Emission Spectra Of Molecules Research Articles

Label-Free Ratiometric Imaging of Serotonin in Live Cells.

Ratiometric imaging can quantitatively measure changes in cellular analyte concentrations using specially designed fluorescent labels. We describe a label-free ratiometric imaging technique for direct detection of changes in intravesicular serotonin concentration in live cells. At higher concentrations, serotonin forms transient oligomers whose ultraviolet emission is shifted to longer wavelengths. We access the ultraviolet/blue emission using relatively benign three-photon excitation and split it into two imaging channels, whose ratio reports the concentration. The technique is sensitive at a physiologically relevant concentration range (10-150 mM serotonin). As a proof of principle, we measure the increase of intravesicular serotonin concentration with the addition of external serotonin. In general, since emission spectra of molecules are often sensitive to concentration, our method may be applicable to other natively fluorescent intracellular molecules which are present at high concentrations.

Absorption and fluorescence emission spectra of molecules containing azo and/or oxadiazole units

The ground state structures of a series of organic molecules containing azo and/or oxadiazole units were obtained by means of density functional theory B3LYP/6-31G(d) method. The first singlet excited state structures were optimized by virtue of singlet-excitation configuration interaction CIS/6-31G(d) method. The absorption and fluorescence emission spectra were then evaluated via the time-dependent density functional theory B3LYP and PBE1PBE methods with 6-311++G(3df,2p) basis set. The calculation results show that compared with those of their parent molecules A-H, B-H, C-H, D-H, the absorption and emission wavelength values of all the derivatives show red shifts. The derivatives containing both the oxadiazole and methoxyl units are good candidates for longer absorption wavelength materials. The effects of azo, oxadiazole, and methoxyl units on the absorption and emission wavelength were discussed.

Absorption and Emission Spectra of Solvated Molecules with the EOM-CCSD-PCM Method.

The accurate calculation of transition energies and properties of isolated molecules is not enough for realistic simulations of their absorption and emission spectra in solution. In fact, the solvent influences the solute geometry, electronic structure, and response to external fields, and a proper description of the solvent effect is fundamental. However, the computational cost of including explicit solvent molecules around the solute becomes rather onerous when an accurate method such as the equation of motion coupled cluster singles and doubles (EOM-CCSD) is employed. The polarizable continuum model of solvation (PCM) may provide an efficient alternative to explicit models, since the sampling of solvent configurations is implicit and the solute-solvent mutual polarization is naturally accounted for. In this contribution, the absorption and emission spectra of molecules in solution are modeled through the EOM-CCSD-PCM method. The equilibrium solvation regime is employed for the geometry optimization of the solute molecule in the ground and excited states, while the nonequilibrium solvation regime is employed for vertical transitions. The theory, implementation, and prototypical applications of the method are presented. The numerical tests involve solvents that are particularly challenging for PCM: low-polar and protic polar solvents. Nonetheless, the experimental trends are well reproduced, and the overall agreement with the measured data is remarkable.

Calibration and Uncertainty Analysis of an Optical Emission Spectrometer Measuring the Absolute Spectral Radiant Exitance of UV Signatures

AbstractAn optical emission spectrometer (OES) was designed and constructed to detect the absolute spectral radiant exitance of UV signatures for a wavelength range of 240 nm to 440 nm. Using a directly heated graphite black body furnace operating at a temperature of 3000 K, the spectral response of the OES in the UV range was calibrated. To evaluate the performance of the OES system, the emission spectra of molecules were measured in a butane flame and the absolute emissions of the UV signatures were calculated. The uncertainty of the absolute measurement of the UV signature was analyzed by considering various uncertainty budgets, and the total uncertainty of the OES was found to be 1.66 %.

Luminescence Study of cis - and trans -Stilbenes in the Sol-Gel System

The emission spectra of cis- and trans- stilbene molecules doped in sol-gels(tetraethoxysilane system) have been measured during the sol-gel transformation. Changes in the emission spectra of both molecules were observed as the system changed from sol stage to dried glass over a period of 14 days. Our results indicate that the motion of the cis→trans photoisomerization decreases in accord with the rigidity changes of the surrounding system. Although the trans→cis photoisomerization was not observed in the sol-gel system, the twisting motion of the single bond between the phenyl group and the ethylene moiety during the photoexcitation was detected in this system. The existence of the transient intermediates will be discussed to interpret the subtle changes of the emission spectra of the stilbene molecules encapsulated in the sol-gel system.

Polymer chain effects on ground state and excited state charge transfer processes

It is shown that polymer chains containing electron donor units may, because of favourable configurational and conformational effects, provide extra stabilisation for the positively charged (cation radical) components of excited states of charge transfer complexes and of exciplexes. Exciplex formation between carbazole and terephthalate units is evidenced by the appearance of new emission bands which are mainly intra-macromolecular in origin for polymer solutions but which may be mainly intermacromolecular in origin for polymer films. The latter phenomenon affords a possible new technique for the study of polymer miscibility in films. Twisted internal charge transfer states such as are detected via the fluorescence emission spectra of molecules like ethyl 4-dimethylaminobenzoate may be used to study polymer-solvent interactions in the liquid phase and high frequency rotational relaxation in polymer films.

Interpretation of Polarized Absorption and Emission Spectra of Molecules Incorporated in Stretched Polymer Films

Abstract Different methods for the interpretation of linear dichroic spectra of molecules incorporated in uniaxial matrices are discussed. A method based on the combination of both polarized absorption and emission measurements is described for the resolution of absorption and emission spectra into their different polarized components, and for the investigation of molecular distributions in the oriented matrix. The distributions of some planar molecules of different shapes incorporated in stretched polyethylene films are presented.

On the relation between absorption and emission spectra of molecules in solution

The universal relation between absorption and fluorescence spectra derived by Stepanov in 1957 is reexamined to assess the relative merits of two of the inferences usually drawn from its use in the analysis of data: elevated excited state temperatures (“warm fluorescence”) and inhomogeneous broadening of the molecular spectra. Of these, only the latter appears to give a satisfactory explanation of the anomalous temperatures derived using the Stepanov method in condensed media, and in particular, a purely “warm fluorescence” interpretation implies that a distinct curvature should appear in plots which experimentally appear to be straight lines.

Laser pyrolysis: Effect of ambient gases on molecular spectral emission

Observations are reported on the emission spectra of molecules in luminous plumes produced by focussing a Q-switched ruby laser beam on various solids (mostly elements) in the following gases at various pressures; air, H 2, N 2, SF 6 and O 2.