Jiben Meng

Synthesis of functionalized spiropyran and spirooxazine derivatives and their photochromic properties

Abstract Three series of functionalized spiropyrans and spirooxazines derivatives were synthesized and their photochromic properties were investigated in particular regard to the fatigue resistance, the lifetime of the colored merocyanine form and the interaction of the colored form molecule. (1) Spiropyrans 5 and spironaphthooxazines 6 having an antioxidant group as a pendant exhibited higher fatigue resistance than that of the parent spiro compounds in solution. In particular, spiropyrans 5 showed higher resistance than parent compound 1 in the presence of an equimolar amount of the corresponding antioxidant. (2) bis-Spironaphthooxazines 8a–8i and 10 connected through a phosphoryl group exhibited higher fatigue resistance and longer lifetime of the colored merocyanine form than those of the parent spirooxazine 7. (3) Symmetrical bis-spiro photochromic compounds 15 and 16 and unsymmetrical bis-spiro compounds 13, 14 and 17 were synthesized. The bis-spiro photochromic compounds were found to undergo intramolecular interaction between the colored merocyanine forms.

Synthesis and liquid crystal properties of a new class of calamitic mesogens based on substituted 2,5‐diaryl‐1,3,4‐thiadiazole derivatives with wide mesomorphic temperature ranges

Liquid crystals based on substituted 2,5‐diaryl‐1,3,4‐thiadiazole derivatives (1a–1f, 3a and 3b) and 1,3,4‐oxadiazole analogues (2a–2f, 4a and 4b) were synthesised and characterised by 1H, 13C nuclear magnetic resonance, Fourier transform infrared, mass spectrometry, high‐resolution mass spectrometry techniques and elemental analyses. The X‐ray crystal structure of 1e revealed that it contains tilted lamellar arrangement of molecules in the crystalline solid. The liquid crystal properties have been investigated by polarised‐light optical microscopy, differential scanning calorimetry and in‐situ variable‐temperature X‐ray diffraction. All compounds (except 2e and 2f) exhibited thermotropic liquid crystal behaviours with various mesophases (smectic A and C, nematic N or soft crystal E phases). Notably, the 1,3,4‐thiadiazole derivatives consistently have wider mesomorphic temperature ranges than those of the respective 1,3,4‐oxadiazole analogues. The solutions of all compounds in CH2Cl2 individually displayed one or two absorption bands with λ max values at 297–355 nm and emitted with λ max values at 363–545 nm and quantum yields of 0.12–0.73. Structure–property relationships of these compounds are discussed in the contexts of their molecular structures and weak intermolecular interactions.

Synthesis and mesomorphic behaviour of heterocycle‐based liquid crystals containing 1,3,4‐oxadiazole/thiadiazole and thiophene units

A new class of thiophene‐based 1,3,4‐oxadiazole derivatives ( n ‐OXD‐R) and the corresponding 1,3,4‐thiadiazole derivatives ( n ‐THD‐R) was synthesised and characterised by means of 1H NMR, 13C NMR, MS and HRMS techniques. Liquid crystal properties were investigated by differential scanning calorimetry, polarising optical microscopy and variable temperature X‐ray diffraction measurements. All the 1,3,4‐thiadiazole compounds ( n ‐THD‐R) exhibited enantiotropic mesophases (smectic A, smectic C and nematic phases) with wide mesomorphic temperature ranges (68.5–109.5°C). In contrast, only the oxadiazole compounds 8‐OXD‐Cl, 9‐OXD‐Cl and 10‐OXD‐Cl, bearing electron‐withdrawing terminal group and longer alkoxy chain, displayed an enantiotropic smectic A phase with narrow mesomorphic temperature ranges (4.1–10.9°C). The effects of central heterocyclic rings, the terminal groups and the length of the terminal alkoxy on the mesomorphic behaviour are discussed.

Stereo and regioselective synthesis of (Z)-β-arylseleno-α,β-unsaturated ketones via selenocarbonylation addition of arylselenoesters to alkynes catalyzed by copper(I)

Abstract Selenocarbonylation addition reaction of selenoesters to nonactived terminal alkynes under the catalysis of CuX produces (Z)-β-arylseleno-α,β-unsaturated ketones in high selectivity and high yields. The mechanism of this reaction is also discussed.

Synthesis, single crystal structure and liquid crystalline properties of bent-shaped 2,5-diaryl 1,3,4-oxadiazoles

Two bent-shaped 1,3,4-oxadiazole-based compounds, namely 2-[4-(2-(4-methylphenyl)-(E)-1-ethenyl)]phenyl-5-(4-pentyloxyphenyl)-1,3,4-oxadiazole 5a and 2-[4-(2-(4-fluorophenyl)-(E)- ethenyl-5-(4-pentyloxyphenyl)-1,3,4-oxadiazole 5b, were synthesised and their liquid crystalline properties were studied in this paper. Compound 5a exhibited an enantiotropic nematic mesophase, while 5b displayed an enantiotropic smectic A phase. No banana-shaped mesophases were found in these mesogens, although they adopt a bent-shaped molecular structure as confirmed by the single X-ray diffraction crystallography.

Synthesis and liquid crystalline properties of substituted 2,5-diaryl 1,3,4-oxadiazole derivatives without flexible chains

A series of new compounds based on aromatically 2,5‐disubstituted 1,3,4‐oxadiazoles without flexible chains, formulated as p‐R–C6H4–(OC2N2)–(p‐C6H4)2–R′ with (i) R = CH3O, R′ = CH3O, CH3S, F, H (Ia–Id), (ii) R = CH3S, R′ = CH3O, CH3S, F, H (IIa–IId) and (iii) R = F, R′ = CH3O, CH3S, F, H (IIIa–IIId) (p‐C6H4 and OC2N2 represent a p‐phenylene spacer and a 1,3,4‐oxadiazole ring, respectively), were synthesised and characterised by 1H and 13C NMR, MS and HRMS techniques. Mesomorphic properties were investigated using differential scanning calorimetry and polarizing optical microscopy. All of the target compounds (except Id, IId, IIIc and IIId) exhibited an enantiotropic nematic mesophase with high melting temperatures. The liquid crystalline properties of these compounds were influenced greatly by polarity, steric factors and positions of the terminal groups. The effect of the terminal groups on the liquid crystal properties is discussed.

An unexpected participation of oxygen in a novel synthesis of [2,2'-bi-1H-indene]-3,3'-dialkyl-3,3'-dihydroxy-1,1'-diones

Abstract This paper describes, for the first time, a short synthetic procedure for [2,2′-bi-1H-indene]-3,3′-dialkyl-3,3′-dihydroxy-1,1′-diones ( 1a–f ). The key feature of this synthetic method lies in the participation of oxygen when the intermediate arises from the nucleophilic addition of alkylmagnesium bromide to 2,2′-biindanylidene-1,1′,3,3′-tetraone. The background leading to the development of this synthesis is discussed, together with the proposal of a novel reaction mechanism. The structures of all the new compounds have been determined by X-ray crystallography.

Synthesis and comparative study of the heterocyclic rings on liquid crystalline properties of 2,5-aryl-1,3,4-oxa(thia)diazole derivatives containing furan and thiophene units

A series of heterocyclic liquid crystalline compounds containing 1,3,4-oxadiazole/thiadiazole, furan and thiophene units were synthesised and characterised by means of electrospray ionisation-mass spectrometry (ESI-MS), high-resolution mass spectroscopy (HRMS), 1H nuclear magnetic resonance (NMR) and 13C NMR. The thermal behaviours were investigated by differential scanning calorimetry (DSC) and polarised optical microscopy (POM). The effect of the 1,3,4-oxadiazole, 1,3,4-thiadiazole, furan, thiophene and benzene rings on the liquid crystalline properties was discussed briefly in context with the geometrical and electronic factors. The results showed that the tendency to form mesophases follows the sequence: 1,4-disustituted benzene >2,5-disubstituted thiophene >2,5-disustituted furan and 1,3,4-thiadiazole >1,3,4-oxadiazole.

A multistep photoreaction of aromatic aldehydes with heteroaromatics in the solid state

Abstract Mixed crystals, prepared by resolidification of the melt of a mixture of 5-formyl-1,3-dimethyluracil (1a) and antipyrine (7) crystals (molar ratio, 1:2.5), and irradiated with a high-pressure mercury lamp under nitrogen, gave a photocondensation product 8a, as in the previously reported solid state photoreaction between 1a and indole. Similarly, irradiation of mixed crystals of substituted benzaldehydes and indole gave the corresponding photocondensation product 3. A mechanism involving an oxetane intermediate 4 was proposed for the formation of 3. The nature of the starting mixed crystals was examined by powder X-ray diffractometry.

Intermolecular interactions in the formation of two-component molecular crystals composed of chloronitrobenzoic acids and 4-benzoylpyridine

Abstract The molecular structures of six two-component molecular crystals using chloronitrobenzoic acids and 4-benzoylpyridine as components were characterized by a combination of techniques: solution NMR, solid-state IR spectra, differential scanning calorimetry (DSC) and single-crystal X-ray crystallography. The X-ray analysis revealed that the brief alternation of substituents in acid components greatly affected the packing modes of molecular crystals, and that the weaker intermolecular interactions such as C–H⋯O hydrogen bondings and π–π stacking interactions play a significant role in determining the packing modes of molecular crystals.