Ivan Petkov

Synthesis and spectral properties of new N-substituted naphthalimide luminophores for structural coloration of polymethylmethacrylate and polystyrene

Two new unsaturated acryloxide derivatives of 4-amino-substituted-1,8-naphthalimide luminophores were synthesized. Their absorption and fluorescent properties were determined in both CHCl 3 and C 2 H S OH. The luminophores display a broad absorption band in the visible spectral region (halfband-width up to 4433 cm -1) and a fluorescence in the yellow-green region (526-530nm). The compounds are yellow colored, with a high brightness (from 2.92 up to 6.75 ) and a purity of color. The possibility of including naphthalimide luminophores in copolymerization process with ST and MMA resulting in the formation of colored polymers was investigated. It was found that no changes in the chemical structure of the chromophore group occurred during copolymerization. More than 92% of the initial luminophores were bound to the polymer chain. The influence of the luminophores on the kinetics of polymerization was studied, and the average viscosimetric molecular weight, M v , of the obtained colored polymers estimated.

On the photosensitivity of dibenzoylmethane, benzoylacetone and ethyl benzoylacetate in solution

Abstract The influence of sunlight on the keto-enol ratio of dibenzoylmethane, benzoylacetone and ethyl benzoylacetate in heptane solution was examined. It was shown that the tautomeric equilibrium is strongly displaced to the keto form. Important differences in the photosensitivity of β-diketones and β-ketoesters depending on the structural features and the nature of irradiation have been established.

Photochromism of styryl cyanine dyes in solution

Abstract The photochemical and spectral behavior of two styryl cyanine dyes were studied in different solvents. The experimental results indicate that in solution the compounds exist in two forms—closed and open. The equilibrium is strongly shifted toward the closed form. From the absorption and luminescence properties, the conclusion can be made that absorbed energy can be lost through different channels:photochemical closed—open form and cis—trans isomerization and through photophysical processes such as fluorescence. The quantum yield of the process, closed—open form is measured. The reasons for the photochromic behavior of these compounds are discussed.

Effect of some 2-arylbenzothiazoles on the photo-degradation of poly(vinyl chloride)

The action of some 2-phenyl-benzothiazoles (BT) as photo-sensitizers of the photo-degradation of poly(vinyl chloride) (PVC) is studied. On irradiation with unfiltered light in air, polyene sequences are formed. The initial dehydrochlorination of PVC as well as the development of polyene sequences strongly depend on the nature of the compounds. Complexes ((BTH)+ Cl−) formed from BT and HCl (liberated from the photo-dehydrochlorination of PVC) are observed. The role of these complexes is discussed and their effect on the physical and mechanical properties of PVC is considered. The data can be explained by the strong acceptor action of the excited states of BT.

Tautomerism of rhodanine

Semiempirical (MINDO/3, AM1, PM3, MNDO) and ab initio (4-31G and 4-3IG + dAO/S basis sets) calculations on the relative stabilities and structures of the five potential tautomeric forms of rhodanine are reported. It is shown that all methods (excepting PM3) predict as most stable 2-thioxo-4-thiazolidinone. These results correspond to the known experimental data. The infrared spectrum of rhodanine was recorded for the region 4000-150 cm−1, and the characteristic bands were compared with AM1 and 4-31G + dAO/S calculated frequencies. The transition states between five pairs of all possible tautomeric forms of the rhodanine were found by the AM1 method.

Synthesis and properties of fluorescent bis-quaternized perylene dyes

Abstract A series of perylene dyes containing aliphatic trialkylamino and quaternary ammonium groups has been prepared. Perylene dyes containing trialkylamino groups were virtually nonfluorescent Quaternization of the trialkylamino groups with alkyl iodide resulted in an increase in the fluorescence (Q f = 0.8–0.9); the same phenomenon was observed by protonation of the trialkylamino groups in acid media.

Synthesis and Photophysical Properties of Yellow-Emitting Iridium Complexes. Effect of the Temperature on the Character of Triplet Emission

The parent study includes synthesis end photophysical characterization of four new phosphorescent cyclometalated iridium (III) complexes. The cyclometaled ligands used here are 2-(4-chlorophenyl)benzo[d]thiazole, 2(4isopropylphenyl)benzo[d] thiazole, 2-(4-methoxyphenyl)benzo[d]thiazole, 4-(benzo[d]thiazol-2-yl)-N,N-dimethylaniline. The auxiliary ligand is acetylacetone (Hacac). The photometric analyses show temperature dependence on phosphorescent spectra and the nature of the emitting state of the synthesized complexes. Using fluorescent and absorption spectroscopy we suggest an explanation of the observed effect points out the transition from ligand centered (LC) to MLCT main character of the emitting state. The quantitative photometric analysis states high phosphorescent quantum yields of the complexes in solution.

Photophysical properties of novel fluorescent poly(oxyethylene phosphate) tris(β-diketonate) europium (III) complexes

In the present study, photophysical properties of fluorescent poly(oxyethylene phosphate) tris(beta-diketonate) europium (III) complexes have been studied by means of stationary and time-resolved fluorescence spectroscopy (in ethanol at room temperature). The luminescent quantum yields and efficiency for the energy transfer from beta-diketonate ligands to Eu(III) ion have been determined for the studied complexes by using diffusion-enhanced fluorescence resonance energy transfer. Obtained results show effect of the polymer ligands upon photophysical properties of the complexes and a relation has been established with length of the oxyethylene spacer between two phosphonate groups. The Förster radiuses of the synthesized compounds with SulfoRhodamine 101 as acceptor have been calculated. Measured distances between molecules of the donors and acceptor at identical acceptor/donor molar ratios have been illustrated the difference in structure of the ternary and polymer complexes in solution even at low concentration.

Photochemistry of 2-[(1,3,3-trimethylindoline-2(1H)-ylidene)propen-1-yl]-3,3-dimethylindolino[1,2-b]-oxazolidine in solution

Photochemical behavior of 2-[(1,3,3-trimethylindoline-2(1H)-ylidene)propen-1-yl]-3,3-dimethylindolino[1,2-b]-oxazolidine was investigated in different solvents. The results obtained indicate that in solution the compound may exist in the two forms (closed and open forms) depending on solvent polarity and proticity. Solvent and structure effects on the closed → open form process were studied. The mechanism responsible for the stabilization of the open form is discussed.

Photoketonization and excited state relaxation of dibenzoylmethane in non-polar solvents

Abstract The ketonization process of dibenzoylmethane is studied experimentally by continuous lamp and pulsed laser radiation over a wide concentration range. It is found that the ketonization rate constant does not depend on the concentration below 0.05 mol m −3 but does depend on it above 0.05 mol m −3 . The relaxation rate constants of the excited enol form have been measured in the same concentration range with a nanosecond and a picosecond pump—probe absorption apparatus. Using the kinetic data obtained, a model for the ketonization mechanism is proposed. The ketonization process is determined by a direct hydrogen transfer (with a rate constant equal to 1.8 × 10 5 s −1 from the excited enol molecule, and after formation of an excited complex between one excited and one non-excited enol molecule. The low quantum yield of fluorescence of the enol-form molecule is explained by the fast isomerization from the first excited singlet state with a rate constant of 4.7 × 10 10 s −1 .