Absorption photophysics

Becker RS, Seixas de Melo J, Maganita AL, Elisei E (1996) Comprehensive evaluation of the absorption, photophysical, energy transfer, structural, and theoretical properties of -oligothiophenes with one to seven rings. J Phys Chem 100 18683-18695... 

A number of electronic and photochemical processes occur following band gap excitation of a semiconductor. Figure 5 illustrates a sequence of photochemical and photophysical events and the possible redox reactions which might occur at the surface of the SC particle in contact with a solution. Absorption of light energy greater than or equal to the band gap of the semiconductor results in a shift of electrons from the valence band (VB) to... 

The reduced symmetry of the chromophore, which still contains 187t-electrons and is therefore an aromatic system, influences the electronic spectrum which shows a bathochromic shift and a higher molar extinction coefficient of the long-wavelength absorption bands compared to the porphyrin, so that the photophysical properties of the chlorins resulting from this structural alteration render them naturally suitable as pigments for photosynthesis and also make them of interest in medical applications, e.g. photodynamic tumor therapy (PDT).2... 

Ultraviolet absorption spectra were also applied in the investigations on photophysical, photochemical, and photochromic behavior of some... 

More recently, we have succeeded in the preparation of the next generation compound 15 (Fig. 7) for which the molar absorptivity is approximately 450,000 M cm b The photophysical properties of 15 have not been yet investi-... 

Methanofullerene 20 with phenylacetylene dendrimer addends has also been reported [45] (Fig. 10). The UV absorption of fullerodendrimer 20 is particularly strong and is mainly attributed to transitions located on the two dendritic branches of the molecule. The photophysical investigations revealed that the large poly(aryl)acetylene branches act as photon antennae [46]. 

To substitute the strongly bound axial CO ligand of the ruthenium or osmium center, it is necessary to employ more drastic conditions than simple stirring at room temperature. Imamura (11,20) used photolysis to synthesize porphyrin trimers on the basis of simultaneous coordination of two 4-pyridyl porphyrins to the same ruthenium porphyrin (12, Fig. 3). Some interesting photophysical behavior was observed for these systems. The trimers have an extra UV-Vis absorption band at about 450 nm which is ascribed to metal-ligand charge transfer (MLCT), a d7r(Ru(II))-7r (OEP) transition. This band shows a batho-chromic shift in more polar solvents, and decreased in intensity when... 

The various intramolecular processes initiated by light absorption are illustrated schematically in Figure 1.1. Such a schematic representation of the energy levels and photophysical processes which can occur in the excited... 

We (fl) have reported the photophysical processes of a series of model esters of PET, and tentatively assigned the fluorescence and phosphorescence of the aromatic esters as (n, tt ) transitions, respectively. We (9) also performed an extensive study of the photophysical processes available to dimethyl terephthalate (DMT) in order to relate this monomeric species to the PET polymer. In 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) (Table I), DMT has three major,absorptions which are according to Platt, s notation 191 nm, A- B, e = 40,620 1 mole" cm"1 244 nm, A-dLaT e = 23,880 1 mole-) cm" 289 nm, A U, e = 1780 1 mole")cm. ... 

Photophysical Processes in Dimethyl 4,4 -Biphenyldicarboxy-late (4,4I-BPDC). The ultraviolet absorption spectrum of dimethyl 4,4 -biphenyldicarboxyl ate was examined in both HFIP and 95% ethanol. In each case two distinct absorption maxima were recorded, an intense absorption near 200 nm and a slightly less intense absorption near 280 nm. The corrected fluorescence excitation and emission spectra of 4,4 -BPDC in HFIP at 298°K shows a single broad excitation band centered at 280 nm with a corresponding broad structureless emission band centered at 340 nm. At 77°K, the uncorrected phosphorescence spectra shows a single broad structureless excitation band centered at 298 nm, and a structured emission band having maxima at 472 and 505 nm with a lifetime, t, equal to 1.2 seconds. 

Photophysical Processes in Pol,y(ethy1eneterephthalate-co-4,4 -biphenyldicarboxyl ate) (PET-co-4,4 -BPDC). The absorption and luminescence properties of PET are summarized above. At room temperature the absorption spectrum of PET-co-4,4 -BPDC copolymers, with concentrations of 4,4 -BPDC ranging from 0.5 -5.0 mole percent, showed UV absorption spectra similar to that of PET in HFIP. The corrected fluorescence spectra of the copolymers in HFIP exhibited excitation maxima at 255 and 290 nm. The emission spectrum displayed emission from the terephthalate portion of the polymer, when excited by 255 nm radiation, and emission from the 4,4 -biphenyldicarboxylate portion of the polymer when excited with 290 nm radiation. 

Photophysical Processes in Pi butyl 4,4 -Sulfonyldibenzoate (4,4 -SD). The UV absorption spectra of dibutyl 4,4 -sulfonyl-dibenzoate (4,4 -SD) in both HFIP and 95% ethanol showed similar absorptions. The corrected excitation and emission fluorescence spectra of 4,4 -SD in HFIP at 298°K showed a structured excitation with band maxima at 236, 286, and 294 nm and a structured emission exhibiting band maxima at 322, 372, and 388 nm. The uncorrected excitation and phosphorescence spectra of 4,4 -SD in a 95% ethanol glass at 77°K displayed excitation band maxima at 268, 282, and 292 nm with strong phosphorescence emission with band maxima at 382, 398, and 408 nm with a mean lifetime (t) of 1.2 sec. 

Photophysical Processes in PET-4,4 -SD Copolymers. PET-4,4 -SD copolymers have UV absorption spectra similar to that of PET homopolymer in HFIP solution. Band maxima were exhibited at about 290, 245, and 191 nm in all the polymers. 

Fluorophores containing 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene as a core skeleton are commonly designated as BODIPY fluorophores. Due to their useful photophysical properties including high fluorescence quantum yields, high molar absorption coefficient, narrow absorption and emission band width, and their high photostability [50], BODIPY dyes are proven to be extremely versatile and useful in many biological applications Fig. 11 [68]. 

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