Abstract Steady‐state absorption, fluorescence excitation, and emission spectra of 6‐methoxy quinoline (6‐MQ) were measured at room temperature in cyclohexane, dioxane, ethanol, acetonitrile, water, and water–dioxane solvents. Absorption spectra of cyclohexane, n‐hexane, and isopentane solutions show resolved vibronic structure at room temperature. However, the excitation spectrum of cyclohexane solution is structureless and is found to be emission wavelength dependent, indicating the formation of at least two distinct species in the ground state. Similar behavior was observed in dioxane and water–dioxane solutions. For all other solutions, the fluorescence excitation spectrum of 6‐MQ was found to be the same for different emissions. Emission of 6‐MQ in all solvents consisted of two bands with their maxima around 355 nm (I) and 430 nm (II), the actual positions and the relative intensities being dependent on the solvent used. The bands I and II were respectively attributed to normal and protonated/H‐bonded species of either 1La or 1Lb states or mixed (1La/1Lb) state of ππ* character. Fluorescence decay of this dye in all solvents monitored over each emission maximum showed biexponential behavior, and the analysis yielded two different lifetime components for each emission band. The short and long fluorescence decay components were respectively in the range of 0.30–3.00 ns and 18–20 ns. The observed emission characteristics coupled with the nature of the fluorescence polarization spectra and two different decay components for each emission suggest the existence of two different conformers having two different excited electronic states. 相似文献
The photophysicochemical properties of selected fluoroquinolones in different solvents of various physical properties, including polarity and hydrogen bonding ability, were investigated using steady state fluorescence spectroscopy. The solvent-dependant fluorescence emission spectra of selected fluoroquinolones, namely ciprofloxacin (CIPR) and enrofloxacin (ENRO), were employed to gain insights concerning its photophysicochemical properties of interests. Interestingly, fluorescence spectra of the selected drugs exhibited structured emission spectra in nonpolar solvents such as hexane, whereas unstructured spectra were observed in more polar solvents such as alcohols and water. Also, a notable bathochromic shift in $ \lambda_{{\max }}^{{em}} $ was observed in fluorescence spectra of both drugs with increasing solvent polarity that resulted in biphasic behavior upon applying the Lippert-Mataga correlation that correspond to general and specific solvent effects. Applying the Lippert-Mataga correlation to the fluorescence spectra of CIPR and ENRO in various solvents was employed to estimate the dipole moment difference between the ground and excited states of them, $ \Delta \mu \left( {{\mu_e} - {\mu_g}} \right) $, where obtained results revealed the values of 9.4 and 16.2 Debye for the LE and ICT states of ENRO, respectively, and 8.0 and 16.2 Debye for the LE and ICT states of CIPR, respectively. Multiple linear regression analysis (MLRA) based on Kamlet-Taft equating was applied against absorption frequency (νabs), emission frequency (νem), Stokes shift (?ν), and fluorescence quantum yield (Φf), where obtained results revealed excellent correlation (R: 0.916–0.966) that are consistent with other results considering the effect of solvent polarizability, hydrogen bonding ability, and viscosity on the photophysicochemical properties of the studied fluoroquinolones. 相似文献
The spectral properties such as singlet absorption, molar absorptivity, emission spectra, fluorescence quantum yield and excited state lifetime of 3-(4′-dimethylaminophenyl)-1-(2-furanyl)prop-2-en-1-one (DMAFP) have been determined in different solvents. DMAFP dye exhibits a large red shift in both electronic absorption and emission spectra as the solvent polarity increases, indicating a large change in the dipole moment of molecules upon excitation. A crystalline solid of DMAFP gives an excimer like emission at 566 nm due to the excitation of molecular aggregates. This is expected from the idealized crystal structure of the dye that belongs to the B-type class of Steven's classification. The ground and excited state protonation constants of DMAFP are calculated and amounted to 1.71 and 8.3, respectively. DMAFP acts as a good laser dye upon pumping with nitrogen laser (λex=337.1 nm) in chloroform, methylene chloride and dioxane and gives laser emission in the range 460–590 nm. The laser parameters such as the tuning range, gain coefficient (α), emission cross section (σe) and half-life energy (E1/2) are calculated. The photoreactivity and net photochemical quantum yield of DMAFP in chloromethane solvents are also studied. 相似文献
The absorption and steady-state fluorescence spectra of fluorenone, 1-hydroxyfluorenone, and 3-dimethylaminofluorenone have been obtained for various concentrations in a series of non-polar and polar solvents. The substituents (-OH and -N(CH3)2) as the electron-donating functional groups cause a large shift of the longwave absorption band and Stokes' shift of the monomer- and excimer-fluorescence bands in comparison with fluorenone. The total emission spectrum of 3-dimethylaminoflourenone in polar aprotic solvents exhibits a new band at 500 nm originating form the emission of the twisted intramolecular charge transfer (TICT) isomer. The excited state dipole moments of the emiting species of the molecule studied are determined using the solvatation shift method and calculated values of the ground state dipole moments. 相似文献
The fluorescence properties of bisheterocyclic compounds that contain purine and the 3-hydroxyquinolin-4(1H)-one skeleton connected with an aliphatic spacer of a different length/structure (3HQP) were examined. It was found that
the introducing of the spacer-purine scaffold led in the comparison to 3HQs themselves to (1) the possibility of the effectual
excitation in the wider range of excitation wavelengths, moreover, some derivatives can be excited at relatively high wavelengths
around 400 nm, (2) the lowering of the quantum yield and (3) the slight longer wavelength shift of the dual emission spectra.
Tested organic solvents did not affect significantly the 3HQP fluorescence properties. The characters of emission spectra
as well as the quantum yields of 3HQPs were notably influenced by the ratio of water and DMSO in their composed mixture applied
as a solvent. With increasing water content in the mixture both I1/I2 and the quantum yield decreased. 相似文献
Electronic absorption and fluorescence emission spectra of DMDMAQ (1,4-dimethoxy-2,3-dimethyl-9,10-anthraquinone) have been
studied as a function of solvent composition in some binary mixtures and in different neat solvents. The binary mixtures consist
CCl4 (Carbon tetrachloride)-DMSO (Dimethylsulfoxide), EtOH (Ethanol)-DMSO, and CCl4-EtOH combination of single solvents. The wavelength maxima of the absorption band for DMDMAQ are quite solvent sensitive
in aprotic solvents. But, in protic solvent, there is no marked shift in absorption and emission maximum which shows the absence
of specific interaction. Excited state shows increasing shift with increasing solvent polarity compared to ground state. The
ratio of dipole moment in the excited state to that in the ground state was calculated. Different criteria were considered
to analyse preferential solvation characteristics in different binary mixtures, viz., local mole fraction (), solvation index (δS2) and exchange constant (K12). 相似文献
The absorption and fluorescence characteristics of 3-(4′-dimethylaminophenyl)-1-(2-thienyl)prop-2-en-1-one (DMATP) have been investigated in different solvents. DMATP dye exhibits a large red shift in both absorption and emission spectra as solvent polarity increases, indicating a large change in the dipole moment of molecules upon excitation due to an intramolecular charge transfer interaction. The fluorescence quantum yield depends strongly on the properties of the solvents, which was attributed to positive and negative solvatokinetic effects. A crystalline solid of DMATP gave an excimer like emission at 570 nm due to the excitation of molecular aggregates. This is expected from the idealized crystal structure of the dye that belongs to the B-type class of Steven's classification. A dye solution ca. 10−3 mol dm−3 in CHCl3 gave a good laser emission in the range 480–560 nm with emission maximum at 530 nm upon pumping by nitrogen laser (λex=337.1 nm). The excitation energy transfer from 7-dimethylamino-4-methyl coumarine (DMC) to DMATP has been also studied in CHCl3 and the values of energy transfer rate constant and critical transfer distance indicate a Főrster-type mechanism. The photoreactivity and net photochemical quantum yield of DMATP in chloromethane solvents are also determined. We applied semiempirical MO calculation using AMI and ZINO/S calculation to understand the geometric and electronic structure of DMATP molecule in both ground and excited states. 相似文献
We examined the steady-state and time-resolved emission of liver alcohol dehydrogenase resulting from one-photon and two-photon excitation. Previous studies with one-photon excitation revealed that the two nonidentical tryptophan residues display different emission spectra and decay times. The use of two-photon excitation resulted in similar emission spectra, multiexponential intensity decays, time-resolved emission spectra, and anisotropy decays as was observed for one-photon excitation. These results suggest that both nonidentical tryptophan residues are excited to a similar extent for one- and two-photon excitation. However, the limiting anisotropy (r0) with two-photon excitation from 585 to 610 nm is below 0.1 and appears distinct from that observed previously forN-acetyl-l-tryptophanamide.Abbreviations LADH
liver alcohol dehydrogenase
- -NAD+
-nicotinamide adenine dinucleotide
- OPE
one-photon excitation
- OPIF
one-photon induced fluorescence
- TPE
two-photon excitation
- TCSPC
time-correlated single photon counting
- TPIF
two-photon induced fluorescence 相似文献
The photophysical properties such as singlet absorption, molar absorptivity, fluorescence spectra, fluorescence quantum yield (?f) and transition dipole moment (μ12) of 3-(4-dimethylamino-phenyl)-1-{6-[3-(4-dimethylamino-phenyl)-acryloyl]-pyridin-2-yl}-propanone (DMAPAPP) have been studied in different media. DMAPAPP exhibits a large red-shift in both absorption and emission spectra as the solvent polarity increases, indicating a large change in dipole moment of molecule upon excitation. The fluorescence quantum yield depends on the nature of the solvent. The absorption and emission spectra of DMAPAPP in dioxane–water mixture are also studied. The effect of different type of surfactants to determine their critical micellar concentration (CMC) and the microemulsion effect on the electronic absorption and emission spectra of DMAPAPP are recorded. The effect of acidity on the electronic absorption and emission spectra of DMAPAPP is studied to determine the pKa and pKa? values. 相似文献
Spectral characteristics of 2-(4′-amino-3-pyridyl)benzimidazole (4-A3PyBI) have been studied in different solvents, as well as at different acid or base concentrations using absorption, fluorescence excitation and fluorescence spectroscopy. Excited singlet state (S1) lifetimes for each species were measured using nanosecond time-dependent spectrofluorimeter. AM1 semi-empirical and density functional theoretical (DFT) calculations were performed on each species for the spectral assignment. From the above results it is concluded that 4-A3PyBI exists only in the amine form. First protonation occurs at pyridineN- atom and second protonation at the benzimidazole (BI)N- atom. When dication (DC) species is excited, two emission bands are observed, having the same fluorescence excitation spectra, suggesting the same ground state (S0) precursor. Short wavelength (SW) emission band is assigned to the π-π* transition and long wavelength (LW) emission to the charge transfer transition. First deprotonation in S0 state occurs from >N-H moiety, whereas in S1 state it is from -NH2 group. Monoanion (MA) so formed in S1 state is non-fluorescent. Dianion (DA) is formed by further deprotonating >N-H moiety in S1 state and it is fluorescent. pKa values were determined and discussed. 相似文献
E,E-2,5-bis[2-(3-pyridyl)ethenyl]pyrazine (BPEP) has been prepared by aldol condensation between 2,5-dimethylpyrazine and pyridine-3-carboxaldehyde. It is characterized by IR, 1H NMR, and 13C NMR. The electronic absorption and emission properties of BPEP were studied in different solvents. BPEP displays a slight solvatochromic effect of the absorption and emission spectrum, indicating a small change in dipole moment of BPEP upon excitation. The dye solutions (1 × 10?4 M) in CHCl3, EtOH and dioxane give laser emission in blue region upon excitation by a 337.1 nm nitrogen pulse (λ = 337 nm). The tuning range, gain coefficient (α) and emission cross – section (σe) have been determined. Ground and excited states electronic geometric optimizations were performed using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), respectively. A DFT natural bond analysis complemented the ICT. The simulated maximum absorption and emission wavelengths are in line the observed ones in trend, and are proportionally red-shifted with the increase of the solvent polarity. The stability, hardness and electrophilicity of BPEP in different solvents were correlated with the polarity of the elected solvents. BPEP dye displays fluorescence quenching by colloidal silver nanoparticles (AgNPs). The fluorescence data reveal that radiative and non-radiative energy transfer play a major role in the fluorescence quenching mechanism. 相似文献
The fluorescence and phosphorescence properties of 2-isopropoxy phenyl-N-methyl carbamate, [formula (I)], have been studied in polar and non-polar solvents, at room temperature and at 77 K. The fluorescence quantum yield of (I) in cyclohexane at room temperature, and the ratio of phosphorescence to fluorescence yield in three solvents at 77 K have been determined. Polarization studies have been carried out on both the fluorescence and phosphorescence emission. Phosphorescent lifetimes, τp, have been measured in various solvents and were found to be non-single exponential in all cases. The data provides an understanding of the excitation and emission processes in (I) and should be of use in the developement of spectral techniques for the detection of this molecule. 相似文献
Under strongcw-excitation ruby crystals exhibit complex anti-Stokes fluorescence spectra in the near ultraviolet. Based on ring dye laser excitation spectra, fluorescence decay and concentration dependence, we show that these spectra can be decomposed into single ion emissions and a cooperative emission at the double energy of the2E4A2 transition. The unusual vibronic sideband of the latter suggests a general mechanism for the coupling of distant ions in polar insulators involving the electric field of longitudinal optical phonons.Work supported by Sonderforschungsbereich 65 Frankfurt/Darmstadt 相似文献
The fluorescence characteristics of the Schiff bases 2-(3-pyridylmethyliminornethyl)phenol (1), 2-(2 pyridyliminomethyl)phenol (2), N.N-bis(salicylidene)-2,3-pyridinediamine (3), N,N'-bis(salicylidene)-2,6-pyridinediamine (4) and 2-(2-amino-4-methoxymethyl-6-methyl-3-pyridylmethyliminomethyl)phenol (5) were studied in various solvents at different pH values. Corresponding quantum efficiencies were determined. Compound 1, which showed a tendency towards tautomeric mterconversion to ketoamine in polar protic solvents, was not fluorescent at pH < 8. The fluorescence of other compounds was very sensitive to solvent polarity and the pH of the medium. Compounds 2-4, preferably present as enolimines in all solvents, were not fluorescent in non-polar and moderately polar solvents, whereas weak emission was observed in polar solvents, like methanol, dimethylformamide and dioxane/water 1/1 (0.001 < Q < 0.072). A significant increase in Stokes shifts and in quantum efficiencies was noted as a result of increasing polarity of dioxane/water mixtures, indicating specific interactions with polar water molecules. The emission was promoted at acidic pH values where a pyridinium cation was formed (0.061 < Q < 0.519, in dioxane/water 1/1 at pH 3.4). Compound 5, which was a tautomeric mixture of enoiimine and cyclic diamine in all solvents, was fluorescent in polar as well as in non-polar media. The quantum efficiency varied dependent on the solvent and pH (0.023 <Q< 0.435). The cyclic diamine, i. e. the more rigid structure was supposed to be responsible for the fluorescence in non-polar and aprotic solvents as well as at neutral, and weakly basic pH values. 相似文献
The interaction between retinyl palmitate molecules and their environment in binary water/p-dioxane and water/isopropyl alcohol solvents was studied under different solvent polarities. The binary solvent polarities were changed by changing the molar ratios of water to p-dioxane (or isopropyl alcohol). The fluorescence emission and fluorescence excitation spectra were analyzed. In binary solvents, the interaction between retinyl palmitate molecules and environments of different polarities leads to the self-organization of retinyl palmitate, and as a result, different fluorescence centers are created. The similar fluorescence properties of these centers in different binary solvents were interpreted as a water driving force inducing the self-organization of retinyl palmitate. The possible consequences of this phenomenon for misleading interpretation of model studies of retinol interaction with retinol transporting proteins are also discussed. 相似文献
Polynuclear aromatic hydrocarbons (PAHs) are a vast class of organic compounds. Many PAHs show carcinogenic effects, which in general are strongly dependent on their molecular structure. Hence, some, even structurally strongly related, PAHs may show a large difference in carcinogenicity. Low-temperature fluorescence spectroscopy of PAHs embedded in a polycrystalline n-alkane matrix (or Shpol'skii matrix) is a powerful technique to identify trace amounts of PAHs in complex samples. The fluorescence spectra show vibrational resolution, so that even very similar isomers can be discerned. Since the Shpol'skii effect is matrix-induced, both the fluorescence emission and excitation spectra display narrow lines, so that a maximum of information can be obtained via the application of fluorescence excitation–emission matrices. To demonstrate the possibilities of high-resolution excitation–emission matrices (HREEMs), a marine sediment sample has been investigated, containing, among others, benzo[a]pyrene and benzo[k]fluoranthene, PAHs with very similar spectral features, but the former being a notorious carcinogenic compound. The two PAHs could be clearly distinguished in the HREEM. Subsequently, a comprehensive set of data was obtained with a multitude of combinations of excitation and emission wavelengths, which allows for the screening of many PAHs, including all priority pollutants, in one analysis step. A simpler and also highly informative screening method, which can be applied over a wide wavelength region, is that of synchronous scanning: the fluorescence signal is obtained by scanning the excitation and emission monochromators simultaneously. When a fixed wavenumber difference is maintained during the scan, the screening can be done based on structural characteristics of the molecules of interest. High-resolution constant-energy fluorescence (CESF) spectroscopy also has been applied to acquire vibrationally resolved spectra for PAHs in the marine sediment sample. When a relatively small energy difference (<800 cm–1) is applied between excitation and emission wavelength, simple CESF spectra are obtained, which allow for rapid and specific screening of PAHs. Larger energy differences lead to more complex spectra, with spectral features showing up due to various combinations of vibronic excitation and vibronic emission of the same molecule. 相似文献
It is found that the excitation spectra of the dual fluorescence of 3-hydroxyflavone are different for different recording wavelengths and that the intensity ratio of the emission of the normal and tautomeric (with intramolecular proton transfer) forms upon selective UV excitation in the regions of the S1, S2, and S3 singlet absorption bands strongly depends on the excitation wavelength. The results obtained directly point to the existence of an additional channel of population of the excited state of the tautomeric form and are explained by the intramolecular proton transfer through the S2 and S3 excited singlet states of fluorophore molecules. The constants of this transfer are estimated using analytical relations for the steady-state fluorescence excitation. 相似文献
The steady-state excitation anisotropy spectra of fluorene derivatives were measured in viscous solvents, under the one- and two-photon excitation, over a broad spectral range (UV–Visible). The orientation of their absorption transition moments for the first, S0S1, and second, S0S2, excited states were determined. It was shown experimentally that a decrease in the angle between S0S1and S0S2 transitions corresponded to an increased value of two-photon absorption (2PA) cross section for these molecules. Two-photon excitation anisotropy was nearly constant over the spectral region investigated (in contrast to one-photon excitation anisotropy spectra) and can be roughly explained by a simple model of 2PA based on the single intermediate state approximation. For comparison, the same trend in two-photon excitation anisotropy was observed for Rhodamine B inglycerol. 相似文献