Mei-Jin Lin

Bay-substituted perylene bisimide dye with an undistorted planar scaffold and outstanding solid state fluorescence properties

Single crystal X-ray analysis reveals a flat perylene π-scaffold for a perylene bisimide bearing bulky 2,6-diphenylphenoxy substituents at the 1,7 bay positions. The flat structure provides sharp vibronic progressions in the absorption and fluorescence spectra, the sterical shielding outstanding fluorescence quantum yields in the solid state.

Structure–property relationships for 1,7-diphenoxy-perylene bisimides in solution and in the solid state

To elucidate the impact of widely employed solubilizing phenoxy substituents on the structural and functional properties of perylene bisimide (PBI) dyes a series of 1,7-diphenoxy-substituted PBIs was prepared from 1,7-dibromo PBI which exhibit hydrogen, methyl, isopropyl or phenyl substituents at one or both ortho positions of the phenoxy substituents. Despite increasing sterical congestion high yields of 74–88% could be obtained for all twofold aromatic nucleophilic substitution reactions. The structural and optical properties in solution and in the solid state were investigated by 1H NMR, UV-Vis absorption and fluorescence spectroscopy, single crystal X-ray analyses (four structures) as well as quantum chemical and force field calculations. For the latter we used an adapted force field which correctly reflects the rigidity of the PBI core. Our studies show that these dyes prefer to accommodate a slightly twisted molecular structure in solution that is supported by CH⋯O hydrogen bonds between the 1,7-oxygen and the 6,12-hydrogen substituents. Because of the rather shallow potential energy surface, however, the molecules may planarize in the crystalline state under the influence of packing forces as revealed by single crystal X-ray analyses for two derivatives bearing methyl or phenyl substituents at all phenoxy ortho-positions. Such substituents are also suited to enwrap the PBI π-scaffold and to prohibit PBI aggregation in the bulk state giving rise to defined vibronic progressions in the solid state UV-Vis absorption and emission spectra, and appreciable fluorescence quantum yields of up to 37%. In dichloromethane solution all of these 1,7-diphenoxy-substituted PBI dyes exhibit fluorescence quantum yields of 98–100% despite significant differences in the shape of the UV-Vis absorption band. The latter was explained in terms of rigidity because the molecules bearing four ortho-substituents at the phenoxy substituents were shown to prevail in much more fixed conformations compared to their more simple counterparts. Our findings underline that the conformational flexibility of bay-substituents can have an important impact on the functional properties of PBI dyes.

Molecular tectonics: modulation of size and shape of cuboid 3-D coordination networks

The pore size and shape of cuboid 3-D coordination networks may be modulated by combining rigid neutral organic tectons of different length bearing two pyridines oriented in a divergent fashion with zinc dication and SiF6 dianion behaving as a metallic node and as an inorganic tecton, respectively.

Perylene Bisimide Radicals and Biradicals: Synthesis and Molecular Properties

Unprecedented neutral perylene-3,4:9,10-tetracarboxylic acid bisimide (PBI) radicals and biradicals were synthesized by facile chemical oxidation of 4-hydroxyaryl-substituted PBIs. Subsequent characterization by optical and magnetic spectroscopic techniques, as well as quantum chemical calculations, revealed an open-shell singlet biradical ground state for the PBI biradical OS-2(..) (〈s(2)〉=1.2191) with a relatively small singlet-triplet energy gap of 0.041 eV and a large singlet biradical character of y=0.72.

Encapsulating Naphthalene in an Electron-Deficient MOF to Enhance Fluorescence for Organic Amines Sensing

Host-guest encapsulation of electron-rich naphthalene molecules into a weakly emissive porous metal-organic framework based on π-electron-deficient (π-acidic) naphthalene diimide tectons leads to orange-emissive crystals, which can be used to sense strongly basic organic amines in a fast response, high photostability, and tunable sensitivity. Moreover, such host-guest inclusion crystals are also a good photochromic probe for the detection of weakly basic N-methyl-2-pyrrolidone and N,N-dimethylformamide molecules.

Molecular tectonics: control of interpenetration in cuboid 3-D coordination networks

By imposing a two-fold interpenetration through the use of ZnSiF6 forming a linear pillar, combinations of rigid tectons bearing two divergently oriented pyridyl units interconnected either by a naphthyl or a biphenyl spacer with ZnSiF6 lead to stable porous crystalline materials.

Cooperative lone pair–π and coordination interactions in naphthalene diimide coordination networks

Lone pair–π interaction is an important but less studied binding force. Naphthalene diimides (NDIs) are ideal to form such an interaction because their quadrupole moment is exceptionally positive. Here, we report the combination of NDI ligands bearing two divergently oriented pyridyl units with different metal nitrates in different solvents resulting in six neutral 1-D coordination networks, in which the nitrate anions not only serve as capping ligands to coordinate to metal centers but also provide lone pairs to interconnect with the π-acidic NDI ligands through lone pair–π interactions. Interestingly, such lone pair–π interactions are found to have a synergic effect on the coordination interactions of the aforementioned NDI ligands with metal ions. In other words, metal-ion-directed self-assembly of NDI ligands is supposed to be driven by cooperative lone pair–π and coordination interactions.

The effect of protonation on the spectra and stabilities of alkoxyl substituted phthalocyaninatometals.

The protonation abilities of phthalocyaninatometals (MPcs) increase but their stabilities reduce by the introduction of alkoxyl substituents at alpha position. In the toluene, the order of mono-protonation rate for the tetra-alpha-(2, 2, 4-trimethyl-3-pentoxy)phthalocyaninatometals sorts with the center metals is Zn>Co>Cu>Ni>Fe, which is opposite to the order of their wavelength difference between the Q bands and X bands. However, their mono-protonated species can be decomposed easily at the rate order FePc>CoPc>CuPc>NiPc>ZnPc, analogous to their decomposition abilities in the benzoylperoxide (BPO) oxidation. In addition, it is interesting that a more remarkable decomposition is found when partial CuPc was mono-protonated.

From achiral tetrazolate-based tectons to chiral coordination networks: effects of substituents on the structures and NLO properties

Using a hydrothermal synthesis method, the combination of four tetrazolate-yl acylamide tectons bearing substituents of different sizes, 4-nitro-N-(1H-tetrazol-5-yl)benzamide (H-NTBAN), 4-fluoro-N-(1H-tetrazol-5-yl)benzamide (H-NTBAF), N-(1H-tetrazol-5-yl)isonicotinamide (H-NTINA) and N-(1H-tetrazol-5-yl)thiophene-2-carboxamide (H-NTTCA), with cadmium dichloride led to four crystalline coordination networks, named Cd3(NTBAN)6 (1), Cd(NTBAF)2 (2), Cd(NTINA)2 (3) and Cd(NTTCA)2 (4), respectively. The X-ray diffraction analysis revealed that compounds 2, 3 and 4 possess a 3D non-interpenetrated diamondoid framework, while compound 1 is of a 0D trinuclear structure. Wherein, compounds 2, 3 and 4 crystallized in chiral space groups with significant second harmonic generation (SHG) efficiencies. The effects of substituents in the semirigid tetrazole-yl acylamide tectons on the structural topologies as well as on the nonlinear optical properties of the generated coordination networks are discussed.

Coordination polymers of tetrazole-yl acylamide with octahedrally coordinated divalent transition metals: the effects of metal centers and side-groups on the structural topologies and symmetries

Hydrothermal reactions of divalent transition metal salts with two different-sized tetrazole-yl acylamide ligands, N-(1H-tetrazol-5-yl)acetamide (H-NTAA) and N-(1H-tetrazol-5-yl)propionamide (H-NTPA), led to six crystalline coordination polymers, named Cd(NTAA)2 (1), Zn(NTAA)2·∼H2O (2), Cu(NTAA)2 (3), Mn(NTAA)2 (4), Cd(NTPA)2 (5), Mn(NTPA)2 (6), respectively. The X-ray diffraction analysis revealed that compound 2 is a 1D zigzag chain, compounds 3 and 4 exhibit an interesting 2D 44-sql network, while compounds 1, 5 and 6 possess a 3D non-interpenetrated diamondoid framework. Wherein, compounds 1, 4, 5 and 6 crystallized in an acentric space group with significant second harmonic generation (SHG) efficiencies. The effect of metal ions and that of small aliphatic acyl side-groups in semirigid tetrazole-yl acylamide ligands on the structural topologies and symmetries of generated coordination polymers are discussed.