents on both the photocyclization reaction proper and the thermal stability of dihydrobenzo[i]phenantridine derivatives as the primary products of photocyclization.

Reactions of intramolecular C-N photocyclization and photoaddition to the double bond of methoxy- and methoxycarbonyl-substituted styrylbenzoquinolines

Photochemical reactions of C-N photocyclization and ethanol photoaddition, which are side reactions relative to photoisomerization, have been studied for 3-(3-methoxystyryl)benzo[f]quinoline (3MSBQ) and 3-(4-methoxycarbonylstyryl)benzo[f]quinoline (4MCSBQ). The overall quantum yield of the side reactions is almost two orders of magnitude below that of photoisomerization. The presence of several photoproducts has been revealed by principal component analysis. By electrospray mass spectrometry and absorption and emission electron spectroscopy, it has been found that the photoproducts are 12b-azoniabenzo[c]chrysene derivatives formed via the intramolecular C-N photocyclization and adducts with ethanol, of which the former dominate for 3MSBQ and the latter are prevalent for 4MCSBQ. The relative stability of the primary photocyclization products for a series of styrylbenzoquinolines calculated by the DFT (B3LYP/6-31G*) method correlates qualitatively with experimental data on the formation of the final oxidized condensed products.

Spectral and luminescent properties and photoisomerization of substituted styrylbenzoquinolines

The spectral, luminescent, and photochemical properties of 3-styrylbenzo[f]quinoline (3SBQ) derivatives containing methoxy and methoxycarbonyl groups have been studied. All of these compounds luminesce in the region of 380–480 nm with quantum yields up to 0.74 and undergo reversible photoisomerization with quantum yields of 0.2–0.5. It has been found that compounds with a methoxy group at the meta-position and a methoxycarbonyl group at the para-position of the styryl moiety are unstable photochromes and also undergo other photochemical reactions side relative to photoisomerization. The absorption spectra of the two 3SBQ s-conformers calculated by the density functional theory (DFT) method (TD-B3LYP/6-31G*) describe well the experimental spectrum. The analysis of the structures of molecular orbitals and transitions between them has made it possible to explain the observed effects of substituents on the absorption spectrum of 3SBQ.

Photoisomerization of naphthylquinolylethylenes in neutral and protonated forms

The quantum yield of the trans-cis photoisomerization of 1-(1-naphthyl)-2-(2-quinolyl)ethylene and 1-(2-naphthyl)-2-(2-quinolyl)ethylene is close to the theoretical limit (0.5) for diabatic photoisomerization and does not change on passing from the neutral to the protonated form. The data obtained indicate the absence of the α-effect for the test compounds, which consists in an increase in the trans-cis photoisomerization quantum yield to values of >0.5 upon protonation of some azadiarylethylenes with the nitrogen atom in the α-position to the ethylene group.

Spectral and photochemical properties of bis(styrylquinoline) dyad with o-xylylene bridge

Properties of 1,2-bis-(4-[(E)-2-quinoline-2-vinyl)phenoxymethyl)benzene, a bis(styrylquinoline) dyad SoS, in which two styrylquinoline fragments (SQ) are linked by o-xylylene bridge, have been investigated. Photoisomerization of the SQ fragment in the bichromophoric dyad occurs as efficiently as in the monochromophoric model compound 2-(4-methoxystyryl)quinoline MeSQ. Along with photoisomerization, [2 + 2]-photocycloaddition occurs affording tetrasubstituted cyclobutane. According to the quantumchemical DFT calculations, this reaction is assisted by preorganizing action of o-xylylene group orienting the two SQ fragments in the dyad in the head-to-head position.