M. B. Berezin

The computational and experimental investigations of photophysical and spectroscopic properties of BF2 dipyrromethene complexes

The electronic excited states of BF2 dipyrromethene (2BrDPM, DPMI, DPMII, PM567 and 4PhDPM) complexes were investigated using the extended multi-configuration quasi-degenerate at the second order of perturbation theory (XMCQDPT2) and the second-order approximate coupled-cluster (CC2) methods. The excitation energies calculated by CC2 are significantly overestimated by 0.42-0.59 eV because of the substantial contributions of double excitation levels to excited states (>10%). However, the calculated XMCQDPT2 excitation energies agree well with experimental ones within the accuracy 0.11-0.20eV. The very low lasing efficiency (7.8-8.4%) of 4PhDPM compound was explained by the T1→T4 and T1→T5 reabsorptions at XMCQDPT2 level of theory. The molecular photonics of pyrromethenes are studied using a combination of the first-principle and semi-empirical calculations. The main mechanism for the deactivation of the energy of the first singlet excited electronic state is the radiative electronic transition for DPMI, DPMII, PM567 and 4PhDPM compounds. Also, the main mechanism for the quenching of fluorescence in considered complexes (except DPMII compound) is the internal conversion. The processes of the internal conversion and intersystem crossing compete with each other in DPMII compound. The measured and calculated fluorescence quantum yields agree well for all considered molecules.

Characteristic features of formation, synthesis, and properties of binuclear zinc(II) helicates with alkyl-substituted 3,3′-bis(dipyrrolylmethenes)

On the basis of spectrophotometric studies, it was demonstrated that complexation of hydrobromides of seven alkylated 3,3′-bis(dipyrrolylmethenes) (H2L · 2HBr) with zinc(II) acetate dihydrate in DMF (298.15 K) includes successive steps of formation of binuclear helicates of two types: [Zn2(AcO)2L] (heteroleptic single-helix complex) and [Zn2L2] (homoleptic double-helix complex). An increase in the degree of alkylation of the pyrrole rings of the ligands from 4 to 10 methyl groups induces an increase of overall complexation constants from 7.60 to 13.73. The synthesis of helicates [Zn2L2] was described. The products were studied by elemental analysis and IR, 1H NMR, U/Vis, and fluorescence spectroscopy. The effect of the helicand structure and the solvent nature on the chromophore and fluorescence properties of [Zn2L2] was discussed. The kinetic stability of zinc(II) with decamethyl-substituted 3,3′-bis(dipyrrolylmethene) in HCl-DMF medium was estimated.

Thermal oxidative degradation of the functionally substituted 2,2′-dipyrrolylmethenes hydrobromides and difluoroborates

Thermal oxidative decomposition of samples of crystalline hydrobromide and borofluoride complexes (BODIPY) of a series of 2,2′-dipyrrolylmethenes (HL) was studied by means of thermogravimetry in an atmosphere of air oxygen. An increase in the degree and symmetry of substitution, aromaticity, and the length of the substituents in 4,4′-positions of the pyrrole ligand rings increases stability of the BODIPY-dyes to oxidative degradation. A comparative analysis of the influence of structural factors on the thermolability of hydrobromdes (HL·HBr), d-metal (ML2) and boron(III) complexes with 2,2′-dipyrrolylmethenes was carried out.

Kinetics of the Dissociation of Transition Metal Complexes with α,α-Dipyrrolylmethene in Acetic Acid–Benzene as a Binary Proton-Donating Solvent

The kinetics of the dissociation of Co(II), Ni(II), and Zn(II) complexes with 4,4′-dibutyl-3,3′,5,5′-tetramethyldipyrrol-2,2′-ylmethene was studied in acetic acid–benzene as a binary proton-donating solvent. The metal nature was found to affect the kinetic parameters of the process. Assumptions were made about the limiting step of the process and the effectiveness of d metal ions in the template synthesis of porphyrins from dipyrrolylmethenes.

Comparative analysis of physicochemical properties of dinuclear zinc(II) helicates with 2,2′-, 2,3′-, and 3,3′-bis(dipyrromethenes)

The effect of the attachment position of a methylene spacer in 2,2′-, 2,3′-, and 3,3′-bis(dipyrromethene) N4-ligands (H2L) on physicochemical properties of their dinuclear homoleptic helicates [Zn2L2], such as specific features of their molecular structure, luminescence spectral characteristics, lability in acid solutions, and thermal stability in an argon atmosphere, has been examined. It has been shown that the substitution of the biladiene-type helicand by its 2,3- and especially 3,3′-analogues leads to a considerable enhancement of the chromophoric properties, an increase (up to 30-fold) of the fluorescence quantum yield, and an increase in the stability of corresponding dinuclear helicates [Zn2L2].

meso-spacer influence on properties of zinc(II) complexes with 2,3′- and 3,3′-bis(dipyrrolylmethenes)

The study and comparative analysis of spectral-luminescent characteristics (absorption and fluorescence spectra), of quantum yield, and fluorescence life time in solutions, of lability in proton-donor media, solid phase thermal stability in air oxygen and argon was carried out for binuclear zinc(II) helicates with decamethyl-substituted 2,3′- and 3,3′-bis(dipyrrolylmethenes). The influence of molecular structure features of the ligands on the physicochemical properties of helicates was discussed.

Thermochemistry of solution of some quaternized derivatives of tetra(4-pyridyl)porphine in water

Quaternized tetra(4-pyridyl)porphine derivatives: tetra(N-carboxymethyl-4-pyridyl)porphine tetrachloride, tetra(N-carboxymethyl-4-pyridyl)porphine tetrabromide, tetra(N-methyl-4-pyridyl)porphine tetraiodide, and tetra(N-ethoxycarbonylmethyl-4-pyridyl)porphine tetrachloride, were synthesized, isolated, and purified. The enthalpies of solution of these compounds in water at 298.15 K were determined calorimetrically. The effect of functional substituents in porphyrin ligands on the enthalpies of solution is discussed.

Photonics of zinc(II) and boron(III) chelates with methyl- and phenyl-substituted dipyrromethenes and azadipyrromethenes

A comparative study of spectral, luminescent, and photophysical parameters has been carried out for a series of zinc(II) and boron(III) chelates with dipyrromethene ligands of a similar structure: tetramethyl- and tetraphenylpyrrodimethenes bearing the substituents on the pyrrole rings and tetraphenylazapyromethene. In some cases, the luminescence efficiency of the chelates depends on the excitation wavelength. The replacement of the central atom boron(III) by zinc(II) results in not only a twofold increase in the number of coordinated chromophoric ligands and the absorption coefficient, but also an increase in the contribution of nonradiative processes to excitation energy deactivation and, hence, a decrease in the yield of fluorescence. The efficiency of intersystem crossing is higher in the zinc(II) dipyrromethene complexes than in the corresponding boron-chelated dipyrromethenes (BODIPYs), resulting in the appearance of phosphorescence in frozen solutions. It has been found that the replacement of the meso-spacer in the dipyrromethene ligand by the nitrogen atom not only shifts the absorption and fluorescence band maximums to longer wavelengths, but also decreases the fluorescence efficiency and leads to the appearance of long-lived luminescence even in aza-BODIPY. An analysis of the results has shown that these behavior can be due to involvement of the nπ* (πσ*, σπ*) states localized on the meso-nitrogen in the deactivation of excitation energy.

Synthesis and spectral properties of the nickel(II) and mercury(II) helicates with 3,3′-bis(dipyrrolylmethenes)

The influence of the nature of the complexing metal on the optical properties of coordination compounds of bis(dipyrrolilmethenes) was studied.

Synthesis and photophysical properties of Cd(II) and Cu(II) complexes with decamethylated bis(dipyrrolylmethene)

Copper(II) and cadmium(II) complexes with bis(2,4,7,8,9-pentamethyldipyrrolylmethene-3-yl)-methane were synthesized. Influence of the complex-forming ion nature on the optical properties of [Cd2L2] and [Cu2L2] helicates was studied.