Five substituted 2-aryl-4-hydroxy-5-(2'-aminophenyl)-1,3-thiazoles have been studied for their fluorescence properties under neutral and alkaline conditions in solutions of various organic solvents. From comparison with the analogous 2-aryl-4-hydroxy-5-(2'-hydroxyphenyl)-1,3-thiazoles it is clear that both in neutral as well as in the deprotonated state the presence of the 2'-amino group lowers the fluorescence quantum yields (Phi). Introduction of an electron withdrawing groups into the 2-aryl group further decreases Phi. Upon deprotonation of the 4-hydroxy group a large bathochromic shift of the absorption (Delta lambda(A)=100-125 nm) as well as emission (Delta lambda(F)=100-120 nm) bands occurs. An intramolecular hydrogen bond between the amino and hydroxyl groups is obvious. The first absorption band of all studied compounds corresponds to a pi-pi* HOMO-LUMO transition with a CT character. Thiazoles 3b-f and their deprotonated forms 3b(-)-f(-) display fluorescence properties with large Stokes shift (ca 9000 cm(-1) and 6000 cm(-1), respectively) and moderate quantum yields (0.11-0.41), both are connected with the presence of inter and intramolecular hydrogen bonds.(C) 2018 Elsevier B.V. All rights reserved.

Six novel oxazaborines based on 7-aminocoumarin substituted by either fluoride or phenyl group on the boron atom were prepared from the corresponding enaminones. The compounds were characterized by means of 1H, 13C, 19F, and 11B NMR in solution, X-ray diffraction in crystal, UV–Vis spectroscopy, and electrochemistry. The observed optical properties were compared to the DFT calculations. Dynamic behaviour of selected oxazaborines was studied by means of 19F and 1H VT NMR and 2D EXSY. Both the enaminones and oxazaborines exhibit relatively strong fluorescence both in solid state and in frozen 2-methyltetrahydrofuran at 77 K, but none in solution. In some cases, phosphorescence was observed as well. Preliminary aggregation tests revealed aggregation induced emission (AIE) properties of the studied molecules. Concerning the electrochemical properties, the first reduction of all the oxazaborines studied proceeds as transport controlled one-electron (quasi)reversible process whereas the first oxidation of BPh2 oxazaborines proceeds as a two-electron irreversible process most probably of the ECE type. The oxidation of BF2 compounds was not possible to obtain within the given potential window. Analysis of frontier orbitals showed that change from BF2 to BPh2 leads to decrease of energy gap.

This study is focused on explanation of the remarkable photophysical behaviour of the 1-(4,6-dichloro-1,3,5-triazin-2-yl)-pyrene (PyTC2) compound which has been introduced as a fluorescent polarity probe. This compound exhibits large solvatochromic red-shift of fluorescence emission band while maintaining high fluorescence quantum yield and monoexponential decay kinetics throughout the whole solvent polarity scale. As the semi-empirical calculations reported in the original paper have not revealed any excited state possessing a high dipole moment, it has been suggested that the red-shift originates from planarization of the emitting excited state in polar solvents in contrast to unchanged twisted geometry in non-polar solvents. However, both the extent of the red-shift and the disappearance of the vibronic structure in polar solvents indicate that the emission originates from an excited state with high dipole moment and that the semi-empirical methods may not be sufficient to describe the emitting state of this molecule correctly. Thus, we have performed TD-DFT calculations including the potential energy surface scans. According to these calculations and scans, the emission takes place from a planarized intramolecular charge-transfer (ICT) state. This is in good agreement with all aspects of the observed fluorescence behaviour of PyTC2. Independent experimental evidence for the ICT has been provided by analysis of resonance Raman intensities where bands corresponding to enhanced normal modes residing on triazine and the stretching mode between pyrene and triazine moieties have been identified. The formation of the photoinduced ICT together with easy and inexpensive preparation make this compound and its derivatives candidate as push-pull building blocks for the design of advanced functional materials.

Eight substituted 2-aryl-4-hydroxy-5-(2'-hydroxyphenyl)-1,3-thiazoles have been prepared and their fluorescence properties have been investigated under neutral and alkaline conditions in solutions of various organic solvents. From the comparison with analogous 4-hydroxy-2,5-diphenyl-1,3-thiazole it is clear that both in neutral as well as in the deprotonated state the presence of the 2'-hydroxy group substantially (2-4 times) enhances fluorescence quantum yields (Phi) - most probably due to formation of an intramolecular hydrogen bond. Introduction of an electron withdrawing substituent into the 2-aryl group (2-pyridyl and 4-trifluormethylphenyl derivatives) further enhances Phi up to 0.93 (in dioxane). Upon deprotonation of the 4-hydroxy group a large bathochromic shift of the absorption (Delta lambda(max) = 70 nm) as well as emission (Delta lambda(em approximate to) 110 nm) bands occurs and the Phi-s are typically between 0.3 and 0.7. On the basis of quantum chemical calculations and spectral results, a hydrogen bond interaction between two hydroxyl groups is obvious. The first absorption band of all studied compounds corresponds to pi-pi* HOMO LUMO transition possessing a CT character. (C) 2016 Elsevier Ltd. All rights reserved.

New 1/9- aminoanthracene-triazine-3-aminobenzanthrone bichromophores for the study of excitation energy transfer were synthesized and characterised. Absorption and emission spectra and fluorescence quantum yields were measured. Equilibrium ground state conformations and singlet electronic excited states characteristics were calculated at semiempirical level. A decrease of qF in polar solvents may be explained by the CT state connected with electron transfer from the HOMO localized on the donor to the LUMO spread over the acceptor. A highly efficient energy transfer mediated by through-bond mechanism was observed for all compounds.

Seven model donor-substituted phenyleneethynylene molecules with up to three 1,4-phenylene and two acetylenic units were synthesized by Suzuki–Miyaura and Sonogashira cross-coupling reactions and further studied by absorption and emission spectra and theoretical calculations. The π-system between the N,N-dimethylamino group and terminal acetylene was systematically elongated which allowed elucidation of the fundamental structure–property relationships. Structural factors such as molecular length and chromophore planarity proved to be crucial for the observed spectroscopic behavior.

Novel bichromophoric compounds bearing 2-aminoanthracene as the donor of excitation energy and 3-aminoperylene or 3-aminobenzanthrone as the acceptor of excitation energy and s-triazinyl ring as the spacer were synthesized and characterized. The UV/Vis absorption and fluorescence spectra as well as fluorescence quantum yields in different solvents were measured. On the basis of experimental results and semi-empirical quantum chemical calculations, the relationships between the chemical structure and photo-physical properties of prepared compounds were investigated.

New N-triazinyl derivatives were synthesized by reaction of cyanuric chloride with 1- and 9-aminoanthracenes and subsequent nucleophilic substitution of chlorine atoms on triazinyl ring with methoxy and/or phenylamino groups. The compounds were characterized by 1H and 13C NMR and mass spectra. The influence of the chemical structure and solvent polarity on the UV/Vis absorption and fluorescence spectra and fluorescence quantum yields were investigated. Semi-empirical computations revealed highly polar CT states in singlet excited state manifold connected with charge-transfer from the hydrocarbon moiety to the triazinyl ring. The relationships between the CT-to-emitting state energy gap, solvent polarity and fluorescence quantum yield were discussed.

The geometry and excited state characteristics of five N-triazinyl derivatives of 1-aminopyrene were calculated using AM1, CNDO/S and ZINDO/S methods. For the optimized structures of the studied molecules, Lb, La and Bb transitions (localized on the amino pyrene moiety) were found, as well as charge-transfer states characterized by a charge transfer from the amino pyrene to the triazinyl ring. The energy of such strongly polar charge-transfer states depends on the chemical structure of the compound and on the solvent polarity. The relationships among each charge-transfer-to-emitting state energy gap, solvent polarity and fluorescence quantum yield of the studied compounds are discussed.

Absorption and fluorescence spectra and fluorescence quantum yields of 18 D-;π-A push-pull compounds were measured. The investigated chromophores consist of 4,5-dicyanoimidazole — bearing donor — substituted and systematically extended π-conjugated spacers. The influence of temperature and solvent polarity on the spectral and photophysical properties was investigated. Employing INDO/S calculations, the structure–property relationships were discussed.

N-(4,6-dichloro-1,3,5-triazin-2-yl)-2-aminoanthracene was synthesized by substitution of one chlorine atom of 2,4,6-trichloro-1,3,5-triazine with 2-aminoanthracene. A new series of N-triazinyl-2-aminoanthracenes was prepared by nucleophilic substitution of one or both chlorine atoms on N-(4,6-dichloro-1,3,5-triazin-2-yl)-2-aminoanthracene with electron-donating methoxy or phenylamino groups. The UV/Vis absorption, fluorescence and excitation spectra as well as the fluorescence quantum yields of the prepared compounds were measured in 1,4-dioxane, ethyl acetate, dibutyl ether and acetonitrile; nanosecond kinetics of the fluorescence decay was measured in different solvents. The influence of the character of the substituent on triazinyl ring and of the solvent polarity upon the absorption and fluorescence spectra and fluorescence quantum yields are discussed.

Fluorescence anisotropy measurements were performed on a set of multichromophoric compounds, which contain a different number of aminopyrenyl moieties linked to a triazine ring, in order to reveal the nature of both the electronic excited states and relaxation pathways of the compounds. Our experimental results complement quantum chemical calculations. We propose that the lowest excited state from which fluorescence proceeds is localized on a single individual aminopyrene moiety. In contrast, excitation to a higher excited state is likely followed by a migration of energy to another nearby aminopyrene chromophore before the internal conversion to the emitting state takes place. We suggest that this migration is responsible for the experimentally measured decrease of fluorescence anisotropy of the studied compounds.

N-Acetyl and N-triazinyl 3-aminoperylenes were prepared. N-(4,6-Dichloro-1,3,5-triazin-2-yl)-3-aminoperylene was synthesized by the condensation of 3-aminoperylene with cyanuric chloride; other N-triazinyl derivatives were prepared by the successive substitution of chlorine atoms with methoxy or aniline groups. The structure and purity of the compounds were confirmed by elemental analysis, NMR spectroscopy and mass spectrometry. The UV/vis absorption, fluorescence and excitation spectra as well as the fluorescence quantum yields for the compounds were measured in dibutyl ether, 1,4-dioxane, ethyl acetate and acetonitrile; fluorescence lifetimes were measured in ethyl acetate and dimethyl sulfoxide. The influences of both the character of the N-substituent and the solvent polarity upon the spectra and quantum yields are discussed.

An alternative procedure has been described for the syntheses of several bi- and trichromophoric compounds consisting of 1-aminopyrene and 3-aminobenzanthrone chromophoric subsystems connected by an s-triazinyl ring spacer. The synthetic method used, which utilises an autoclave under autogenous pressure, is suitable for the nucleophilic substitution of both chlorine atoms within the triazinyl ring by weakly basic aromatic amines. The structures of the synthesized compounds were confirmed using elemental analysis, 1H NMR, and mass spectra. UV/vis absorption and fluorescence spectra and fluorescence quantum yields were measured. The dependence of fluorescence intensity and fluorescence quantum yields on solvent polarity was investigated.

Non-substituted naphthalene sulphonic acids are strong acids, which are completely ionised in aqueous and aqueous-organic solutions. Because of repulsive electrostatic interactions, they are more or less excluded from the pores of the column packing materials commonly used in reversed-phase chromatography. The ionic exclusion can be suppressed by increasing the ionic strength of the mobile phase. In aqueous sodium sulphate solutions, very good selectivity was observed for isomeric naphthalene di- and tri-sulphonic acids, allowing reversed-phase separations of these strongly ionic compounds without addition of ion-pairing reagents to the mobile phase. The retention of the isomeric acids increases proportionally to the dipole moment, which can be explained by its effect on increasing exposure of the naphthalene ring to hydrophobic interactions with the non-polar stationary phases. Chromatographic behaviour of isomeric naphthalene di- and tri-sulphonic acids was investigated on 25 different columns for reversed-phase chromatography. The elution order of the isomers is the same on all the columns, but very strong stationary phase effects were observed on the retention and on the band asymmetry, depending on polar interactions with residual silanol groups and other polar adsorption centres in the stationary phases. These effects are independent of the organic solvents, as the tests are performed in purely aqueous mobile phases and allow classification of the columns into several groups.

The solvent dependence of absorption and fluorescence spectra, fluorescence lifetimes (τFl), and quantum yields (qFl) of various 3-substituted benzanthrone derivatives have been investigated. A consistent correlation between fluorescence quantum yield and emitting state energy has been found that holds for all 6 derivatives in 11 solvents. The experimental data together with the results of semiempirical quantum chemical calculations indicate that the main quenching channel of the fluorescent S1(π,π*) excited state is intersystem crossing to an upper (n,π*) triplet state, TN. The rate constant and efficiency of intersystem crossing between these two states are strongly influenced by the substituent and by the solvent polarity, as both modulate the singlet state energy and the S1−TN energy gap. The rate constant of direct S1 → T1 intersystem crossing is small in most systems but appears to increase with a decrease in the energy of the S1 state.

We synthesized and studied N-palmitoyl-3-aminobenzanthrone (ABA-C-15), which we proved to be an advantageous new fluorescent phospholipid membrane label. While the absorption of ABA-C-15 in protic solvents shows negative solvatochromism, its fluorescence emission is substantially red-shifted when the polarity of the solvent is increased. ABA-C15 is excitable by lasers emitting in the range between :390 and 190 nm; it exhibits reasonable quantum yields in protic solvents and binds with high affinity to small unilamellar phospholipid vesicles. Absorption, steady state fluorescence, and solvent relaxation data indicate that the aminobenzanthrone chromophore is located in the headgroup region of phospholipid bilayers in the liquid crystalline state of small unilamellar vesicles. The solvent relaxation kinetics probed by ABA-C-15 in the liquid crystalline state is characterized by three solvent relaxation times in the order of 0.05. 0.2, and 1.5 ns, respectively. We observed that the relative contribution of the 0.05 ns component and the overall Stokes shift became larger with increasing difference between the experimental temperature and the main phase transition temperature; this suggests that the chromophore becomes more accessible by water molecules. In the gel phase, a component faster than 30 ps significantly contributes to the solvent relaxation kinetics. However, the solvent relaxation on the nanosecond time seat(., appears to be slower than in the liquid crystalline phase. The shape and time evolution of the time-resolved emission spectra suggest that two distinct microenvironments of the dye might be responsible for the atypical solvent relaxation characteristics in the gel phase.

The series of dyes derived from 1-indanylidenemalononitrile were prepared and characterised. The purity of the dyes was checked by TLC and elemental analysis; the structure of substances was confirmed by 1H and 13C NMR spectra. The relationships among the structure of dyes, their absorption characteristics and the polarity of a solvent were investigated. The full optimised geometry was computed by AM1 method, the theoretical characteristics of electronic transitions were studied by PPP-MO, CNDO/S and INDO/S procedures. Due to possible application of the studied dyes in textile practice, the colouristic characteristics were determined as well.

Ultrafast time resolved fluorescence anisotropy decay measurements were performed to gain insight into the energy gap dependence of donor-acceptor inter-chromophoric coupling within one supra-molecule. Three new compounds, each consisting of two semi-rigidly linked and strongly coupled chromophores, were designed and synthesized for this study. Their general structure is donor-spacer-acceptor, where "donor" is phenylamino, pyrenylamino, or benzanthronylamino moiety, and acceptor is aminobenzanthrone. While being similar structurally, the compounds differ significantly in the excitation energy difference of the two chromophores in a supra-molecule. Experimental data show an ultrafast initial fluorescence emission anisotropy decrease (within less then 1 ps) when the excited state energies of the interacting chromophores are close to each other or equal. No such fast fluorescence anisotropy dynamics is observed for a compound with a large energy gap.