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Intramolecular Proton Transfer (intramolecular + proton_transfer)
Kinds of Intramolecular Proton Transfer Selected AbstractsExcited State Intramolecular Proton Transfer of New Diphenyl- ethylene Derivatives Bearing Imino Group: A Combination of Experimental and Theoretical InvestigationCHINESE JOURNAL OF CHEMISTRY, Issue 7 2010Fang Gao Abstract In this paper, we described the synthesis and characterization of new diphenylethylene bearing imino group. We concentrated particularly on the investigation of the possibility of the excited state intramolecular charge transfer (ESIPT) of the new dyes experimentally and theoretically. The absorption and fluorescence spectroscopy of the dyes were determined in various solvents. The results showed that the maximal absorption wavelength of 2-[(4,- N,N -dimethylamino-diphenylethylene-4-ylimino)methyl]phenol (C1) and 4-[(4,- N,N -dimethylamino-diphenylethylene-4-ylimino)methyl]phenol (C2) exhibited almost independence on the solvent polarity. While as contrast, the maximal fluorescence wavelength of the dyes showed somewhat dependence on the solvent polarity. In particular, C1 displayed well-separated dual fluorescence spectroscopy. The second fluorescence peak was characterized with an "abnormal" fluorescence emission wavelength in aprotic solvents with large Stokes shift (ca. 140 nm in THF), which was much more than normal Stokes shift (ca. 30 nm in THF). This emission spectroscopy could be assigned to ESIPT emission. On the other hand, the ESIPT fluorescence of C1 was much reduced or lost in the protic solvents. While, only normal fluorescence emission was detected in various solvents. Although the absorption maxima of C1 exhibited about 10 nm red-shift with respect to those of C2, the normal fluorescence maxima of C1 and C2 were almost identical in various solvents. These results suggested that C1 could undergo ESIPT, but C2 was not able to proceed ESIPT. The molecular geometry optimization of phototautomers in the ground electronic state (S0) was carried out with HF method (Hartree-Fock) and at DFT level (Density Functional Theory) using B3LYP both, while the CIS was employed to optimize the geometries of the first singlet excited state (S1) of the phototautomers of C1 and C2 respectively. The properties of the ground state and the excited state of the phototautomers of C1 and C2, including the geometrical parameter, the energy, the frontier orbits, the Mulliken charge and the dipole moment change were performed and compared completely. The data were analyzed further based on our experimental results. Furthermore, the absorption and fluorescence spectra were calculated in theory and compared with the measured ones. The rate constant of internal proton transfer (9.831×1011 s,1) of C1 was much lower than that of salicylidene methylamine (C3, 2.045×1015 s,1), which was a typical Schiff base compound and was well demonstrated to undergo ESIPT easily under photoexcitation. [source] Photoinduced Excited State Intramolecular Proton Transfer of New Schiff Base Derivatives with Extended Conjugated Chromophores: A Comprehensive Theoretical SurveyCHINESE JOURNAL OF CHEMISTRY, Issue 6 2010Qi Wang Abstract This paper presented comprehensive theoretical investigation of excited state intramolecular proton transfer (ESIPT) of four new large Schiff base derivatives with extended conjugated chromophores. The properties of the ground state and the excited state of phototautomers of C1 to C4 [C1: 2-(4,-nitro-stilbene-4-ylimino)methylphenol; C2: 2-(4,-cyano-stilbene-4-ylimino)methylphenol; C3: 2-(4,-methoxyl-stilbene-4-ylimino)methylphenol; C4: 2-(4,- N,N -diethylamino-stilbene-4-ylimino)methylphenol], which included geometrical parameter, energy, rate constant, frontier orbit, Mulliken charge, dipole moment change, were studied by DFT (density functional theory), CIS (configuration interaction singles-excitation), TDDFT (time-dependent DFT) methods to analyze the effects of chromophore part on the occurrence of ESIPT and the role of substituent groups. The structural parameter calculation showed that the shorter RHN and larger ROH from enol to enol* form, and less twisted configuration in the excited state implied that these molecules could undergo ESIPT as excitation. Stable transition states and a low energy barrier were observed for C1 to C4. This suggested that chromophore part increased some difficulty to undergo ESIPT for these molecules, while the possibility of occurrence of ESIPT was quite high. The negative ,E* (,9.808 and ,9.163 kJ/mol) of C1 and C2 and positive ,E* (0.599 and 1.029 kJ/mol) of C3 and C4 indicated that withdrawing substituent groups were favorable for the occurrence of ESIPT. The reaction rate constants of proton transfer of these compounds were calculated in the S0 and S1 states respectively, and the high rate constants of these compounds were observed at S1 state. C1 even reached at 1.45×1015 s,1 in the excited state, which is much closed to 2.05×1015 s,1 of the parent moiety (salicylidene methylamine). Electron-donating and electron-withdrawing substituent groups had different effects on the electron density distribution of frontier orbits and Mulliken charges of the atoms, resulting in different dipole moment changes in enol*,keto* process. These differences in turn suggested that C1 and C2 had more ability to undergo ESIPT than C3 and C4. The ultraviolet/visible absorption spectra, normal fluorescence emission spectra and ESIPT fluorescence emission spectra of these compounds were predicted in theory. [source] Intramolecular proton transfer induced by divalent alkali earth metal cation in the gas stateINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2003Hongqi Ai Abstract Interactions between divalent alkali earth metal (DAEM) ions M (MBe, Mg, Ca, Sr, Ba) and the second stable glycine conformer in the gas phase, which can transfer into the ground-state glycine-M2+ (except the glycine,Be2+) among each corresponding isomers when these divalent metal ions are bound, are studied at the hybrid three-parameter B3LYP level with three different basis sets. Proton transfers from the hydroxyl to the amino nitrogen of the glycine without energy barriers have been first observed in the gas phase in these glycine,M2+ systems. The interaction between the glycine and these DAEM ions except beryllium and magnesium ion only create an amino hydrogen pointing to the original hydroxyl due to their weaker interaction relative to those divalent transition metal (DTM) ion-bound glycine derivatives, being obviously different from that between the glycine and DTM ions, in which two amino hydrogens point to the original hydroxyl oxygen when these metal-chelated glycine derivatives are produced. The interaction energy between the glycine and divalent magnesium would be the boundary of one or two amino hydrogens pointing to the hydrogyl oxygen, i.e., the ,170.3 kcal/mol of binding energy is a critical point. Similar intramolecular proton transfer has also been predicted for those DTM ion-chelated glycine systems; however, that in the gas state has not been observed in the monovalent metal ion-coordinated glycine systems. The binding energy between some monovalent TM ion and the glycine is similar to that of the glycine,Ba2+, which has the lowest binding strength among these DAEM,ion chelated glycine complexes. The difference among them only lies in the larger electrostatic and polarized effects in the latter, which favor the stability of the zwitterionic glycine form in the gas phase. According to these observations, we predict that the zwitterionic glycine would exist in the field of two positive charges in the gas phase. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 205,214, 2003 [source] Synthesis, Photophysical, and Electroluminescent Device Properties of Zn(II)-Chelated Complexes Based on Functionalized Benzothiazole DerivativesADVANCED FUNCTIONAL MATERIALS, Issue 10 2009Soo-Gyun Roh Abstract New Zn(II)-chelated complexes based on benzothiazole derivatives, including substituted functional groups such as methyl (MeZn), methoxy (MeOZn), or fluorenyl unit (FuZn), are investigated to produce white-light emission. 2-(2-Hydroxyphenyl)benzothiazole derivatives in toluene and DMSO exhibit excited-state intramolecular proton transfer (ESIPT), leading to a large Stokes shift of the fluorescence emission. However, in methanol they exhibit no ESIPT due to the intermolecular hydrogen bonding between the 2-(2-hydroxyphenyl)benzothiazole derivative and methanol. Their Zn(II)-chelated complexes exhibit the absorption band red-shifted at 500,nm in nonpolar solvent and the absorption band blue-shifted at about 420,nm in protic solvent. In multilayer electroluminescent devices, methyl-substituted Zn(II)-chelated complex (MeZn) exhibits excellent power efficiency and fluorene-substituted Zn(II)-chelated complex (FuZn) has a high luminance efficiency (1,cd,m,2 at 3.5,V, 10,400,cd,m,2 at 14,V). The EL spectra of Zn(II)-chelated complexes based on benzothiazole derivatives exhibit broad emission bands. In addition, their electron-transport property for red,green,blue (RGB) organic light-emitting diodes (OLEDs) is systematically studied, in comparison with that of Alq3. The results demonstrate the promising potential of MeZn as an electron-transporting layer (ETL) material in preference to Alq3, which is widely used as an ETL material. [source] Photophysical and Photochemical Studies of PyridoxamineHELVETICA CHIMICA ACTA, Issue 10 2003Claudio Bueno The absorption and fluorescence emission of pyridoxamine were studied as function of pH and solvent properties. In the ground state, pyridoxamine exhibits different protonated forms in the range of pH,1.5,12. Fluorescence studies showed that the same species exist at the lowest singlet excited state but at different pH ranges. The phenol group is by ca. 8,units more acidic in the excited state than in the ground state. On the other hand, the pyridine N-atom is slightly more basic in the lowest excited state than in the ground state. Excitation spectra and emission decays in the pH range of 8,10 indicate the protonation of the pyridine N-atom by proton transfer from the amine group, in the ground and singlet excited states. Spectroscopic studies in different solvents showed that pyridoxamine in the ground or excited states exhibits intramolecular proton transfer from the pyridine N-atom to the phenol group, which is more favorable in solvents of low hydrogen-bonding capacity. The cationic form with the protonated phenolic group, which emits at shorter wavelength, is the dominant species in nonprotic solvents, but, in strong proton-donor solvents, both forms exist. The fluorescence spectra of these species exhibit blue shift in protic solvents. These shifts are well-correlated with the polarity and the H-donor ability of the solvent. [source] Intramolecular proton transfer induced by divalent alkali earth metal cation in the gas stateINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2003Hongqi Ai Abstract Interactions between divalent alkali earth metal (DAEM) ions M (MBe, Mg, Ca, Sr, Ba) and the second stable glycine conformer in the gas phase, which can transfer into the ground-state glycine-M2+ (except the glycine,Be2+) among each corresponding isomers when these divalent metal ions are bound, are studied at the hybrid three-parameter B3LYP level with three different basis sets. Proton transfers from the hydroxyl to the amino nitrogen of the glycine without energy barriers have been first observed in the gas phase in these glycine,M2+ systems. The interaction between the glycine and these DAEM ions except beryllium and magnesium ion only create an amino hydrogen pointing to the original hydroxyl due to their weaker interaction relative to those divalent transition metal (DTM) ion-bound glycine derivatives, being obviously different from that between the glycine and DTM ions, in which two amino hydrogens point to the original hydroxyl oxygen when these metal-chelated glycine derivatives are produced. The interaction energy between the glycine and divalent magnesium would be the boundary of one or two amino hydrogens pointing to the hydrogyl oxygen, i.e., the ,170.3 kcal/mol of binding energy is a critical point. Similar intramolecular proton transfer has also been predicted for those DTM ion-chelated glycine systems; however, that in the gas state has not been observed in the monovalent metal ion-coordinated glycine systems. The binding energy between some monovalent TM ion and the glycine is similar to that of the glycine,Ba2+, which has the lowest binding strength among these DAEM,ion chelated glycine complexes. The difference among them only lies in the larger electrostatic and polarized effects in the latter, which favor the stability of the zwitterionic glycine form in the gas phase. According to these observations, we predict that the zwitterionic glycine would exist in the field of two positive charges in the gas phase. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 205,214, 2003 [source] Deconvolution of femtosecond time-resolved spectroscopy data in multivariate curve resolution.JOURNAL OF CHEMOMETRICS, Issue 7-8 2010Application to the characterization of ultrafast photo-induced intramolecular proton transfer Abstract In femtosecond absorption spectroscopy, deconvolution of the measured kinetic traces is still an important issue as photochemical processes that may possess shorter characteristic times than the time resolution of the experiment are usually considered. In this work, we propose to perform deconvolution of the time-dependent concentration profiles extracted from multivariate curve resolution (MCR) applied to spectrokinetic data. The profiles are fitted with a model function including a description of the instrumental response function (IRF) of the experiment. The method combines the potential benefits of soft-modeling data analysis with the ones of hard-modeling for parameter estimation. The potential of the method is demonstrated first analyzing five synthetic data sets for which IRF of different widths are simulated. It is then successfully applied to resolve femtosecond UV-visible transient absorption spectroscopy data investigating the photodynamics of salicylidene aniline, a photochromic molecule of wide interest. Considering a time resolution of 150,fs for the IRF, a characteristic time of 45,fs is recovered for the first step of the photo-induced process which consists of an ultrafast intramolecular proton transfer. Our results also confirm the existence of an intermediate species with a characteristic time of 240,fs. Copyright © 2010 John Wiley & Sons, Ltd. [source] Syntheses and photophysical properties of some 4-arylpyridinium saltsJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 1 2001Charles J. Kelley A number of 4-arylpyridines, many methoxy substituted, were prepared by an efficient two-step method involving aryl Grignard addition to 1-methyl-4-piperidone and direct aromatization of the resulting 4-aryl-4-piperidinols. The pyridines were N -alkylated to give sulfonate salts desired for their fluorescent properties. Study of selected compounds as laser dyes revealed several structures to be efficient dyes lasing in the 530-550 nm range. Two new diazaquaterphenyls were prepared and were quaternized. These salts exhibited intense fluorescence in the 420-450 nm range, but would not lase. A phenolic azaterphenyl suitably substituted for excited state intramolecular proton transfer (ESIPT) did not fluoresce at all. [source] Synthesis of imidazole-containing conjugated polymers bearing phenol unit as side group and excited state intramolecular proton transfer-mediated fluorescenceJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 18 2009Koji Takagi Abstract Dibromobenzimidazole and dibromoimidazole bearing hydroxyl group-protected phenol unit (1 and 2) were prepared and they showed an intramolecular hydrogen bonding between ether oxygen and amino proton of imidazole. The palladium-catalyzed Suzuki coupling polymerization of 1 and 2 with benzene bis(boronic acid) derivatives gave soluble polymers (3 and 4), where the molecular weights were limited probably due to the coordination ability of imidazole to palladium metal. The phenol hydroxyl groups were subsequently deprotected using BBr3 to obtain 3, and 4,. From the 1H NMR spectra, the complete conversion to the hydroxyl group and the formation of another type of intramolecular hydrogen bonding between hydroxyl proton and imine nitrogen were confirmed. In the UV and PL spectra of 3, and 4,, the excited state intramolecular proton transfer (ESIPT) occurred to shift the emission spectra toward lower energy region compared to 3 and 4. Especially, the PL spectrum of 3, demonstrated large stokes shift (145 nm) in THF solution. The ESIPT-mediated fluorescence was influenced by the addition of methanol and trifluoroacetic acid, which inhibited the formation of intramolecular hydrogen bonding. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4822,4829, 2009 [source] Mass spectrometric characterization of 4-oxopentanoic acid and gas-phase ion fragmentation mechanisms studied using a triple quadrupole and time-of-flight analyzer hybrid system and density functional theoryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 14 2008Basem Kanawati 4-Oxopentanoic acid was characterized experimentally by electrospray ionization using a triple quadrupole and time-of-flight analyzer hybrid system. This compound was chosen as a model substance for small organic compounds bearing an acetyl and a carboxyl group. Collision-induced dissociation experiments at different activation energies were performed to elucidate possible fragmentation pathways. These pathways were also studied on the theoretical level using density functional theory (DFT) B3LYP/6-311++G(3df,3pd)//B3LYP/6-31+G(d)+ZPVE calculations. CO2 ejection from the [M,H], anion of 4-oxopentanoic acid was observed and the fragmentation pathway studied by DFT reveals a new concerted mechanism for CO2 elimination accompanied by an intramolecular proton transfer within a pentagonal transition state structure. Successive elimination of water and CO from the [M,H], anion of 4-oxopentanoic acid was also observed. A rearrangement in the primary deprotonated ketene anion produced after water elimination was found on the theoretical level and leads to CO elimination from the primary product anion [M,H,H2O],. Energy diagrams along the reaction coordinates of the fragmentation pathways are presented and discussed in detail. Mulliken charge distributions of some important structures are presented. Copyright © 2008 John Wiley & Sons, Ltd. [source] X-ray crystallographic structures of enamine and amine Schiff bases of pyridoxal and its 1:1 hydrogen-bonded complexes with benzoic acid derivatives: evidence for coupled inter- and intramolecular proton transferACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2006Shasad Sharif Crystal structures of Schiff bases containing pyridoxal (PL), N -(pyridoxylidene)-tolylamine, C15H16N2O2 (I), N -(pyridoxylidene)-methylamine, C9H12N2O2 (III), and their 1:1 adduct with 2-nitrobenzoic acid, (I)+ C7H4NO (II), and 4-nitrobenzoic acid, (III)+ C7H4NO (IV), serve as models for the coenzyme pyridoxal-5,-phosphate (PLP) in its PLP-dependent enzymes. These models allow the study of the intramolecular OHN hydrogen bond of PL/PLP Schiff bases and the H-acceptor properties of their pyridine rings. The free base (I) forms hydrogen-bonded chains involving the hydroxyl side groups and the rings of adjacent molecules, whereas (III) forms related hydrogen-bonded cyclic dimers. The adducts (II)/(IV) consist of 1:1 hydrogen-bonded complexes, exhibiting strong intermolecular bonds between the carboxylic groups of the acids and the pyridine rings of (I)/(III). In conclusion, the proton in the intramolecular O,H,N hydrogen bond of (I)/(III) is located close to oxygen (enolamine form). The added acids protonate the pyridine ring in (II)/(IV), but only in the latter case does this protonation lead to a shift of the intramolecular proton towards the nitrogen (ketoimine form). All crystallographic structures were observed in the open form. In contrast, the formation of the pyridinium salt by dissolving (IV) leads to the cyclic aminal form. [source] Efficient Intramolecular Hydroalkoxylation of Unactivated Alkenols Mediated by Recyclable Lanthanide Triflate Ionic Liquids: Scope and MechanismCHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2010Alma Dzudza Dr. Abstract Lanthanide triflate complexes of the type [Ln(OTf)3] (Ln=La, Sm, Nd, Yb, Lu) serve as effective, recyclable catalysts for the rapid intramolecular hydroalkoxylation (HO)/cyclization of primary/secondary and aliphatic/aromatic hydroxyalkenes in imidazolium-based room-temperature ionic liquids (RTILs) to yield the corresponding furan, pyran, spirobicyclic furan, spirobicyclic furan/pyran, benzofuran, and isochroman derivatives. Products are straightforwardly isolated from the catalytic solution, conversions exhibit Markovnikov regioselectivity, and turnover frequencies are as high as 47,h,1 at 120,°C. The ring-size rate dependence of the primary alkenol cyclizations is 5>6, consistent with a sterically controlled transition state. The hydroalkoxylation/cyclization rates of terminal alkenols are slightly more rapid than those of internal alkenols, which suggests modest steric demands in the cyclic transition state. Cyclization rates of aryl-functionalized hydroxyalkenes are more rapid than those of the linear alkenols, whereas five- and five/six-membered spirobicyclic skeletons are also regioselectively closed. In cyclization of primary, sterically encumbered alkenols, turnover-frequency dependence on metal-ionic radius decreases by approximately 80-fold on going from La3+ (1.160,Å) to Lu3+ (0.977,Å), presumably reflecting steric impediments along the reaction coordinate. The overall rate law for alkenol hydroalkoxylation/cyclization is v,k[catalyst]1[alkenol]1. An observed ROH/ROD kinetic isotope effect of 2.48 (9) is suggestive of a catalytic pathway that involves kinetically significant intramolecular proton transfer. The present activation parameters,enthalpy (,H,)=18.2 (9),kcal,mol,1, entropy (,S,)=,17.0 (1.4),eu, and energy (Ea)=18.2 (8),kcal,mol,1,suggest a highly organized transition state. Proton scavenging and coordinative probing results suggest that the lanthanide triflates are not simply precursors of free triflic acid. Based on the kinetic and mechanistic evidence, the proposed catalytic pathway invokes hydroxyl and olefin activation by the electron-deficient Ln3+ center, and intramolecular H+ transfer, followed by alkoxide nucleophilic attack with ring closure. [source] Luminescent Excited-State Intramolecular Proton-Transfer (ESIPT) Dyes Based on 4-Alkyne-Functionalized [2,2,-Bipyridine]-3,3,-diol DyesCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2008Gilles Ulrich Dr. Abstract Functionalized 6,6,-dimethyl-3,3,-dihydroxy-2,2,-bipyridine dyes (BP(OH)2) exhibit relatively intense fluorescence from the relaxed excited state formed by excited-state intramolecular proton transfer (ESIPT). Bromo functionalization of (BP(OH)2) species followed by palladium(0)-catalyzed reactions allows the connection (via alkyne tethers) of functional groups, such as the singlet-emitter diazaboraindacene (bodipy) group or a chelating module (terpyridine; terpy). The X-ray structure of the terpy-based compound confirms the planarity of the 3,3,-dihydroxy-bipyridine unit. The new dyes exhibit relatively intense emission on the nanosecond timescale when in fluid solution, in the solid state at 298,K, and in rigid glasses at 77,K. In some cases, the excitation wavelength luminescence was observed and attributed to 1),inefficiency of the ESIPT process in particular compounds when not enough vibrational energy is introduced in the Franck,Condon state, which is populated by direct light excitation or 2),the presence of an additional excited state that deactivates to the ground state without undergoing the ESIPT process. For some selected species, the effect of the addition of zinc salts on the absorption and luminescence spectra was investigated. In particular, significant fluorescence changes were observed as a consequence of probable consecutive formation of a 1:1 and 1:2 molecular ratio of ligand/zinc adducts owing to coordination of ZnII ions by the bipyridyldiol moieties, except when an additional terpyridine subunit is present. In fact, this latter species preferentially coordinates to the ZnII ion in a 1:1 molecular ratio and further inhibits ZnII interaction. In the hybrid Bodipy/BP(OH)2 species, complete energy transfer from the BP(OH)2 to the bodipy fluorophore occurs, leading to exclusive emission from the lowest-lying bodipy subunit. Des composés colorés à base de 6,6,-dimethyl-3,3,-dihydroxy-2,2,-bipyridine (BP(OH)2) ont été synthétisés et présentent une fluorescence relativement intense issue de la relaxation d,un état excité provenant d,un transfert de proton dans l,état excité (ESIPT). La bromation de dérivés (BP(OH)2) suivie d,un couplage croisé catalysé par du Pd0sous-ligandé permet de connecter (par l,intermédiaire de pont alcyne) des groupes fonctionnels comme un groupe émetteur singulet de type boradiazaindacène (Bodipy) ou un module chélatant universel (une terpyridine). Une structure par diffraction aux rayons X a été obtenu avec le dérivé terpyridine, celle ci confirme la planéité de l,unité 3,3,-dihydroxy-bipyridine. Les nouveaux fluorophores possèdent une émission relativement intense avec une durée de vie de l,ordre de la nanoseconde, en solution et à l,état solide à 298,K ainsi que dans un verre à 77,K. Dans certain cas, la luminescence dépend de la longueur d,onde d,excitation, ce phénomène est attribué à (i) l,inefficacité du processus ESIPT, quand trop peu d,énergie vibrationnelle est introduite dans l,état Franck-Condon peuplé directement par la lumière d,excitation (ii) la présence d,un état excité supplémentaire qui désactive l,état fondamental sans passer par un processus ESIPT. Pour certains composés, l,effet de l,addition de sels de Zinc sur les spectres d,absorption et d,émission a été étudié : en particulier, des changements significatifs de fluorescence ont été observés, probablement due à la formation consécutive de complexes ligand/zinc de st,chiométrie 1:1 et 1:2, provenant de la coordination des cations ZnIIpar l,unité bipyridyl-diol, sauf quand une fonction terpyridine est présente. En fait, dans cette dernière espèce le zinc est préférentiellement coordiné par la terpyridine dans un ratio 1:1, et toute coordination supplémentaire de Zinc semble inhibée. Dans le composé hybride Bodipy/BP(OH)2,un transfert d,énergie quantitatif est observé du BP(OH)2vers le fluorophore Bodipy, entraînant une émission exclusive de la sous-unité Bodipy. Composti basati sulla subunità 6,6,-dimetil-3,3,-dididrossi-2,2,-bipiridina (BP(OH)2), variamente funzionalizzati, presentano fluorescenza relativamente intensa da stati eccitati formati attraverso trasferimento protonico nello stato eccitato (ESIPT). Bromo-funzionalizzazione dei composti di tipo BP(OH)2, seguita da reazioni catalizzate da Pd(0), permettono di connettere (con legame alchinico) gruppi funzionali quali il diazaboroindacene (Bodipy) o un modulo chelante (terpiridina) al frammento BP(OH)2. La struttura ai raggi X del composto contenente la terpiridina conferma la planarità dell,unità 3,3,-diidrossi-bipiridina. Le nuove specie presentano intensa emissione nella scala dei nanosecondi, in soluzione fluida ed allo stato solido a 298,K ed in matrice rigida a 77,K. In alcuni casi, la luminescenza dipende dalla lunghezza d,onda di eccitazione: questo fenomeno è attribuito a (i) inefficienza del processo ESIPT, quando non sufficiente energia vibrazionale è introdotta nello stato Franck-Condon a seguito di eccitazione luminosa o (ii) alla presenza di uno stato eccitato addizionale che si disattiva allo stato fondamentale senza passare dallo stato eccitato prodotto attraverso il meccanismo ESIPT. Per composti selezionati è stato anche studiato l,effetto della presenza di sali di zinco sulle proprietà di assorbimento elettronico e di luminescenza: significativi cambiamenti della fluorescenza sono stati osservati, come conseguenza della consecutiva formazione di addotti 1:1 e 1:2 (rapporto molare BP(OH)2/zinco), dovuta alla coordinazione di cationi di ZnIIda parte del bipiridil-diolo, che si verifica in tutti i casi studiati tranne in presenza di una subunità terpiridinica. In quest,ultimo caso, infatti, si forma soltanto l,addotto 1:1, e ulteriore coordinazione di cationi di ZnIIappare inibita. Nella specie ibrida Bodipy/BP(OH)2si verifica un completo trasferimento di energia elettronica dal BP(OH)2 al Bodipy, che porta ad emissione esclusivamente dalla subunità Bodipy, a piû bassa energia. [source] Photoinduced Excited State Intramolecular Proton Transfer of New Schiff Base Derivatives with Extended Conjugated Chromophores: A Comprehensive Theoretical SurveyCHINESE JOURNAL OF CHEMISTRY, Issue 6 2010Qi Wang Abstract This paper presented comprehensive theoretical investigation of excited state intramolecular proton transfer (ESIPT) of four new large Schiff base derivatives with extended conjugated chromophores. The properties of the ground state and the excited state of phototautomers of C1 to C4 [C1: 2-(4,-nitro-stilbene-4-ylimino)methylphenol; C2: 2-(4,-cyano-stilbene-4-ylimino)methylphenol; C3: 2-(4,-methoxyl-stilbene-4-ylimino)methylphenol; C4: 2-(4,- N,N -diethylamino-stilbene-4-ylimino)methylphenol], which included geometrical parameter, energy, rate constant, frontier orbit, Mulliken charge, dipole moment change, were studied by DFT (density functional theory), CIS (configuration interaction singles-excitation), TDDFT (time-dependent DFT) methods to analyze the effects of chromophore part on the occurrence of ESIPT and the role of substituent groups. The structural parameter calculation showed that the shorter RHN and larger ROH from enol to enol* form, and less twisted configuration in the excited state implied that these molecules could undergo ESIPT as excitation. Stable transition states and a low energy barrier were observed for C1 to C4. This suggested that chromophore part increased some difficulty to undergo ESIPT for these molecules, while the possibility of occurrence of ESIPT was quite high. The negative ,E* (,9.808 and ,9.163 kJ/mol) of C1 and C2 and positive ,E* (0.599 and 1.029 kJ/mol) of C3 and C4 indicated that withdrawing substituent groups were favorable for the occurrence of ESIPT. The reaction rate constants of proton transfer of these compounds were calculated in the S0 and S1 states respectively, and the high rate constants of these compounds were observed at S1 state. C1 even reached at 1.45×1015 s,1 in the excited state, which is much closed to 2.05×1015 s,1 of the parent moiety (salicylidene methylamine). Electron-donating and electron-withdrawing substituent groups had different effects on the electron density distribution of frontier orbits and Mulliken charges of the atoms, resulting in different dipole moment changes in enol*,keto* process. These differences in turn suggested that C1 and C2 had more ability to undergo ESIPT than C3 and C4. The ultraviolet/visible absorption spectra, normal fluorescence emission spectra and ESIPT fluorescence emission spectra of these compounds were predicted in theory. [source] Theoretical Studies on Proton Transfer Reactions of 8-Hydroxyquinoline Monomers and DimersCHINESE JOURNAL OF CHEMISTRY, Issue 6 2006Ji-Yang Zhao Abstract Density functional theory (DFT) of quantum chemistry method was employed to investigate proton transfer reactions of 8-hydroxyquinoline (8-HQ) monomers and dimers. By studying the potential energy curves of the isomerization, the most possible reaction pathway was found. The total energy of 8-hydroxyquinoline was lower than that of quinolin-8(1H)-one, whereas the order was reversed in dimers. The findings explained the contrary experimental phenomena. The minimum reaction barrier of intramolecular proton transfer was 47.3 kJ/mol while that in dimer was only 25.7 kJ/mol. Hence it is obvious that proton transfer reactions of 8-HQ monomer have a considerable rate but it is easier to proceed for 8-HQ dimer than monomers. It implied that the hydrogen bond played an important role in depressing the activation energy of reaction. The mechanism of the tautomerization was discussed on the basis of theoretical results. [source] | |||||||||||||