A comparative analysis of the influence of the molecular structure and medium properties on the photostability and efficiency of singlet oxygen generation by luminophores based on iodo- and bromosubstituted zinc(II), cadmium(II) and boron(III) dipyrromethenates is presented. It has been established that photodestruction of halogen-substituted complexes [ZnL2], [CdL2], and [BF2L] includes the initial stages of dehalogenation of luminophores and is a process of photosensitization, the efficiency of which depends both on the molecular structure of the chelates and on the medium properties. Based on experimental and literature data, the mechanism of 1O2 generation with the participation of iodo- and bromosubstituted dipyrromethenates [ZnL2], [CdL2] and [BF2L] was proposed and substantiated. It was shown that the indices of photostability and generation of singlet oxygen by heteroligand boron chelates [BF2L] are approximately 33 and 8 times higher, respectively, than the corresponding characteristics of homoligand complexes [ZnL2] and [CdL2]. The influence of the halogenation features is manifested in an increase of the photodegradation efficiency upon the transition from 2-monoiodo- to 3,5-dibromo- and 2,6-dibromosubstituted dipyrromethenates of zinc(II), cadmium(II) and boron(III) due to a decrease in the probability the transition to a triplet excited state and a decrease in the efficiency of singlet oxygen generation. The combination of the high photostability rates and singlet oxygen generation provides a good practical potential for the use of iodo- and bromosubstituted zinc(II), cadmium(II), and boron(III) dipyrromethenates as PDT agents.

The results obtained over the past two decades by the staff of the Institute of Solution Chemistry, RAS, and future promising developments in the field of physical, inorganic, and supramolecular chemistry of dipyrromethene dyes and luminophores have been briefly described. The major attention is paid to the spectral and other practically significant characteristics of dipyrromethene ligands, salts, and stable coordination compounds responsible for their properties of chromophore and fluorescent chemosensors of analytes of various nature.

Crystal solvates of zinc(II) 3,3',5,5'-tetramethyl-4,4'-dibromo-dipyrromethenate [ZnL2] form supramolecular complexes [ZnL2(C2H5OH)(2)] and [ZnL2(DMF)(2)] with molecules of ethanol and DMF. Such complexes are stable up to similar to 150 and 111 degrees C, respectively. According to the quantum chemical calculations, [ZnL2(DMF)(2)] is formed due to the additional coordination of molecular ligands by the zinc atom (Zn delta(+) <- : O). In the case of [ZnL2(C2H5OH)(2)], along with weak coordination interactions of the hydroxyl group oxygen with the zinc ion, the main contribution to the suprastructure formation is made by hydrogen bonds (C2H5OH <- :N <=), which makes both the destruction onset temperature and the total enthalpy (Delta H-Sigma) of the intermolecular interactions in [ZnL2(C2H5OH)(2)] much higher than in [ZnL2(DMF)(2)]. The obtained results are interesting for the development of new [ZnL2] fluorescent sensors of N- and O-containing analytes.

We have obtained a new water-soluble form of boron(III) dipyrromethene luminophores using the example of 3,3',5,5'-tetraphenyl- ms -aza-2,2'-dipyrromethenate boron(III) (BODIPY) and Cremophor® (polyethylene glycol, PEG-40). The results of a study of the spectral-luminescent properties of the studied BODIPY–Cremophor®–aqueous–alcohol medium system are presented. It is found that Cremophor® is the only one of a series of investigated excipients (PEG-400, PEG-1000, polyvinylpyrrolidone, bovine serum albumin, sodium carboxymethylcellulose) providing solubilization of BODIPY in an aqueous medium, while maintaining its intense spectral characteristics, including fluorescence and luminophore, in the red region of the spectrum. The BODIPY–Cremophor® system is tested on two mouse cell lines: metastatic breast cancer and non-metastatic skin cancer. It is shown that the introduction of the BODIPY–Cremophor® system into both cell lines of mice leads to the detachment of cell cultures from the substrate and suppression of the development of cancerous tumors. The results obtained show that immobilization of BODIPY in PEG-40 in an aqueous-alcoholic medium makes it possible to obtain preparations with prolonged action, which can be used as photosensitizers (PSs) in photodynamic therapy and for bioimaging in cell biology.

It is well known that boron-dipyrromethene (BODIPY) dyes have a remarkable combination of photophysical and photochemical properties, which are significant for practical use. Unfortunately, the application of BODIPYs in optical devices and biosensorics is severely limited due to the aggregation quenching effect (ACQ), the effects of the internal filter and/or the formation of excimers. One way to prevent fluorescence quenching is to synthesize new molecules BODIPY with a highly complicated structural organization or hybrid systems based on them. But in this paper, we demonstrate that the introduction of simple aliphatic or aryl substituents into the ms-position of the BODIPY molecule is an effective way to control the aggregation in various states: thin mono- and multilayer Langmuir-Schaefer (LS) films, polymer films and concentrated solutions, including aqueous ones. The results of experimental studies of the aggregation behavior of BODIPYs (BDP1-BDP3) are in good agreement with the theoretical calculations data of di- and tetramers, as well as multilayer packing. This allows to adjust the spectral properties of luminophores to the most possible types of their real applications in practical areas.

An analysis and interpretation of experimental and theoretical data on the spectral-luminescent, photophysical, and photochemical properties of dipyrromethenates are presented depending on the structure of the ligand, the complexing agent type, and the solvent and its phase state (temperature). The special features of photonics related to the violation of the physicochemical properties in the series of substituted dipyrromethenates in heteroatoms and heavy atoms (their nature, location, and the number of such substituents) are discussed.

The results of investigation of the spectral characteristics, photostability and thermal degradation of B(III) and Zn(II) complexes with 3,3',5,5'-tetramethyl-2,2'-dipyrromethene and meso-phenyl-3,3',5,5'-tetramethyl-2,2'-dipyrromethene were presented. It has been shown that meso-phenyl substitution in the 3,3', 5,5'-tetramethyl-2,2'-dipyrromethene complexes with B(III) and Zn(II) leads to a hypsochromic displacement S-0 -> S-1 bands in the EAS and a significant increase in its intensity, but a decrease in the fluorescence quantum yield. It has been established that the introduction of phenyl substituent in the meso-position causes an increase in thermal stability (up to 20 degrees C in Bodipy and up to 74 degrees C in Zn-complexes) and photostability (up to 3 times for Bodipy and up to 7 times for Zn(II) dipyrromethenates).

Photonics of complexes of p- and d-elements with dipyrromethenates is investigated. The role of substituents (their type and localization in the ligand) and of the medium in which dipyrromethenates are placed (solvents, gas mixtures, or solid matrices) is discussed as well as the effect of complexing agents on photonics of the examined complexes. The possibilities for dipyrromethenates application as liquid and solid state laser active media, sensor media for determining the oxygen concentration in a gas mixture, and photosensitizers for singlet oxygen generation in optical devices are presented.

The spectral luminescent properties of a series of zinc dipyrromethenate [Zn(dpm) 2 ] with alkyl-, phenyl-, meso-aza-, and halogen substituents in the ligand are studied in solutions in ethanol (neutral and acidified with hydrochloric acid). The stability of the complexes in proton-donor solvents in the ground and excited states is investigated, and quantum yields of laser-induced phototransformations are measured. In a number of cases, a relationship between the photochemical stability of the investigated dipyrromethenates and their properties in proton-donor media is found and discussed.

The results of investigation of the photostability and thermal degradation of B(III), Zn(II), Cd(II) complexes with monoiodo-and dibromosubstituted dipyrrins of the composition [BF2L] and [ML2] were presented. The processes of photo-and thermal degradation of complexes includes the initial stages of dye molecules dehalogenation. In general, the replacement of 4-iododipyrrin ligand by 5,5 '-dibromo-and 4,4 '-dibromosubstituted analogs in the composition of complexes [BF2L] and [ML2] promotes an increase in the photo-and thermal stability of the dyes. The replacement of the saturate hydrocarbon (cyclohexane) with the aromatic analogue (benzene) leads to a significant decrease in the photostability of [BF2L] and [ML2] because of polarization of the chromophore systems of dye molecules due to p-p stacking with aromatic solvent molecules. The thermal destruction start temperatures [ML2] and [BF2L] in the argon atmosphere range from 179 to 275 degrees C and strongly depend on the nature and efficiency of the participation of complexing and halogen atoms in intramolecular redox reactions. Complexes [BF2L], which showed the greatest photostability in solutions, differ the least thermal stability in the solid phase. The observed differences are due to the specific structural effects and different mechanisms of the photo-and thermal degradation processes under various environmental conditions.

Photostability of B(III), Zn(II), Cd(II) complexes with monoiodo- and dibromosubstituted dipyrromethenes [BF 2 L] and [ML 2 ] in benzene and cyclohexane solutions is studied. It is found that the mechanism of destruction of the dyes under UV radiation is based on participation of singlet oxygen generated by the excited triplet state of the dye. Singlet oxygen enters the oxidation reactions of the pigment molecules leading to accumulation of colorless products based on di-, monopyrrol, and smaller fragments. Initial stages of the process include the reactions of dehalogenation of the dye molecules and are accompanied by enhancement of the fluorescence of the formed alkyl-substituted dipyrromethenates. The photostability of boron complexes [BF 2 L] is up to 32 times higher as compared to that of [ZnL 2 ] and [CdL 2 ]. The replacement of 4-iododipyrromethene ligands in [BF 2 L] and [ML 2 ] by 5,5'-or 4,4'-dibromo-substituted ligands increases photostability of the dyes. The stability of the dyes against UV irradiation substantially decreases in benzene with respect to cyclohexane due to enhancement of polarization of the chromophore systems of dipyrromethene ligands because of their solvation with benzene ( π – π -stacking).

Cadmium(II) chelates with 4-iodo-, 5,5´-, and 4,4´-dibromo-2,2´-dipyrromethenes (HL 1 , HL 2 , and HL 3 , respectively) with the composition of [CdL 2 ] were synthesized. The influence of structural features of their molecules and properties of the medium on the characteristics of absorption and fluorescence spectra, and also on the thermodynamic stability constants in solutions was evaluated. The results of quantum chemical calculations revealed that the additional coordination interactions between the bromine atoms at the α-positions of dipyrromethene ligands and the complexing atom are possible in the molecular structure of α,α´- dibromosubstituted dipyrromethenate [Cd(L 2 ) 2 ] in contrast with β-halogenated analogues [Cd(L 1 ) 2 ] and [Cd(L 3 ) 2 ].