V. M. Lee

Reconfigurable molecular logic gate operating in polymer film

2-Styrylquinoline (2-SQ) comprises two functional active sites, ethylenic group and aza-function (endocyclic nitrogen atom), and can exist in four forms which are thermally stable, have different spectral properties, and are easily interconvertible. Due to these features, 2-SQ, embedded into a polymer film, can act as “AND”, “OR”, “INHIBIT”, “NAND”, “NOR” and “IMPLICATION” logic gates; it can also function as a 1 : 2 digital demultiplexer. The molecular logic gate utilizes two stimuli, irradiation by light and protonation, as inputs and absorbance as output. The gate can be easily reconfigured to various modes of operation by changing the initial state as well as the input and readout wavelength.

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.

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.

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.

Synthesis and spectral properties of Azahetero-aromatic derivatives of 2-styrylanthracene

Novel azaheteroaromatic derivatives of 2-styrylanthracene: 2-styrylbenzo[g]quinoline and 3-styryl- acridine were obtained from 3-nitro-2-naphthaldehyde and 2-bromo-4-methylbenzoic acid. Spectral properties of the new compounds were studied.

Proton-controlled photoisomerization of 1-(2-pyridyl)-2-(2-quinolyl)ethylene

Quantum-chemical calculations (B3LYP/6-31G*) predict the formation of intramolecular hydrogen bond (IMHB) in the monoprotonated Z-isomer of 1-(2-pyridyl)-2-(2-quinolyl)ethylene (2P2Q), with this bond stabilizing the isomer relative to its E-counterpart. An experimentally observed increase in the quantum yield of trans-cis photoisomerization (φtc) by more than an order of magnitude (from 0.033 to 0.42 in acetonitrile) on passing from the neutral to the monoprotonated form of 2P2Q can be associated with IMHB, which manifested itself in the spectral properties of the Z-isomer. The IMHB breaks in the diprotonated form, and the value of φtc decreases back to the initial value. In addition to the photoisomerization, the photoreduction and photoaddition reactions of solvent molecules have been observed in an ethanol solution of 2P2Q.

Spectral and photochemical properties of hydroxylated 2-styrylquinoline derivatives

The spectral and photochemical properties of 2-(4-hydroxystyryl)quinoline 1 and 2-(2-hydroxystyryl)quinoline 2 have been studied. The trans-cis photoisomerization quantum yield for 1 and 2 in the neutral form is 0.2–0.5, and it is reduced by a factor of 6–7 by protonation, presumably, owing to the competitive process of hydroxyl group deprotonation in the excited state and the formation of quinoid tautomers. The quantum yield of the back cis-trans photoisomerization in the protonated form varies insignificantly. The neutral, protonated, and deprotonated forms of 1 have been used for to simulate a molecular logic gate, the half-adder with chemical inputs and absorbance as outputs.

Adiabatic trans-cis photoisomerization and photocyclization of 8-styrylquinoline

Kinetics of the photocyclization of trans-8-styrylquinoline into 10a,10b-dihydronaphtho[1,2-h]quinoline (4-azachrysene) was studied in hexane. It was found that in addition to the expected two-step (two-quantum) route with trans-cis photoisomerization occurring in the first step with a quantum yield of φtc = 0.13 with consequent photocyclization of the cis-isomer with a quantum yield of 0.23. The direct singlequantum photocyclization of the trans-isomer with a quantum yield of 0.009 is also observed. The latter observation indicates that the excited trans-isomer isomerizes without loss of excitation to the excited cis-isomer, which then undergoes cyclization, i.e., the trans-cis photoisomerization proceeds partially by adiabatic mechanism t* → c*.