Structure, electronic and vibrational spectra and aromaticity of hemiporphyrazine and its hydrates: A density functional theory study

A Switchable Near-Infrared-Absorbing Dye Based on Redox-Bistable Benzitetraazaporphyrin

Activatable near-infrared (NIR) dyes responsive to external stimuli are used in medical and other applications. Here, we describe the design and synthesis of bench-stable 18π- and 20π-electron benzitetraazaporphyrins (BzTAPs) possessing redox-switchable NIR properties. X-Ray, NMR, and UV/Visible-NIR analyses revealed that 20π-electron BzTAP 1 exhibits NIR absorption and antiaromaticity with a paratropic ring-current, while 18π-electron BzTAP 2 shows weakly aromatic character with NIR inertness. Notably, the NIR-silent BzTAP 2 was readily converted to the NIR-active BzTAP 1 in the presence of mild reducing agents such as amine. The intense NIR absorption band of BzTAP 1 is in sharp contrast to the very weak absorption bands of previously reported antiaromatic porphyrinoids. Molecular orbital analysis revealed that symmetry-lowering perturbation of the 20π-electron porphyrinoid skeleton enables the HOMO-LUMO transition of 1 to be electric-dipole-allowed. BzTAPs are expected to be useful for constructing activatable NIR probes working in reductive environments.

The synthesis and characterization of ylideneisoindolinones

1,3-Diiminoisoindoline (DII) and the closely related molecule, iminoisoindolinone are important precursors in the synthesis of macrocycles and chelates such as phthalocyanines, and bis(arylimino)isoindolines, as well as chromophores including aza-BODIPY dyes. A series of seven ylideneisoindolinones are presented in this report. The reaction of various organic CH acids and iminoisoindolinone produce compounds that show strong [Formula: see text]* transitions in the UV region. The chromophores have been characterized spectroscopically and the X-ray structures show electronic delocalization across the chromophore. Additionally, DFT and time-dependent DFT calculations confirm the lower energy absorbances are primarily HOMO-LUMO transitions.

Ring-Opened Hemiporphyrazines: Helical Molecules Exhibiting Circularly Polarized Luminescence

We designed and synthesized a new type of small helical molecule exhibiting intense circularly polarized luminescence (CPL) (1_2H ) by modifying a 20π-electron hemiporphyrazine with a large transition magnetic dipole moment. The hemiporphyrazine ring was opened and one additional pyridine unit was introduced, resulting in an overlap of two pyridine rings. X-ray structure analysis confirmed that 1_2H and its zinc complex (1_Zn ) adopt a helical geometry. A racemic mixture of 1_Zn was resolved into two enantiomers ((P)- and (M)-1_Zn ), which exhibited CPL with a high luminescence dissymmetry factor (g_lum ) value of ±2.1×10^-2 . The origin of the large g_lum value was rationalized by means of DFT calculations. Helical structures could be formed in a diastereoselective manner by covalently attaching chiral units to the skeleton (1'_2H and 1'_Zn ). 1_Zn was found to possess chiral recognition ability for amines.

Biliazine: a ring open phthalocyanine analog with amesohydrogen bond

The hemiporphyrazine type chelate and phthalocyaninine analog biliazine (H₂BlzH) and its metal complexes can be synthesized in one-step from a monosubstituted diiminisoindoline (DII).

Microwave-assisted synthesis and sublimation enthalpies of hemiporphyrazines

It was established that microwave irradiation solvent-free processing of 2,6- diaminopyridine or 1,3-phenylenediamine with phthalonitrile or 4-tert-butylphthalonitrile led to corresponding hemiporphyrazines with sufficiently high yields and a huge reduction in the time required for synthesis, from 8–12 h to 20 min. The data of IR and UV-vis spectroscopies and elemental analysis of the final products were found to be similar to those described in literature. The obtained hemiporphyrazines were characterized by 1H and [Formula: see text]C NMR data. We applied the Knudsen effusion method with mass spectrometric control of vapor composition. The mass spectrometric investigations established that the macrocyclic compounds give a stable stream of particles and their enthalpies of sublimation were estimated by the second law of thermodynamics.

Excitonic luminescence of hemiporphyrazines

Metal-free hemiporphyrazine (HpH(2)) is a notoriously insoluble material possessing interesting photophysical properties. Here we report the synthesis, structure, and photophysical properties of an octahedral zinc trans-ditriflate hemiporphyrazine complex "HpH(2)Zn(OTf)(2)" that contains a neutral hemiporphyrazine ligand. The photophysical properties of hemiporphyrazine are largely unaffected by introduction of zinc(II) triflate, but a dramatic increase in solubility is observed. HpH(2)Zn(OTf)(2) therefore provides a convenient model system to evaluate the impact of aggregation on the photophysical properties of hemiporphyrazine. Soluble aggregates and crystalline materials containing planar hemiporphyrazines exhibit relatively strong absorbance of visible light (450-600 nm) and red luminescence (600-700 nm). Hemiporphyrazine monohydrate (HpH(2)·H(2)O), in contrast, has a nonplanar "saddle-shaped" conformation that exhibits very little absorbance of visible light in solution or in the solid state. Upon photoexcitation at 380 nm, HpH(2)Zn(OTf)(2) and HpH(2) exhibit multiwavelength emissions centered at 450 and 650 nm. Emissions at 450 nm are highly anisotropic, while emissions at 650 nm are fully depolarized with respect to a plane-polarized excitation source. Taken together, our results suggest that excitonic coupling of aggregated and crystalline hemiporphyrazines results in increased absorbance and emission of visible light from S(0) ↔ S(1) transitions that are usually symmetry forbidden in isolated species. In contrast to previously proposed theories involving excited-state intramolecular proton transfer, we propose that the multiple-wavelength luminescent emissions of HpH(2)Zn(OTf)(2) and HpH(2) are due to emissive S(1) and S(2) states in aggregated and crystalline hemiporphyrazines. These results may provide a better understanding of the nonlinear optical properties of these materials in solution and in the solid state.