1,721,052 research outputs found
AN UV-VISIBLE SPECTROSCOPIC DATABASE OF ORGANIC DYES: A PROMISING AND HELPFUL TOOL FOR A SCIENTIFIC KNOWLEDGE OF WORKS OF ART
No full textFluorescence Spectroscopy: a powerful technique for the non-invasive characterization of artworks
No full textAfter electronic excitation by ultraviolet or visible radiation, atoms and molecules can undergo thermal or radiative deactivation processes before relaxing to the ground state. They can emit photons with longer wavelengths than the incoming exciting radiation, that is, they can fluoresce in the UV-vis-near-infrared (NIR) range. The study of fluorescence relaxation processes is one of the experimental bases on which modern theories of atomic and molecular structure are founded. Over the past few decades, technological improvements in both optics and electronics have greatly expanded fluorimetric applications, particularly in analytical fields, because of the high sensitivity and specificity afforded by the methods. Using fluorimetry in the study and conservation of cultural heritage is a recent innovation. In this Account, we briefly summarize the use of fluorescence based techniques in examining the constituent materials of a work of art in a noninvasive manner. Many chemical components in artwork, especially those of an organic nature, are fluorescent materials, which can be reliably used for both diagnostic and conservative purposes. We begin by examining fluorimetry in the laboratory setting, considering the organic dyes and inorganic pigments that are commonly studied. For a number of reasons, works of art often cannot be moved into laboratories, so we continue with a discussion of portable instruments and a variety of successful “field applications” of fluorimetry to works of cultural heritage. These examples include studies of mural paintings, canvas paintings, tapestries, and parchments. We conclude by examining recent advances in treating the data that are generated in fluorescence studies. These new perspectives are focused on the spectral shape and lifetime of the emitted radiation. Recent developments have provided the opportunity to use various spectroscopic techniques on an increasing number of objects, as well as the ability to fully characterize very small amounts of sample, either in a laboratory setting or on site. Thus, a new technological highway is open to scientists; it is still difficult to navigate but offers an enormous potential for investigating objects without touching them. Fluorescence spectroscopy is one of the most important of these techniques
Carthamus tinctorius L.: A photophysical study of the main coloured species for artwork diagnostic purposes
No full textIn this work a spectrophotometric and fluorimetric study of yellow and red extracts from Carthamus tinctorius L. in solution and on dyed textiles is reported. The red dye, precipitated as an insoluble organic pigment, was also characterized as powder substrate and on painting mock-ups using different pictorial techniques based on the use of diverse binders. The dyestuffs were directly extracted from dried petals of Carthamus flowers following ancient recipes adapted for laboratory use. The main quinochalcone dyes (hydroxysafflor yellow A, safflor yellow A, anhydrosafflor yellow B and carthamin) were separated and isolated through both analytical and preparative High Performance Liquid Chromatography-Photo Diode Array and subsequently identified through Liquid Chromatography-Mass Spectrometry Quadrupole Time-Of-Flight analysis. The compounds were then studied in solution so as to supply information concerning the scarcely studied fluorescence of these materials. Based on the photophysical behaviour determined in solution, spectral properties of dyed textiles and pictorial mock-ups were discussed. The results obtained on red reference samples are of peculiar relevance for the non-invasive identification of carthamin whose specific absorption and emission features have been clearly detected on a 16th century tapestry fragment
Photophysics of cyanophenylpyrroles: Investigation of solvatochromic properties and charge transfer by ultrafast spectroscopy and DFT calculations
No full textA comprehensive investigation of the photophysics of cyanophenylpyrrole derivatives has been carried out by means of steady-state, nanosecond and femtosecond resolved absorption and fluorescence techniques, and quantum-mechanical calculations. This study revealed that the investigated compounds (1-3) are highly fluorescent molecules (Phi(F) = 0.2-0.9) with lifetimes in the range 2-8 ns. The compounds exhibit weak hypsochromic solvatochromic changes in the absorption and large batochromic shifts in the fluorescence spectra. An increase in solvent polarity does not induce a reduction of the fluorescence quantum yields, but causes a lengthening of the fluorescence lifetimes. The density functional theoretical calculations predicted similar energies for S-1 and S-2, probably resulting in the state mixing and IT character of the relaxed S-1 state. Furthermore, the computed dipole moments have been found to be higher in the excited with respect to the ground state, in agreement with the strong solvatochromic properties experimentally observed in the emission spectra. Ultrafast transient absorption measurements indicated the existence of three decay components assigned to the hot Franck-Condon S-1 state that undergoes vibrational cooling (VC, several picoseconds), the species formed by VC undergoing a torsional motion of the C-C bond between the phenyl and the pyrrole ring (several hundreds of picoseconds), and the relaxed S-1 state that decays radiatively (nanoseconds). Indeed, the calculated optimized geometry of 1-3 in the ground state is characterized by a dihedral angle between the pyrrole and phenyl moieties of about 10-25 degrees, whereas the S1 state is predicted to be more planar than S-0. Due to the fast population of the relaxed S-1 states, the typical dual fluorescence reported for N-phenylpyrroles was not observed for 1-3. (C) 2014 Elsevier B.V. All rights reserved
Historically Inspired Strategy to Achieve Sustainable and Effective Coloration of Bioplastics
No full textThe use of historical organic pigmentsis an interesting strategyto provide color nuances to biopolymers while achieving good solidoptical effects. In this work, aqueous extracts of logwood (LW) aretested as a natural source of color for the sustainable productionof an organic purple pigment (LWP) taking advantage of the historicallake approach. Different amounts of LWP (0.01-2% wt) are usedfor the effective coloration of polycaprolactone (PCL), polybutylenesuccinate (PBS), and polylactide (PLA). The full characterizationof LWP and LWP-treated biopolymer samples enables the spectral andcolor properties of the composites to be defined where the exceptionalcolor efficiency of LWP is demonstrated by the very low amount (0.5%wt) necessary to reach the saturation. The evolution of spectra andcolor coordinates under accelerated aging conditions is monitoredfor LWP-polymer samples. A 10-12% decrease of the visible absorptionband is detected after prolonged irradiation, resulting in a moderatecolor fading for PBS compared to PCL samples, while negligible changesare observed for PLA samples. The results demonstrate that LWP constitutesan efficient and sustainable source of color for the analyzed polymerswithout causing significant changes in the tensile and thermal propertiesof the polymeric matrix.Apurple pigment is prepared from a natural source followinga historical and sustainable procedure for the effective colorationof three different biopolymers
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