Spectral and acid-base features of 3,7-dihydroxy-2,8-diphenyl-4H,6H-pyrano[3,2-g]chromene-4,6-dione (diflavonol)--a potential probe for monitoring the properties of liquid phases

Theoretical Investigation of Excited-State Intramolecular Double-Proton Transfer Mechanism of Substituent Modified 1, 3-Bis (2-Pyridylimino)-4,7-Dihydroxyisoindole in Dichloromethane Solution

In this paper, density functional theory (DFT) and time-dependent DFT (TDDFT) methods were used to investigate substituent effects and excited-state intramolecular double-proton transfer (ESIDPT) in 1, 3-bis (2-pyridylimino)-4, 7-dihydroxyisoindole (BPI–OH) and its derivatives. The results of a systematic study of the substituent effects of electron-withdrawing groups (F, Cl and Br) on the adjacent sites of the benzene ring were used to regulate the photophysical properties of the molecules and the dynamics of the proton-transfer process. Geometric structure comparisons and infrared (IR) spectroscopic analysis confirmed that strengthening of the intramolecular hydrogen bond in the first excited state (S1) facilitated proton transfer. Functional analysis of the reduced density gradient confirmed these conclusions. Double-proton transfer in BPI–OH is considered to occur in two steps, i.e., BPI–OH (N) [Formula: see text] BPI–OH (T1) [Formula: see text] BPI–OH (T2), in the ground state (S0) and the S1 state. The potential-energy curves (PECs) for two-step proton transfer were scanned for both the S0 and S1 states to clarify the mechanisms and pathways of proton transfer. The stepwise path in which two protons are consecutively transferred has a low energy barrier and is more rational and favorable. This study shows that the presence or absence of coordinating groups, and the type of coordinating group, affect the hydrogen-bond strength. A coordinating group enhances hydrogen-bond formation, i.e., it promotes excited-state intramolecular proton transfer (ESIPT).

Single and double intramolecular proton transfers in the electronically excited state of flavone derivatives

3,7-Dihydroxyflavone derivatives containing carbonyl fragments were synthesized. Results of the fluorescent spectroscopy investigations indicate that one of them undergoes Excited State Intramolecular Double Proton Transfer (ESIDPT).

Cinnamoyl pyrones in proton-donating media: electronic structure and spectral properties of protolytic forms

Spectral properties of cinnamoyl pyrone (CP) and its derivatives were studied in water-alcohol and water solutions within a wide pH/H(0) range. It was found that the most of CP may exist in neutral, anionic and cationic forms, except for alkylamino substituted CP, which can also form dications. The constants characterizing equilibria between all the protolytic forms were obtained. CP anions appears as a result of 4-hydroxy group dissociation. It was found that the acidity of CP decreases upon the excitation, that excepts the photodissociation or intramolecular proton transfer in the excited state. The formation of cations and dications occurs by means of protonation of alkylamino group or/and exocyclic carbonyl group. The theoretical analysis of electronic structure has shown that long-wavelength electronic transitions of neutral and anionic CP forms are of interfragmental charge-transfer (ICT) character. However, in the case of anions, ICT is hindered due to their nonplanar geometrical structure. The band maxima positions in experimental absorption spectra of neutral CP and in absorption and emission spectra of cations correlate linearly with theoretical estimations of charge transfer in CP molecules. The absence of the fluorescence, characteristic for the most of neutral CP, is due to the intersystem crossing, that is proved by the appearance of the phosphorescence of non-fluorescent CP at low temperatures.

3-Hy-droxy-2-(4-hy-droxy-phen-yl)-4H-chromen-4-one

In the title compound, C₁₅H₁₀O₄, the benzene ring is twisted at an angle of 20.7 (1)° relative to the 4H-chromene skeleton. In the crystal, adjacent mol­ecules are linked via a network of O—H⋯O and C—H⋯O hydrogen bonds. The mean planes of adjacent 4H-chromene moieties are parallel or oriented at an angle of 20.9 (1)° in the crystal structure.

2-(4-Fluoro-phen-yl)-3-hy-droxy-4H-chromen-4-one

In the crystal structure of the title compound, C(15)H(9)FO(3), inversely oriented mol-ecules form inversion dimers through pairs of O-H⋯O hydrogen bonds. The benzene ring is twisted at an angle of 12.0 (1)° relative to the 4H-chromene skeleton of the mol-ecule. Adjacent 4H-chromene units are parallel in a given column or oriented at an angle of 50.0 (1)° in neighboring, inversely oriented, columns, forming a herringbone pattern.

Characterization of coupled ground state and excited state equilibria by fluorescence spectral deconvolution

Fluorescence probes with multiparametric response based on the relative variation in the intensities of several emission bands are of great general utility. An accurate interpretation of the system requires the determination of the number, positions and intensities of the spectral components. We have developed a new algorithm for spectral deconvolution that is applicable to fluorescence probes exhibiting a two-state ground-state equilibrium and a two-state excited-state reaction. Three distinct fluorescence emission bands are resolved, with a distribution of intensities that is excitation-wavelength-dependent. The deconvolution of the spectrum into individual components is based on their representation as asymmetric Siano-Metzler log-normal functions. The application of the algorithm to the solvation response of a 3-hydroxychromone (3HC) derivative that exhibits an H-bonding-dependent excited-state intramolecular proton transfer (ESIPT) reaction allowed the separation of the spectral signatures characteristic of polarity and hydrogen bonding. This example demonstrates the ability of the method to characterize two potentially uncorrelated parameters characterizing dye environment and interactions.