9-Borafluoren-9-yl and diphenylboron tetracoordinate complexes of F- and Cl-substituted 8-quinolinolato ligands: synthesis, molecular and electronic structures, fluorescence and application in OLED devices.

Six new four-coordinate tetrahedral boron complexes, containing 9-borafluoren-9-yl and diphenylboron cores attached to orthogonal fluorine- and chlorine-substituted 8-quinolinolato ligand chromophores, have been synthesised, characterised, and applied as emitters in organic light-emitting diodes (OLEDs). An extensive steady-state and time-resolved photophysical study, in solution and in the solid state, resulted in the first-time report of delayed fluorescence (DF) in solid films of 8-quinolinolato boron complexes. The DF intensity dependence on excitation dose suggests that this emission originates from triplet-triplet annihilation (TTA).

Luminescent halogen-substituted 2-(N-arylimino)pyrrolyl boron complexes: the internal heavy-atom effect.

A group of new boron complexes [BPh{κN,N'-NCH-2-C(H)[double bond, length as m-dash]N-CHX}] (X = 4-Cl 4c, 4-Br 4d, 4-I 4e, 3-Br 4f, 2-Br 4g, 2-I 4h) containing different halogens as substituents in the N-aryl ring have been synthesized and characterized in terms of their molecular properties. Their photophysical characteristics have been thoroughly studied in order to understand whether these complexes exhibit an internal heavy-atom effect. Phosphorescence emission was found for some of the synthesized halogen-substituted boron molecules, particularly for 4g and 4h.

Ground and excited state properties of furanoflavylium derivatives.

The comparison of the ground-state reactivity of anthocyanins and aurone model compounds (i.e. with and without the furano bridge) has shown that the kinetic paradigm does not depend on the bridge but only on the hydroxyl substituent pattern, independently of the presence of the bridge: (i) bell shaped kinetics for those with two hydroxyl substituents in position 4' and 7, and (ii) four distinct kinetic steps for the mono substituted compounds with a hydroxyl in position 4'.

Boron complexes of aromatic 5-substituted iminopyrrolyl ligands: synthesis, structure, and luminescence properties.

A group of new mononuclear boron chelate compounds [BPh{κN,N'-5-R-NCH-2-C(H)[double bond, length as m-dash]N-Ar}] (R = Ar = CH7; R = CH, Ar = 2,6-iPrCH8; R = Anthracen-9-yl (Anthr), Ar = CH9; R = Anthr, Ar = 2,6-iPrCH10) were synthesized via the reaction of B(CH) with the corresponding 5-substituted 2-(N-arylformimino)pyrrole ligand precursors 3-6. These complexes were prepared in order to evaluate the luminescence potential derived from the substitution of the position 5 of the pyrrolyl ring with an aromatic group. Compounds 7-10 were photophysically characterized in solution and in the solid state.

Ground- and Excited-State Acidity of Analogs of Red Wine Pyranoanthocyanins.

Pyranoflavylium cations are synthetic analogs containing the same basic chromophore as the pyranoanthocyanins that form in red wine during maturation and are responsible for its final color. Determination of the ground- and excited-state acidities for a series of eight substituted hydroxy pyranoflavylium cations shows that they are weak acids in the ground state (pK ranging from 3.4 to 4.

Fluorescence Enhancement of a Cationic Fluorene-Phenylene Conjugated Polyelectrolyte Induced by Nonionic n-Alkyl Polyoxyethylene Surfactants.

The modulation of conjugated polyelectrolyte fluorescence response by nonionic surfactants is dependent on the structures of the surfactant and polymer, polymer average molecular weight, and polyelectrolyte-surfactant interactions. In this paper, we study the effect of nonionic n-alkyl polyoxyethylene surfactants (CE) with different alkyl chain lengths (CE with i = 6, 8, 10, and 12) and number of oxyethylene groups (CE with j = 5, 7, and 9) on the photophysics and ionic conductivity of poly{[9,9-bis(6'-N,N,N-trimethylammonium)-hexyl]-2,7-fluorene-alt-1,4-phenylene}bromide (HTMA-PFP) in dimethyl sulfoxide-water 4% (v/v). Molecular dynamics simulations show that HTMA-PFP chains tend to approach as the simulation evolves.

Boron complexes of aromatic ring fused iminopyrrolyl ligands: synthesis, structure, and luminescence properties.

The condensation reactions of 2-formylindole (1) or 2-formylphenanthro[9,10-c]pyrrole (2) with various aromatic amines afforded the corresponding phenyl or phenanthrene ring fused mono-/bis-iminopyrrole ligand precursors 3-8, which, upon reaction with BPh in an appropriate molar ratio, led to the new mono- and diboron chelate compounds PhB[NCHC(H)[double bond, length as m-dash]N-2,6-Ar] (Ar = 2,6-iPrCH9; CH10), PhB[(NCHC(H)[double bond, length as m-dash]N)-1,4-CH]BPh11, PhB(NCHC(H)[double bond, length as m-dash]N-Ar) (Ar = 2,6-iPrCH12; CH13), and PhB[(NCHC(H)[double bond, length as m-dash]N)-1,4-CH]BPh14, respectively. Boron complexes 12-14, containing a phenanthrene fragment fused to the pyrrolyl C3-C4 bond, are highly fluorescent in solution, with quantum efficiencies of 37%, 61% and 58% (in THF), respectively, their emission colours ranging from blue to orange depending on the extension of π-conjugation. Complexes 9-11, containing a benzene fragment fused to the pyrrolyl C4-C5 bond, are much weaker emitters, exhibiting quantum efficiencies of 10%, 7% and 6%, respectively.

Earliest events in α-synuclein fibrillation probed with the fluorescence of intrinsic tyrosines.

The fluorescence of the four tyrosines of α-synuclein (Syn) was used for probing the earliest events preceding the fibrillation of Syn, during the onset of the so-called lag-time of fibrillation. Steady-state fluorescence experiments revealed an increase in the fluorescence intensity (FI) for Syn solutions at pH values 3 and 2, in comparison with pH7, and fluorescence decays indicated that the FI increase did not result from suppression of excited-state proton transfer from the tyrosines to aspartates and glutamates, exposure of tyrosines to more hydrophobic environments, or reduction of homo-energy transfer. Instead, the FI increase was due to changes in the population of the tyrosine rotamers at low pH values.

Luminescent Di- and Trinuclear Boron Complexes Based on Aromatic Iminopyrrolyl Spacer Ligands: Synthesis, Characterization, and Application in OLEDs.

New bis- and tris(iminopyrrole)-functionalized linear (1,2-(HNC4 H3 -C(H)N)2 -C6 H4 (2), 1,3-(HNC4 H3 -C(H)N)2 -C6 H4 (3), 1,4-(HNC4 H3 -C(H)N)2 -C6 H4 (4), 4,4'-(HNC4 H3 -C(H)N)2 -(C6 H4 -C6 H4 ) (5), 1,5-(HNC4 H3 C-(H)N)2 -C10 H6 (6), 2,6-(HNC4 H3 C-(H)N)2 -C10 H6 (7), 2,6-(HNC4 H3 C-(H)N)2 -C14 H8 (8)) and star-shaped (1,3,5-(HNC4 H3 -C(H)N-1,4-C6 H4 )3 -C6 H3 (9)) π-conjugated molecules were synthesized by the condensation reactions of 2-formylpyrrole (1) with several aromatic di- and triamines. The corresponding linear diboron chelate complexes (Ph2 B[1,3-bis(iminopyrrolyl)-phenyl]BPh2 (10), Ph2 B[1,4-bis(iminopyrrolyl)-phenyl]BPh2 (11), Ph2 B[4,4'-bis(iminopyrrolyl)-biphenyl]BPh2 (12), Ph2 B[1,5-bis(iminopyrrolyl)-naphthyl]BPh2 (13), Ph2 B[2,6-bis(iminopyrrolyl)-naphthyl]BPh2 (14), Ph2 B[2,6-bis(iminopyrrolyl)-anthracenyl]BPh2 (15)) and the star-shaped triboron complex ([4',4'',4'''-tris(iminopyrrolyl)-1,3,5-triphenylbenzene](BPh2 )3 (16)) were obtained in moderate to good yields, by the treatment of 3-9 with B(C6 H5 )3 . The ligand precursors are non-emissive, whereas most of their boron complexes are highly fluorescent; their emission color depends on the π-conjugation length.

Effect of water content on the acid-base equilibrium of cyanidin-3-glucoside.

Laser Flash Photolysis was employed to measure the deprotonation and reprotonation rate constants of cyanidin 3-monoglucoside (kuromanin) in water/methanol mixtures. It was found that the deprotonation rate constant kd decreases with decreasing water content, reflecting the lack of free water molecules around kuromanin, which may accommodate and stabilize the outgoing protons. On the other hand, the reprotonation rate constant, kp, increases with the decrease in water concentration from a value of kp = 2 × 10(10) l mol(-1) s(-1) in water up to kp = 6 × 10(10) l mol(-1) s(-1) at 5.

Unveiling the Eigen-Weller ion pair from the excited state proton transfer kinetics of 3-chloro-4-methyl-7-hydroxycoumarin.

The prototropic reactions of the first excited singlet state of 3-chloro-4-methylumbelliferone (3Cl4MU), in dioxane:water mixtures (Dx:H2O), were revisited using ps-time-resolved fluorescence techniques. The data response to the dielectric constant of the mixtures revealed the presence of an additional fourth kinetic species, kinetically coupled to the neutral (N*), the tautomeric (T*), and anionic (A(-)*) forms of 3Cl4MU, which is assigned to the elusive geminate (A(-)*···H(+)) ion pair. From the data analysis, all rate constants of the prototropic and diffusion processes involved were separately evaluated.

Femtosecond and temperature-dependent picosecond dynamics of ultrafast excited-state proton transfer in water-dioxane mixtures.

Synthetic flavylium salts like the 7-hydroxy-4-methylflavylium (HMF) cation have been used as prototypes to study the chemistry and photochemistry of anthocyanins, the major group of water-soluble pigments in the plant kingdom. In this work, a combination of fluorescence upconversion with femtosecond time resolution and time-correlated single photon counting (TCSPC) with picosecond time resolution have been employed to investigate in details the excited-state proton transfer (ESPT) of HMF in water and in binary water/1,4-dioxane mixtures. TCSPC measurements as a function of temperature provide activation parameters for all of the individual rate constants involved in the proton transfer, including those for dissociation and recombination of the geminate excited base-proton pair (A*···H(+)) that can be detected in the water/dioxane mixtures (but not in water).

Tunable fluorophores based on 2-(N-arylimino)pyrrolyl chelates of diphenylboron: synthesis, structure, photophysical characterization, and application in OLEDs.

Reactions of 2-(N-arylimino)pyrroles (HNC4H3C(H)=N-Ar) with triphenylboron (BPh3) in boiling toluene afford the respective highly emissive N,N'-boron chelate complexes, [BPh2 {κ(2)N,N'-NC4H3C(H)=N-Ar}] (Ar=C6H5 (12), 2,6-Me2-C6H3 (13), 2,6-iPr2-C6H3 (14), 4-OMe-C6H4 (15), 3,4-Me2-C6 H3 (16), 4-F-C6H4 (17), 4-NO2-C6H4 (18), 4-CN-C6H4 (19), 3,4,5-F3-C6H2 (20), and C6F5 (21)) in moderate to high yields. The photophysical properties of these new boron complexes largely depend on the substituents present on the aryl rings of their N-arylimino moieties. The complexes bearing electron-withdrawing aniline substituents 17-20 show more intense (e.

Improved analysis of excited state proton transfer kinetics by the combination of standard and convolution methods.

We wish to report a powerful methodology for analysis and interpretation of complex fluorescence decays and other kinetic data, based on the addition of convolution analysis to standard (individual and global) analysis. The method was applied to cases involving excited state proton transfer of flavylium salts in water, in water-1,4-dioxane mixtures and in micellar solutions of sodium dodecyl sulfate (SDS). The results clearly support the proposal of the intermediacy of a proton-base geminate pair in environments other than water.

Model for conformational relaxation of flexible conjugated polymers: application to p-phenylenevinylene trimers in nonpolar solvents.

Photoexcitation of flexible conjugated polymers is invariably followed by a fast conformational/torsional relaxation towards a configuration favouring coplanarity of the conjugated segments. In general, the experimental relaxation rate constant (k(CR)) depends on the solvent viscosity (η) and temperature (T), and is not proportional to T/η. A theory capable of explaining the observed dependence of k(CR) on T and η over a wide range of these variables is not available.

Photophysical properties of iminopyrrolyl boron complexes: a DFT interpretation.

The three compounds [BPh(2)(κ(2)N,N'-NC(4)H(3)C(H)=N-C(6)H(5))] (A), [BPh(2)(κ(2)N,N'-NC(4)H(3)C(H)=N-1,4-C(6)H(4)-N=H)C-H(3)C(4)N-N,N'κ(2))BPh(2)] (B) and [BPh(2)(κ(2)N,N'-NC(4)H(3)C(H)=N-4,4'-C(6)H(4)-C(6)H(4)-N=(H)C-H(3)C(4)N-N,N'κ(2))BPh(2)] (C) are blue to green light emitters with average to excellent quantum yields. DFT and TD-DFT calculations were performed in order to understand their behaviour. The geometry of their ground and singlet excited state was optimised, and their absorption patterns and emission were calculated.

Syntheses and photophysical properties of new iminopyrrolyl boron complexes and their application in efficient single-layer non-doped OLEDs prepared by spin coating.

Efficient non-doped OLEDs have been achieved using new binuclear tetracoordinate organoboron complexes containing 2-(N-aryl)formiminopyrrolyl ligands.

Photoprotection and the photophysics of acylated anthocyanins.

The proposed role of anthocyanins in protecting plants against excess solar radiation is consistent with the occurrence of ultrafast (5-25 ps) excited-state proton transfer as the major de-excitation pathway of these molecules. However, because natural anthocyanins absorb mainly in the visible region of the spectra, with only a narrow absorption band in the UV-B region, this highly efficient deactivation mechanism would essentially only protect the plant from visible light. On the other hand, ground-state charge-transfer complexes of anthocyanins with naturally occurring electron-donor co-pigments, such as hydroxylated flavones, flavonoids, and hydroxycinnamic or benzoic acids, do exhibit high UV-B absorptivities that complement that of the anthocyanins.

Excited-state dynamics and self-organization of poly(3-hexylthiophene) (P3HT) in solution and thin films.

The fluorescence decays of a stereoregular head-to-tail RR-HT poly(3-hexylthiophene), P3HT, in methylcyclohexane (MCH) are described by sums of three or four exponential terms, respectively above and below -10 °C. In the high-temperature region, the polymer lifetime (ca. 500 ps) is accompanied by two shorter decay times (ca.

Picosecond dynamics of proton transfer of a 7-hydroxyflavylium salt in aqueous-organic solvent mixtures.

The intermediacy of the geminate base-proton pair (A*···H(+)) in excited-state proton-transfer (ESPT) reactions (two-step mechanism) has been investigated employing the synthetic flavylium salt 7-hydroxy-4-methyl-flavylium chloride (HMF). In aqueous solution, the ESPT mechanism involves solely the excited acid AH(+)* and base A* forms of HMF as indicated by the fluorescence spectra and double-exponential fluorescence decays (two species, two decay times). However, upon addition of either 1,4-dioxane or 1,2-propylene glycol, the decays become triple-exponential with a term consistent with the presence of the geminate base-proton pair A*···H(+).

Characterization of the singlet and triplet excited states of 3-chloro-4-methylumbelliferone.

An extensive photophysical characterization of 3-chloro-4-methylumbelliferone (3Cl4MU) in the ground-state, S(0), first excited singlet state, S(1), and lowest triplet state, T(1), was undertaken in water, neutral ethanol, acidified ethanol, and basified ethanol. Quantitative measurements of quantum yields (fluorescence, phosphorescence, intersystem crossing, internal conversion, and singlet oxygen formation) together with lifetimes were obtained at room and low temperature in water, dioxane/water mixtures, and alcohols. The different transient species were assigned and a general kinetic scheme is presented, summarizing the excited-state multiequilibria of 3Cl4MU.

Viscosity dependence of intramolecular excimer formation with 1,5-bis(1-pyrenylcarboxy)pentane in alkane solvents as a function of temperature.

Intramolecular excimer formation with 1,5-bis(1-pyrenylcarboxy)pentane, (1PC(5)1PC) is studied as a function of temperature in a series of alkane solvents and in toluene, covering a wide range of solvent viscosities η, from 0.2 to 125 cP. The rate constant k(a) of the monomer → excimer reaction is determined from the effectively single exponential monomer fluorescence decays.

Thermal unfolding kinetics of ubiquitin in the microsecond-to-second time range probed by Tyr-59 fluorescence.

Thermal folding/unfolding kinetics of wild-type ubiquitin (wt-UBQ) was studied in a wide time range, from microseconds to seconds, by combining rapid-mixing T-jump and laser T-jump with fluorescence detection (MTJ-F and LTJ-F, respectively) to monitor the fluorescence changes of Tyr-59 located on the 310-helix. The kinetics occurs exclusively in the millisecond to second time range, and the decays are strictly single exponential. From global analysis of folding and unfolding decays, the kf and ku values were determined, without use of the equilibrium constant Ku.

How to change the aggregation in the DNA/surfactant/cationic conjugated polyelectrolyte system through the order of component addition: anionic versus neutral surfactants.

The competitive interaction has been studied between double-stranded DNA (dsDNA), the cationic conjugated polyelectrolyte (CPE) poly[9,9-bis(6-N,N,N-trimethylamonium)hexyl)-fluorene-phenylene)] bromide (HTMA-PFP) and anionic or neutral surfactants (sodium dodecyl sulfonate, SDSu, and n-dodecyl pentaoxyethylene glycol ether, C(12)E(5)) in 4% (v/v) dimethyl sulfoxide (DMSO)-water using UV/visible absorption and fluorescence spectroscopy. Dramatic changes are observed in the spectroscopic behavior of the system depending on the order of addition of the reagents, the surfactant charge, and concentration range. If the neutral C(12)E(5) is added to the HTMA-PFP/dsDNA complex, no significant spectroscopic changes are observed.

Picosecond dynamics of the prototropic reactions of 7-hydroxyflavylium photoacids anchored at an anionic micellar surface.

Three water-insoluble, micelle-anchored flavylium salts, 7-hydroxy-3-octyl-flavylium chloride, 4'-hexyl-7-hydroxyflavylium chloride, and 6-hexyl-7-hydroxy-4-methyl-flavylium chloride, have been employed to probe excited-state prototropic reactions in micellar sodium dodecyl sulfate (SDS). In SDS micelles, the fluorescence decays of these three flavylium salts are tetraexponential functions in the pH range from 1.0 to 4.