V. M. Li

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.

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”).

Multifunctional Photonic Molecular Logic Gate Based On A Biphotochromic Dyad With Reduced Energy Transfer.

Using molecular logic gates (MLGs) for information processing attracts attention due to perspectives of creating molecular computers. Biphotochromic dyads are suitable models of photonic MLGs. However, they suffer from one weakness: the activity of one of the photochromes is often quenched because of Förster resonance energy transfer (FRET). Herein, we designed a dyad with reduced FRET, in which both photochromes keep their photoactivity thanks to spectral and spatial separation, allowing MLG switching between different states. This novel dyad reproduces the functionality of the full set of 16 two-input gates, as well a reversible gate-dual inverter, all gates are photonic.

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.

Spectral and photochemical properties of isomeric styrylbenzoquinolines

Photochemical properties of the annelated 2-styrylquinoline (2SQ) derivatives 2-styryl-benzo[g]quinoline (2SBQ) and 3-styrylbenzo[f]quinoline (3SBQ) and 3-styrylacridine (3SA) have been investigated by experimental and quantum-chemical methods. It has been found that the trans-isomer of 3SBQ undergoes the photoisomerization reaction with a quantum yield of φtc= 0.19, which increases to 0.44 for the protonated form, with the fluorescence quantum yield decreasing from 0.74 to 0.09. In contrast, the trans-isomers of 2SBQ and 3SA are photochemically inert in both neutral and protonated forms, φtc < 10−3. Quantum-chemical calculation by the PM3 method show that the difference in photochemical properties of 2SBQ and 3SBQ is due to the difference in the structure of frontier molecular orbitals, which, in turn, results in the difference of the shape of the potential energy surface of excited S1 states. Comparison of the properties of 2SBQ and 3SBQ with those of 2SQ reveals size and topological effects in the photochemistry of aza-diarylethylenes.

Synthesis of di- and triazido derivatives of 2,4,6-triphenylpyridine

The possibility of obtaining new di- and triazidophenylpyridines: 4-phenyl-2,6-bis(4-azidophenyl) pyridine and 2,4,6-tris(4–azidophenyl)pyridine by a three-stage synthesis from commercially available compounds was studied.

Synthesis and luminescent characteristics of 3- and 4-hydroxy-, carboxy-, methoxy-, and methoxycarbonylstyrylbenzo[f]quinolines

A convenient one-stage method was applied to the preparation of trans-isomers of 3- and 4- hydroxy-, carboxy-, methoxy-, and methoxycarbonylstyrylbenzo[f]quinolines, and the luminescent characteristics of obtained compounds were examined. The quantum yield values of fluorescence of the obtained styrylbenzo[f]quinolines depend on the position and the nature of the substituent and vary in the range 0.03–0.74.

Spectral and photochemical properties of styrylquinoline-merocyanine dyads based on 2-styrylquinoline

The properties of styrylquinoline-merocyanine dyads, in which the styrylquinoline (SQ) and merocyanine (MC) moieties are linked with a bridge of three (SQ3MC dyad) and eleven (SQ11MC dyad) methylene groups, have been compared with the properties of the model compounds 2-(4-methoxystyryl)quinoline and 1-ethyl-2-(4-methoxystyryl)quinolinium perchlorate, of which the latter is the O-methylated merocyanine derivative. Efficient inductive-resonance energy transfer (FRET) from the SQ to the MC moiety has been revealed, resulting in the quenching of the former and sensitization of the latter. The quenching of the SQ moiety manifests itself in a decrease in the quantum yield of trans-cis photoisomerization and fluorescence, and the sensitization of the MC moiety enhances these parameters. The efficiency of energy transfer decreases from 96 to 87% on passing from the SQ3MC to SQ11MC dyad.