Fluorescent absorption and emission

Bestvater F. Spiess E, Stobrawa G, Hacker M, Feurer T, Porwol T, Berchner-Pfannschmidt U, Wotzlaw C, Acker H (2002) Two-photon fluorescence absorption and emission spectra of dyes relevant for cell imaging. J Microsc 208 108-115... 

In the case of substances whose structures are pH-dependent (e.g. phenols, carboxylic and sulfonic acids, amines etc.) it is possible to produce fluorescences or make them disappear by the deliberate manipulation of the pH [213] (Table 20). Shifts of the positions of the absorption and emission bands have also been reported. This is particularly to be observed in the case of modified silica gels, some of which are markedly acidic or basic in reaction (Table 25). 

Absorption and emission spectra of six 2-substituted imidazo[4,5-/]quinolines (R = H, Me, CH2Ph, Ph, 2-Py, R = H CH2Ph, R = Ph) were studied in various solvents. These studies revealed a solvent-independent, substituent-dependent character of the title compounds. They also exhibited bathochromic shifts in acidic and basic solutions. The phenyl group in the 2-position is in complete conjugation with the imidazoquinoline moiety. The fluorescence spectra of the compounds exhibited a solvent dependency, and, on changing to polar solvents, bathochromic shifts occur. Anomalous bathochromic shifts in water, acidic solution, and a new emission band in methanol are attributed to the protonated imidazoquinoline in the excited state. Basic solutions quench fluorescence (87IJC187). 

Quantitative accuracy and precision (see Section 2.5 below) often depend upon the selectivity of the detector because of the presence of background and/or co-eluted materials. The most widely used detector for HPLC, the UV detector, does not have such selectivity as it normally gives rise to relatively broad signals, and if more than one component is present, these overlap and deconvolution is difficult. The related technique of fluorescence has more selectivity, since both absorption and emission wavelengths are utilized, but is only applicable to a limited number of analytes, even when derivatization procedures are used. 

Steady-State Fluorescence Depolarization Spectroscopy. For steady state depolarization measurements, the sample is excited with linearly polarized lig t of constant intensity. Observed values of P depend on the angle between the absorption and emission dipole moment vectors. In equation 2 (9), Po is the limiting value of polarization for a dilute solution of fluorophores randomly oriented in a rigid medium that permits no rotation and no energy transfer to other fluorophores ... 

Poly(aryl ether) branches of generation 1 to 3 have been appended to a pho-totautomerizable quinoHne core to investigate the effect of dendritic architecture on the excited state intramolecular proton transfer [45]. The changes observed in the absorption and emission spectra on increasing dendrimer generation indicate that the dendritic branches affect the planarity of the core and therefore the efficiency of the excited state intramolecular proton transfer and of the related fluorescence processes. 

Absorption and Emission Spectra. The excitation-emission spectrum of 1 (bottom half of Fig. 1) shows that the relatively narrow emission band is nearly independent of the excitation wavelength and that the excitation spectrum is not only nearly independent of the wavelength at which the emission is monitored, but is also very similar to the absorption spectrum, both being somewhat broader than the emission band. This leaves no doubt that the observed emission is due to the polysilane, and its shape, location and the mirror image relation to the absorption permit its assignment as fluorescence. 

The general principle of detection of free radicals is based on the spectroscopy (absorption and emission) and mass spectrometry (ionization) or combination of both. An early review has summarized various techniques to detect small free radicals, particularly diatomic and triatomic species.68 Essentially, the spectroscopy of free radicals provides basic knowledge for the detection of radicals, and the spectroscopy of numerous free radicals has been well characterized (see recent reviews2-4). Two experimental techniques are most popular for spectroscopy studies and thus for detection of radicals laser-induced fluorescence (LIF) and resonance-enhanced multiphoton ionization (REMPI). In the photochemistry studies of free radicals, the intense, tunable and narrow-bandwidth lasers are essential for both the detection (via spectroscopy and photoionization) and the photodissociation of free radicals. 

Figure 2.8. Absorption and fluorescence spectra of 9-anthramide. Note the symmetry of the absorption and emission. Reproduced with permission from Ref. 8.

This method is perfectly suitable for low concentrations of fluorescent materials. However, in order to study factors which affect the fluorescence quantum yield, such as molecular association or photochemical reactions, much higher concentrations than can be used in the right-angle fluorescence method are required. This follows from the fact that the 0 - 0 vibrational bands in the absorption and emission spectra often overlap. Therefore at relatively high concentrations light emitted at these overlapping wavelengths will be reabsorbed. 

Figure 4. Absorption and emission of TIN and MT in different solvents (I) absorption of TIN in methylcyclohexane/isopentane at 150 K (II) absorption of TIN in ethanol/methanol at 150 K (III) absorption of MT in hexane at 296 K (IV) (a) fluorescence and (b) phosphorescence of TIN or MT in 20 20 1 ethanol/ether/pyridine at 90 K (V) fluorescence of TIN in methylcyclohexane/isopentane at 90 K.

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. 

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