Yu-Xin Peng

Asymmetrical/Symmetrical D−π–A/D−π–D Thiazole-Containing Aromatic Heterocyclic Fluorescent Compounds Having the Same Triphenylamino Chromophores

A family of linear asymmetrical D-π-A and symmetrical D-π-D types of thiazole-based aromatic heterocyclic fluorescent compounds bearing various electron-donating and electron-withdrawing tails (bromo, triphenylamino, pyridyl, thienyl and benzoic acid) have been designed and prepared successfully. Synthetic, structural, thermal, spectral and computational comparisons have been carried out for related compounds because of their adjustable electronic properties. It is interesting to mention that compound 2 can be prepared from 5-bromothiazole by one-pot Suzuki-Miyaura coupling and subsequent C-H activation reactions via a 5-TPA-substituted thiazole intermediate 1. X-ray single-crystal structures of six compounds indicate that they all crystallize in the triclinic P1 space group and the thiazole core exhibits different dihedral angles with its adjacent benzene ring of the triphenylamino group (3.6(3)-40.8(3)°). The photophysical and electrochemical results demonstrate that compound 7 exhibits high electrochemical activity with a green fluorescence emission. Meanwhile, compounds 1, 2, and 6 show high luminescence quantum yields, and compound 8 exhibits excellent thermal stability (T(d(10)) = 503 °C).

Coplanar bithiazole-centered heterocyclic aromatic fluorescent compounds having different donor/acceptor terminal groups.

A family of stable and soluble bithiazole-centered heterocyclic aromatic fluorescent compounds is described herein. All these multiple N-donor containing compounds have effective π-conjugated systems and different imidazole, pyridine, thiophene, triphenylamino, benzoic acid, and ethyl benzoate tails showing distinguishable D-A-A-D and A-A-A-A structures. X-ray single-crystal structures of seven compounds indicate that all of the bithiazole cores have the same trans coplanar configuration but exhibit different dihedral angles with their adjacent aromatic heterocycles (4.5(6)-69.7(3)°). Optical and electrochemical results demonstrate that the TPA-terminated bithiazole compound 2TPA2TZ has yellow fluorescence and reversible redox activity as well as extraordinarily high thermal stability. Theoretical and experimental studies have been made to reveal the differences from related compounds with adjustable electronic properties. The internal reorganization energy (λ) studies have been carried out to indicate the differences between the bithiazole-based derivatives and the corresponding bithiophene-based counterparts.

Advantage of the N-Alkylation Strategy for Retaining the Molecular Planarity for Oligothiophene/Imidazole/1,10-Phenanthroline-Based Heterocyclic Semiconducting and Fluorescent Compounds

A family of planar oligothiophene/imidazole/1,10-phenanthroline (OTIP)-based heterocyclic, aromatic, semiconducting, and fluorescent compounds with N-substituted alkyl chains (allyl, n-butyl, n-octyl, n-dodecyl, and n-cetyl) have been designed and synthesized. They all have specific N-coordination sites, various donor-acceptor spacers, good molecular planarity, suitable solubility, and high thermal stability. In comparison with conventional double β-alkylation of the thiophene ring, our results reveal that the single imidazole N-alkylation strategy for OTIPs has the advantage of maintaining the planarity of the whole molecule, in addition to improving the solubility, which can be clearly verified by the small dihedral angles between adjacent thiophene/imidazole/1,10-phenanthroline (TIP) rings in eight X-ray single-crystal structures. In particular, n-dodecyl- and n-cetyl-substituted OTIPs (7 and 8) with the same molecular length of 2.37 nm (MW =939 and 1052), show good molecular planarity with the aforementioned dihedral angles of 8.9(5) and 10.4(5)°. Furthermore, special attention has been paid to the physicochemical properties of seven symmetrical OTIPs (6-8, 13-15, and 19), including two to six thiophene rings in the middle of their molecular structures. To the best of our knowledge, this is the first synthetic, structural, and spectral investigation into the N-alkylation of OTIP-based compounds.

Comparative structural and spectral analyses for mononuclear and dinuclear metal complexes of 2-thiophen and 2-(5-bromothiophen) imidazo[4,5-f][1,10]phenanthroline

A series of mononuclear and dinuclear mercury(I), mercury(II), nickel(II), lanthanum(III), ferrous(II) and ruthenium(II) complexes 4–11 with different metal/ligand molar ratios (1 : 1, 1 : 2 and 1 : 3), having 2-thiophenimidazo[4,5-f[[1,10[phenanthroline (TIP) and 2-(5-bromothiophen)imidazo[4,5-f][1,10[phenanthroline (5-Br-TIP) ligands, have been synthesized and structurally compared. In addition, three protonated salts of TIP and 5-Br-TIP (1–3) with PF6− and ClO4− counterions have been described herein where the proton is found to be located at one of the nitrogen atoms of 1,10-phenanthroline moiety. It is notable that the whole molecules of dinuclear mercury(I) and nickel(II) complexes 6 and 7 exhibit excellent planarity in the lengths of 2.52 and 2.90 nm, respectively. UV-Vis, 1H NMR and luminescence spectra of ligands TIP and 5-Br-TIP, protonated salts 1–3 and metal complexes 4–11 have also been studied and compared.

Visualized acid–base discoloration and optoelectronic investigations of azines and azomethines having double 4-[N,N-di(4-methoxyphenyl)amino]phenyl terminals

Two small molecular chromogenic sensors (azine MS-1 and azomethine MS-2) were synthesized for acid–base discoloration and optoelectronic investigations. It was found that the color of both sensors in solution and in the solid state changed obviously from yellow to purple and blue after treatment with acid, which could be easily detected by the naked eye. Furthermore, single-crystal conductance of MS-1 and MS-2 could be significantly enhanced after treatment with HCl gas flow. On the other hand, MS-2 showed relatively good film-forming ability and could be used as a hole transport material (HTM) in perovskite solar cells, exhibiting a power conversion efficiency (PCE) of 6.68%. To the best of our knowledge, this is the first demonstration of perovskite solar cells including a HTM based on a low-cost Schiff-base.

Simultaneous enhancement of fluorescence and solubility by N-alkylation and functionalization of 2-(2-thienyl)imidazo[4,5-f][1,10]-phenanthroline with heterocyclic bridges

A family of 2-(2-thienyl)imidazo[4,5-f][1,10]-phenanthroline (TIP) based compounds with large delocalized π systems has been designed and synthesized following the strategy of introducing alkyl chains and extending different S-, N- and O-containing aromatic heterocyclic tails. Simultaneous enhancements of the fluorescence emission and solubility in organic solvents for the resultant aromatic heterocyclic compounds 1–13 have been achieved. Analyses on twelve X-ray single-crystal structures indicate that the thiophene ring of the TIP unit in this series of compounds shows the same trans configuration with its imidazo[4,5-f][1,10]-phenanthroline core but different dihedral angles with the adjacent aromatic heterocycles. Thermal gravimetric analyses for ten imidazole N-substituted TIP derivatives reveal that they still retain good thermal stability with decomposition temperatures higher than 300 °C originating from their common TIP core, even with the introduction of the n-butyl radical in their molecular structure. Moreover, TPA and carbazole substituted compounds 2 and 9 were used as the ancillary ligands to prepare their corresponding ruthenium(II) sensitizers, BM3 and BM4, and their dye-sensitized solar cell performance was evaluated.

Three trinuclear copper(II) complexes bridged by μ 3- with different coordination modes

Three trinuclear copper(II) complexes bearing the same μ 3- bridge and triangular geometry, {[Cu3(bpy)6(CO3)](ClO4)4(CH3OH)(H2O)2} (1), {[Cu3(bpy)6(CO3)](ClO4)4(C2H5OH)4(H2O)2} (2), and {[Cu3(bpy)6(CO3)](PF6)4(H2O)2} (3) (bpy = 2,2′-bipyridine), have been synthesized and structurally characterized. The common [Cu3(bpy)6(CO3)]4+ cationic unit is found in 1–3 but distinguishable coordination is observed for the central bridge, namely μ 3-η 2, η 2, η 2 in 1, μ 3-η 1, η 1, η 1 in 2, and μ 3-η 1, η 1, η 2 in 3. Five-coordinate trigonal bipyramidal and square pyramidal as well as six-coordinate octahedral structures for the copper(II) centers in 1–3 are observed. The presence of different counterions and solvent is responsible for the variations of coordination spheres of copper(II) and crystal packing modes in 1–3.

Syntheses, characterizations of copper compounds containing a series of S-, N-containing aromatic heterocyclic 2,2′:6′,2″-terpyridine derivatives

Abstract A series of 2,2′:6′,2″-terpyridine (TPY) based aromatic heterocyclic compounds, extended by thiophene, 4-dibenzothiophene, and thiazole units at the para position of the central pyridine ring in TPY, are described in this paper. A new compound, 4′-(4′-dibenbenzothiophene-5-thiophene-2-yl)-2,2′:6′,2″-terpyridine (La), serves as a tridentate ligand to react with Cu(NO3)2·3H2O and CuCl2·2H2O, respectively, to produce two different Cu(II) complexes [Cu(La)2](NO3)2 and [CuLaCl2] with 1 : 2 and 1 : 1 metal/ligand ratios. Dibenzothiophene is first introduced to TPY via the thiophene bridge. The alterations in cis and trans configuration, dihedral angles between adjacent aromatic rings, and photophysical properties have been observed before and after Cu(II) complexation, which has been verified by their crystal structures, UV–vis and fluorescence spectra.