Fluorescence photophysics

More recently, several groups have investigated electrostatic effects on the fluorescence quenching of hydrophobic chromophores covalently attached to various polyanions. The photophysics of the chromophores incorporated in the polyeletrolytes at small mole fractions is relatively simple, because no interaction is expected to occur between the incorporated chromophores. For this reason, most of the studies have focused on amphiphilic polyeletrolytes loaded with a low amount of hydrophobic chromophores. 

Laser-induced fluorescence has proven to be the key to these pioneering studies of transuranic hexafluoride electronic state photophysics and photochemistry. This is a research area of unique opportunity in which fundamental and technical research interests strongly converge. 

In a recent study, poly(aryl ether) dendritic branches terminated with triethyleneglycol chains were attached to Cgg [66] dendrimer 32 represents the fourth generation. The photophysical properties of these fullerodendrimers have been systematically investigated in three solvents, namely toluene, dichloromethane, and acetonitrile. On increasing dendrimer generation, it has been found that in each solvent (i) the maximum of the fullerene fluorescence band is red-shifted... 

Dendritic hosts can be used in aqueous solution to encapsulate water-soluble fluorescent probes. Changes in the photophysical properties of these encapsulated probes are useful to understand the properties of the microenvironment created by the dendritic interior. For example, adamantyl-terminated poly(pro-pylene amine) dendrimers from the first to the fifth generation (36 represents the third generation) can be dissolved in water at pH<7 in the presence of -cyclodextrin because of encapsulation of the hydrophobic adamantyl residue inside the /1-cyclodextrin cavity and the presence of protonated tertiary amine units inside the dendrimer [72]. Under these experimental conditions, 8-anifi-... 

The validity of the above conclusions rests on the reliability of theoretical predictions on excited state barriers as low as 1-2 kcal mol . Of course, this required as accurate an experimental check as possible with reference to both the solvent viscosity effects, completely disregarded by theory, and the dielectric solvent effects. As for the photoisomerization dynamics, the needed information was derived from measurements of fluorescence lifetimes (x) and quantum yields (dielectric constant, where extensive formation of ion pairs may occur [60], the observed photophysical properties are confidently referable to the unperturbed BMPC cation. Figure 6 shows the temperature dependence of the... 

Doose, S., Tsay, J. M., Pinaud, F. and Weiss, S. (2005) Comparison of photophysical and colloidal properties of biocompatible semiconductor nanocrystals using fluorescence correlation spectroscopy. Anal. Chem., 77, 2235-2242. 

Keywords Fluorescence quenching, Nucleobase, Photophysics, Photochemistry, Quantum Chemistry,... 

The photophysical properties of adenine have intrigued chemists from early on. Broo studied adenine and 2-aminopurine (2AP) in order to understand their differences in photophysical properties. Adenine like all natural nucleobases has very short excited state lifetimes and low quantum yields of fluorescence, while 2AP, which differs from adenine in the position of the amino group, has long lifetimes and strong fluorescence, making it a very useful fluorescent probe. In Broo s work it was observed that the first excited state is a nn at vertical excitation but crosses with an nn state which becomes the Si state adiabatically at the minimum. The large out-of-plane distortion on the nn state opens up a deactivation channel in adenine compared to 2AP. In 2AP, on the other hand, the Si state always has a 7T7r character. 

A question that becomes obvious at this point is what happens to the molecules that have similar structures to the natural bases but have different photophysical properties, i.e. they fluoresce. These molecules have similar main structure to the bases, similar ring systems and double bonds, and so, according to the previous discussion, similar conical intersections should be expected. If that is true, and conical intersections facilitate efficient radiationless decay, why do these molecules fluoresce instead of decaying nonadiabatically That is a question that has occupied a number of scientists and some answers and insights are given in the following section. 

Mennucci B, Toniolo A, Tomasi J (2001) Theoretical study of the photophysics of adenine in solution tautomerism, deactivation mechanisms, and comparison with the 2-aminopurine fluorescent isomer. J Phys Chem A 105 4749... 

In a recent evaluation of this phenomenon, the whiteness indices given by eleven individual brighteners on polyester were compared with those of their binary mixtures in various ratios. In many cases the whiteness performance of a mixture was markedly superior to that shown by the individual components [57]. A more specific investigation was confined to a series of benzoxazole FBAs. Their fluorescence spectra and fluorescence lifetimes were determined individually and in mixtures. The relationships between molecular structure and photophysical properties were discussed [58]. 

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. 

Photophysics and Spectroscopy of Fluorophores in the Green Fluorescent Protein Family. 347... 

Their distinguishing feature is the high speed of response. This response develops on the scale of fluorescence lifetime of photophysical or photochemical events that provide the response and can be as short as 10 x-10 10 s. Because of that, the fluorescence reporting is never time-limiting, so that this limit comes from other factors, such as the rate of target - sensor mutual diffusion and the establishment of dynamic equilibrium between bound and unbound target. 

Abstract Fluorescent molecules have been widely used as biomolecular labels, enzyme substrates, environmental indicators, and cellular stains and thus constitute indispensable tools in chemistry, physics, biology, and medicinal sciences. The large variation in the photophysics of the available fluorophores connected with chemical alterations give fluorescent probe techniques an almost unlimited scope for the detection of specific molecules and the investigation of intermolecular interactions on a molecular scale. 

Saito Y, Hanawa K, Kawasaki N et al (2006) Acridone-labeled base-discriminating fluorescence (BDF) nucleoside synthesis and their photophysical properties. Chem Lett... 

The quantum yields are 0.15-0.21 in ethanol and 0.01-0.02 in an aqueous medium, but in micelles, the quantum yields are five to tenfold increased. The aggregation of these dyes was studied in [53]. The amphiphilic squaraines 4 combine favorable photophysical properties and good solubility in aqueous media and in addition interact efficiently with micelles, and therefore have the potential to be used as NIR fluorescent sensors. However, our own investigations show that aniline-based squaraines lack chemical and photochemical stability when compared to oxo-squaraines with heterocyclic end-groups. 

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