Carlos

A combined experimental and theoretical study of the two-photon absorption (2PA) properties of a series of quadrupolar molecules possessing a highly electron-rich heterocyclic core, pyrrolo[3,2-b]pyrrole, is presented. In agreement with quantum-chemical calculations, large 2PA cross-section values, σ_2PA≈10²–10³ GM (1 GM=10⁵⁰ cm⁴ s photon⁻¹), are observed at wavelengths of 650–700 nm, which correspond to the two-photon allowed but one-photon forbidden transitions. The calculations also predict that increased planarity of this molecule through removal of two N-substituents leads to further increase in the σ_2PA values. Surprisingly, the most quadrupolar pyrrolo[3,2-b]pyrrole derivative, containing two 4-nitrophenyl substituents at positions 2 and 5, demonstrates a very strong solvatofluorochromic effect, with a fluorescence quantum yield as high as 0.96 in cyclohexane, whereas the fluorescence vanishes in DMSO.

Nitro can shine: The strongly electron-donating character of pyrrolo[3,2-b]pyrroles, combined with the quadrupolar nature of derivatives, makes it possible to maximize two-photon absorption (S₀-S₃ or S₀-S₅ transitions) at λ≤700 nm, while maintaining reasonable values of cross-section. Unprecedented solvatofluorochromism of the 2,5-bis(4-nitrophenyl) derivative has no parallel among known dyes (see figure).

A detailed study on the effects of core halogenation of tetraazaperopyrene (TAPP) derivatives is presented. Its impact on the solid structure, as well as the photophysical and electrochemical properties, has been probed by the means of X-ray crystallography, UV/Vis and fluorescence spectroscopy, high-resolution electron energy loss spectroscopy (HREELS), cyclic voltammetry (CV), and DFT modeling. The aim was to assess the potential of this approach as a construction principle for organic electron-conducting materials of the type studied in this work. Although halogenation leads to a stabilization of the LUMOs compared to the unsubstituted parent compound, the nature of the halide barely affects the LUMO energy while strongly influencing the HOMO energies. In terms of band-gap engineering, it was demonstrated that the HOMO–LUMO gap is decreased by substitution of the TAPP core with halides, the effect being found to be most pronounced for the iodinated derivative. The performance of the recently reported core-fluorinated and core-iodinated TAPP derivatives in organic thin-film transistors (TFTs) was investigated on both a glass substrate, as well as on a flexible plastic substrate (PEN). Field-effect mobilities of up to 0.17 cm² Vs⁻¹ and on/off current ratio of >10⁶ were established.

A detailed study on the effects of core halogenation of tetraazaperopyrene (TAPP) derivatives is presented. Its impact on the solid structure, as well as the photophysical and electrochemical properties, has been probed by the means of X-ray crystallography, UV/Vis and fluorescence spectroscopy, high-resolution electron energy loss spectroscopy, cyclic voltammetry, and DFT modeling (see scheme).

Highly luminescent, photostable, and soluble lanthanide pentafluorobenzoates have been synthesized and thoroughly characterized, with a focus on Eu^III and Tb^III complexes as visible emitters and Nd^III, Er^III, and Yb^III complexes as infrared emitters. Investigation of the crystal structures of the complexes in powder form and as single crystals by using X-ray diffraction revealed five different structural types, including monomeric, dimeric, and polymeric. The local structure in different solutions was studied by using X-ray absorption spectroscopy. The photoluminescence quantum yields (PLQYs) of terbium and europium complexes were 39 and 15 %, respectively; the latter value was increased almost twice by using the heterometallic complex [Tb_0.5Eu_0.5(pfb)₃(H₂O)] (Hpfb=pentafluorobenzoic acid). Due to the effectively utilized sensitization strategy (pfb)⁻TbEu, a pure europium luminescence with a PLQY of 29 % was achieved.

Luminescent lanthanides: A series of highly luminescent, photostable, and soluble lanthanide pentafluorobenzoates have been synthesized and characterized, with a special focus on Eu^III and Tb^III complexes as visible emitters and Nd^III, Er^III, and Yb^III complexes as IR emitters (see figure). Powder and single-crystal X-ray diffraction data showed five different structural types, including monomeric, dimeric, and polymeric.

We present a nitrogen-containing polycyclic aromatic hydrocarbon (N-PAH), namely 12-methoxy-9-(4-methoxyphenyl)-5,8-diphenyl-4-(pyridin-4-yl)pyreno[1,10,9-h,i,j]isoquinoline (c-TPE-ON), which exhibits high quantum-yield emission both in solution (blue) and in the solid state (yellow). This molecule was unexpectedly obtained by a three-fold, highly regioselective photocyclodehydrogenation of a tetraphenylethylene-derived AIEgen. Based on manifold approaches involving UV/Vis, photoluminescence, and NMR spectroscopy as well as HRMS, we propose a reasonable mechanism for the formation of the disk-like N-PAH that is supported by density functional theory calculations. In contrast to most PAHs that are commonly used, our system does not suffer from entire fluorescence quenching in the solid state due to the peripheral aromatic rings preventing π–π stacking interactions, as evidenced by single-crystal X-ray analysis. Moreover, its rod-like microcrystals exhibit excellent optical waveguide properties. Hence, c-TPE-ON comprises a N-PAH with unprecedented luminescent properties and as such is a promising candidate for fabricating organic optoelectronic devices. Our design and synthetic strategy might lead to a more general approach to the preparation of solution- and solid-state luminescent PAHs.

Unprecedented luminescence: A luminescent nitrogen-containing polycyclic aromatic hydrocarbon (N-PAH) has been synthesized from a vinylene-based AIEgen by a photocyclodehydrogenation reaction with unexpected regioselectivity. The N-PAH exhibits excellent optical properties both in solution and in the solid state (see figure).

An original samarium(III) complex based on a triazacyclononane platform functionalized with a charge-transfer antenna chromophore exhibited optimized brightness and was successfully used as an emissive species for two-photon microscopy experiments in both the visible and near-infrared spectral ranges.

Wide-range imaging: An original samarium(III) complex based on a triazacyclononane platform functionalized with a charge-transfer antenna chromophore exhibits optimized brightness and can be successfully used as an emissive species for two-photon microscopy experiments in both the visible and near-infrared (NIR) spectral ranges (see figure).

Two pairs of enantiomeric compounds with formulas (S)- or (R)-Co₃(ppap)₂(4,4′-bpy)₂(H₂O)₂⋅4 H₂O [(S)-1 or (R)-1], (S)- or (R)-Co₃(ppap)₂(4,4′-bpy)₂(H₂O)₂⋅3 H₂O [(S)- or (R)-2), and related racemic compound Co₃(ppap)₂(4,4′-bpy)₂(H₂O)₂⋅4 H₂O (rac-3; 4,4′-bpy=4,4′-bipyridine, H₃ppap=3-phenyl-2-[(phosphonomethyl)amino]propanoic acid) are reported. Compounds 1 and rac-3 show identical three-dimensional framework structures, whereas compounds 2 have two-dimensional layer structures. Compounds 1 and 2 are catenation isomers, formation of which is controlled solely by the pH of the reaction mixtures, whereas the formation of isomeric compounds 1 and rac-3 is controlled purely by the chirality of the phosphonate ligand. The magnetic properties of fully dehydrated (S)-1, (S)-2, and rac-3 are highly dependent on both structure and chirality.

Five isomeric compounds (S)- or (R)-Co₃(ppap)₂(4,4′-bpy)₂(H₂O)₂⋅4 H₂O, (S)- or (R)-Co₃(ppap)₂(4,4′-bpy)₂(H₂O)₂⋅3 H₂O, and racemic Co₃(ppap)₂(4,4′-bpy)₂(H₂O)₂⋅4 H₂O (4,4′-bpy=4,4′-bipyridine, ppapH₃=3-phenyl-2-[(phosphonomethyl)amino]propanoic acid) are reported, the formation of which is controlled by the pH of the reaction mixture or by the chirality of the phosphonate ligand (see figure). Their magnetic properties were studied.

Two different conjugated microporous polymers (CMPs) based on tetrakis(4-ethynylphenyl)stannane as the repeating unit were synthesized and their BET surfaces and thermal properties were investigated. The first direct method to elucidate the molecular structure of the organic linkers between the tin centers by digestion of the CMP is described. Selective cleavage of the tin–carbon bonds with chloroacetic acid afforded the isolated bridging units and provided insight into the surprisingly varied chemical composition of these networks.

Burn your bridges: Two different conjugated microporous polymers (CMPs) based on tetrakis(4-ethynylphenyl)stannane as the repeating unit were synthesized and characterized. Selective cleavage of the tin–carbon bonds with chloroacetic acid affords the isolated bridging units, thereby providing insight into the structure of the organic linkers and the surprisingly varied chemical composition of these networks.