Relaxation process of photoexcited berberine via aggregation and dissociation state-dependent intramolecular electron transfer.

The fluorescence quantum yield of berberine in aqueous solution is significantly smaller than those of organic solution. The time profile of fluorescence intensity of berberine was analyzed by a bi-exponential function, showing that two kinds of states of berberine exist in the solutions. The observed fluorescence lifetime of shorter lifetime species of berberine in water (0.

Recognition of specific monosaccharides by fluorescence change through the suppression effect on excited-state intermolecular proton transfer reactions.

Pyrene-urea derivatives and acetate anions were used to investigate the excited-state intermolecular proton transfer (ESPT) reaction, where a molecule undergoes intermolecular proton transfer to form a tautomer species in the excited state. Since ESPT occurs when intermolecular hydrogen bonds exist between urea compounds and acetate species, we hypothesize that this reaction might be influenced by compounds with hydroxy groups. In this study, cyclodextrins, saccharides, and ethanol were examined to assess the effects of hydroxy groups on the ESPT reaction.

π-Conjugation effects on excited-state intermolecular proton-transfer reactions of anthracene-urea derivatives in the presence of acetate anions.

This study investigated emissive urea compounds with an anthryl moiety on one side and a substituent group (biphenyl, naphthyl, benzyl, or cyclohexyl) on the other side across from the urea group. This was performed to determine the contribution of π-conjugation on a substituent group to excited-state intermolecular proton-transfer (ESPT) reactions in the presence of acetate anions. Fluorescence lifetime measurements revealed that the rate constant of the ESPT reaction from the normal form to the tautomer form increased with the length of the π-conjugation.

Substituent effects of halogens on the excited-state intermolecular proton transfer reactions.

Fluorescent aromatic urea compounds undergo excited-state intermolecular proton transfer (ESPT) in the presence of acetate anions to produce an excited state of the tautomer (T*) from the excited state of the complex (N*), resulting in dual fluorescence. Herein, we performed spectroscopic measurements of anthracen-1-yl-3-phenylurea derivatives with substituents, -CF, -F, or -Cl, at the p-position of the phenyl group in the presence of acetate to investigate the substituent effects on the ESPT reaction and the deactivation processes of N* and T*. Kinetic analysis showed that the reverse ESPT rate constant (k) depended on the respective substituents, suggesting that each substituent may influence the reverse ESPT process differently.

Protein Photodamaging Activity and Photocytotoxic Effect of an Axial-Connecting Phosphorus(V)porphyrin Trimer.

An axial-connecting trimer of the porphyrin phosphorus(V) complex was synthesized to evaluate the relaxation process of the photoexcited state and the photosensitizer activity. The photoexcitation energy was localized on the central unit of the phosphorus(V)porphyrin trimer. The photoexcited state of the central unit was relaxed through a process similar to that of the monomer phosphorus(V)porphyrin.

Time-Resolved Infrared Spectroscopy with Multivariate Analysis on Photoinduced Proton Transfer in Aromatic Urea-Acetate Anion Complexes.

1-Anthracen-2-yl-3-phenylurea (2PUA) is an aromatic urea compound, which forms a hydrogen-bonded complex with an acetate anion (AcO), 2PUA-AcO complex. We investigated the photoinduced reaction of the 2PUA-AcO complex in dimethyl sulfoxide (DMSO) by nanosecond time-resolved infrared (TR-IR) spectroscopy. TR-IR spectra obtained after the photoexcitation of 2PUA with the equal concentration of AcO were consistently explained by a photoinduced proton transfer model.

Opposite substituent effects in the ground and excited states on the acidity of N-H fragments involved in proton transfer reaction in aromatic urea compounds.

To investigate substitution effects on excited-state intermolecular proton transfer (ESPT) reactions as well as acidity of proton donating fragments in the ground state, we synthesized substituted anthracen-2-yl-3-phenylurea derivatives that form a hydrogen bonds with acetate anions and undergo ESPT reaction. Fluorescence lifetime measurements and their kinetic analyses revealed that the trifluoromethyl group on the phenyl ring as an electron-withdrawing group caused a slow ESPT reaction despite an increase in the acidity of the N-H fragment in the ground state. In contrast, the methoxy group as a donating group leads to a fast ESPT reaction despite a reduction of the acidity of the N-H fragment in the ground state.

Effect of Moderate Hydrogen Bonding on Tautomer Formation via Excited-State Intermolecular Proton-Transfer Reactions in an Aromatic Urea Compound with a Steric Base.

1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU), which forms weak hydrogen bonds despite the high basicity caused by its hindered structure, was used to investigate tautomer formation via excited-state intermolecular proton-transfer (ESPT) reactions.

A Dual Emissive Coumarin-urea Derivative with an Electron-withdrawing Substituent in the Presence of Acetate Anion.

We investigated the fluorescent properties, including the excited-state intermolecular proton transfer, of urea derivatives comprising a coumarin ring, which is a widely used fluorophore. We prepared two different coumarin-urea derivatives, 6CU and 7CU, which bear a urea-based substituent at the 6 and 7 positions of a coumarin ring, respectively. In the presence of the acetate ion, 7CU showed additional tautomer fluorescence emission with respect to 6CU, indicating that tautomer formation depends on the positions of the urea-based substituent on the coumarin ring.

Photochemical generation of the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical from caged nitroxides by near-infrared two-photon irradiation and its cytocidal effect on lung cancer cells.

Novel caged nitroxides (nitroxide donors) with near-infrared two-photon (TP) responsive character, 2,2,6,6-tetramethyl-1-(1-(2-(4-nitrophenyl)benzofuran-6-yl)ethoxy)piperidine () and its regioisomer , were designed and synthesized. The one-photon (OP) (365 ± 10 nm) and TP (710-760 nm) triggered release (i.e.

Kinetic analysis of tautomer forms of aromatic-urea compounds with acetate ions: solvent effect of excited state intermolecular proton transfer.

In this paper, we report the solvent effect of excited state intermolecular proton transfer (ESIPT) reactions of urea compounds in the presence of tetrabutylammonium acetate (TBAAc). We prepared anthracene-urea compounds (9An and 2An), a pyrene-urea compound (Py) and an anthracene-diurea compound (9,10An), which have alkylsulfonyl groups to improve their solubility in various organic solvents. We investigated the solvent effects of the ESIPT reaction using absorption, fluorescence, and 1H NMR spectroscopy along with fluorescence decay measurements in dimethyl sulfoxide (DMSO), acetonitrile (MeCN), tetrahydrofuran (THF) and toluene.

Multi-molecular emission of a cationic Pt(ii) complex through hydrogen bonding interactions.

The cationic Pt complexes with amide groups have been found to show dimer emission through hydrogen bonding interactions with counter anions even at low concentration. In order to investigate further details of dimer emission, we prepared three Pt complexes, Pt·B(CF), Pt·Cl, and Pt·PF, whose counter anions possess different strengths of a hydrogen bonding acceptor. Hydrogen bonding interactions in the ground state and excited-state dynamics of the Pt complexes were evaluated by NMR analysis, temperature dependence, and kinetics of dimer emission.

Excited-state intermolecular proton transfer dependent on the substitution pattern of anthracene-diurea compounds involved in fluorescent ON-OFF-ON response by the addition of acetate ions.

We report anthracene-diurea compounds which behave as anion sensors based on the fluorescence emission regulated by the substitution position on the anthracene ring. Anthracene-diurea compounds exhibit different excited-state intermolecular proton transfer (ESIPT) reactions depending on the pattern of the substituents. Three new anthracene-diurea compounds that have two phenylurea groups substituted at different positions on anthracene were synthesized.

Modulation of the Emission Mode of a Pt(II) Complex via Intermolecular Interactions.

Compounds with controllable color emissions are potentially useful as photoluminescent materials in imaging and sensing applications. Multimolecular emission can be used realizing variable-color emitters and has been demonstrated in the solid state. However, achieving multimolecular emission in solution is difficult to control.

Fluorescence Sensor with A New ON -OFF-ON Switching Mechanism Using the Excited State Intermolecular Proton Transfer Reaction of An Anthracene-diurea Compound.

A new photoreaction mechanism of "Three-state molecular switch" fluorescence sensor based on ON -OFF-ON sequence was achieved by anthracene-diurea compound, which was designed using two phenylurea groups and one anthracene, 9,10BtDSPUA. Photochemical properties of 9,10BtDSPUA and interaction between 9,10BtDSPUA and anion were investigated in detail by absorption, H NMR, fluorescence, and fluorescence decay measurements. While the fluorescence of 9,10BtDSPUA in DMSO (ON ) was quenched in the presence of low concentration of acetate anion (OFF), fluorescence enhancement occurred by the addition of high concentration of acetate anion (ON ).

Control of the intermolecular photodimerization of anthracene derivatives by hydrogen bonding of urea groups in dilute solution.

The photodimerization reaction of anthracene derivatives was performed by capitalizing on intermolecular hydrogen bonds. Anthracene derivatives that can control the dimerization reaction depending on the substitution site were designed by using two anthryl moieties and one urea group, referred to as N,N'-dianthracen-n-ylurea, nDAU (n = 1, 2 and 9), which are symmetrically substituted by 1-anthryl, 2-anthryl and 9-anthryl groups, respectively. We investigated the excimer emission and photodimerization reaction of these anthracene-urea derivatives using absorption, emission, and (1)H NMR spectroscopy along with fluorescence decay measurements.

Producing a dual-fluorescent molecule by tuning the energetics of excited-state intramolecular proton transfer.

We report herein the selective preparation of normal, tautomeric, and dual-fluorescent molecules with a common ESIPT core. 2'-Hydroxyacetophenone (OHAP) is known as a typical molecule that undergoes excited-state intramolecular hydrogen transfer (ESIPT) to display fluorescence emission from the excited state of the tautomer. In this study, a series of ten OHAP-cored fluorescent molecules were prepared and their excited state properties have been explored.

Determination of Singlet Oxygen and Electron Transfer Mediated Mechanisms of Photosensitized Protein Damage by Phosphorus(V)porphyrins.

The mechanism of photosensitized protein damage byphosphorus(V) tetraphenylporphyrin derivatives (P(V)TPPs) wasquantitatively clarified. P(V)TPPs bound to human serum albumin(HSA), a water-soluble protein, and damaged its tryptophan residueduring photoirradiation. P(V)TPPs photosensitized singlet oxygen ((1)O(2))generation, and the contribution of (1)O(2) to HSA damage was confirmedby the inhibitory effect of sodium azide, a (1)O(2) quencher.

Red/near-infrared luminescence tuning of group-14 element complexes of dipyrrins based on a central atom.

A dipyrrin complex has been one of the most utilized fluorescent dyes, and a variety of dipyrrin complexes show intriguing functions based on the various coordination structures of the central element. We now report the synthesis, structure, and photophysical properties of germanium and stannane complexes of the N2O2-type tetradentate dipyrrin, L·Ge and L·Sn, which are heavier analogues of the previously reported dipyrrin silicon complex, L·Si. The central group-14 atoms of the monomeric complexes have geometries close to trigonal bipyramidal (TBP), in which the contribution of the square-pyramidal (SP) character becomes higher as the central atom is heavier.

Singlet oxygen generating activity of an electron donor connecting porphyrin photosensitizer can be controlled by DNA.

To control the activity of singlet oxygen ((1)O2) generation by photosensitizer through interaction with DNA, the electron- donor-connecting water-soluble porphyrin, meso-(9-anthryl)tris(N-methyl-p-pyridinio)porphyrin (AnTMPyP), was designed and synthesized. Molecular orbital calculation speculated that the photoexcited state of AnTMPyP can be deactivated via intramolecular electron transfer from the anthracene moiety to the porphyrin moiety, forming a charge-transfer (CT) state. The electrostatic interaction between the cationic porphyrin and anionic DNA predicts a rise in the CT state energy, leading to the inhibition of the electron transfer quenching.

Photosensitized protein damage by dimethoxyphosphorus(V) tetraphenylporphyrin.

For the purpose of the basic study of photodynamic therapy, the activity of the water-soluble P(V)porphyrin, dimethoxyP(V)tetraphenylporphyrin chloride (DMP(V)TPP), on photosensitized protein damage was examined. The quantum yield of singlet oxygen generation by DMP(V)TPP (0.64) was comparable with that of typical porphyrin photosensitizers.

Dynamics of singlet oxygen generation by DNA-binding photosensitizers.

The dynamics of photosensitized singlet oxygen generation in a DNA microenvironment were examined using the DNA-binding photosensitizers berberine and palmatine. These photosensitizers generate singlet oxygen only under interaction with DNA because the singlet excited state deactivates rapidly in a nonbinding environment. A kinetic study demonstrated the reaction process whereby singlet oxygen is generated through energy transfer from the triplet excited state of DNA-binding berberine (or palmatine) to molecular oxygen.

Unusually efficient trans-to-cis photoisomerization of diphenylbutadiene dendrimers in water.

A diphenylbutadiene-cored dendrimer exhibited a remarkably high quantum yield for trans-to-cis photoisomerization in aqueous solution. Analysis of the fluorescence lifetimes and the wavelength-dependent excitation spectra suggested that the core butadiene adopts multiple conformations, one or several of which is sufficiently distorted to undergo preferential photoisomerization.

Extremely efficient and long lifetime fluorescence of cis-stilbene contained in a rigid dendrimer.

The fluorescence quantum yield of cis-stilbene-cored rigid polyphenylene dendrimer (cis-G2) is 20% even at room temperature. Moreover, the fluorescence lifetime of cis-G2 is twice as long as that of the corresponding trans-isomer.

Kinetics of hydrogen bonding between anthracene urea derivatives and anions in the excited state.

Urea compounds are useful anion sensors due to their hydrogen-bonding capabilities. We investigated the emissive properties of complexes consisting of urea-anthracene (nPUA, n = 1, 2) host compounds and acetate anions held as guests through intermolecular hydrogen bonding. The kinetics of a new emission band formed by conformational changes in the excited singlet state were revealed.