Absorption spectra spectral change

A broad absorption spectrum of t,t,t-TPCB" was observed at 77 K, at 400-670 nm with a peak at 480 nm, and collapsed without any particular spectral change upon warming up to 90 K (Fig. 4). However, the spectrum changed to have clear peaks at 485 and 780 nm upon photoirradiation at 77 K (Fig. 4a). The absorption spectrum then changed to have a peak at 550 nm upon warming. The difference spectrum, obtained by subtracting the spectra both before and after warming, clearly indicates the collapse of the peak at 485 nm and the formation of bands at 370, 550, and 770 nm (Fig. 4b). 

Fig. 8.4 Absorption spectrum of dinoflagellate luciferin, and the spectral changes caused by luminescence reaction after the addition of luciferase, in 0.2 M phosphate buffer, pH 6.3, containing 0.1 mM EDTA and BSA (O.lmg/ml) (Nakamura et al., 1989). Reproduced from Hastings, 1989, with permission from the American Chemical Society and John Wiley Sons Ltd.

The electronic spin-state crossover in [Fe(HB(pz)3)2] has also been observed in the fine structure of its fC-edge x-ray absorption spectrum [38]. The changes in the x-ray absorption spectra of [Fe(HB(pz)3)2] are especially apparent between 293 and 450 K at ca. 25 eV, as is shown in Fig. 5. The 293 K x-ray absorption spectral profile observed in Fig. 5 for [Fe(HB(pz)3)2] has been reproduced [39] by a multiple photoelectron scattering calculation, a calculation that indicated that up to 33 atoms at distances of up to 4.19 A are involved in the scattering. As expected, the extended x-ray absorption fine structure reveals [38] no change in the average low-spin iron(II)-nitro-gen bond distance of 1.97 A in [Fe(HB(pz)3)2] upon cooling from 295 to 77 K. 

Figure 12. Spectral change of the annealed film by moisture treatment, (a) CgAzoCioN+Br film was sealed in a quartz cell with 62% humidity after annealing. The type V spectrum (broken line) immediately moved to the type VI spectrum and then shifted to the type I absorption, (b) Humidity effect on time courses of the spectral change. Ao and A, are absorbance of 370 nm immediately and l min after stored in a sealed quartz cell, respectively.

In principle, the problems of intensity-based sensing can be avoided using wavelength-ratiometric probes, i.e., fluorophores that display spectral changes in the absorption or emission spectrum on binding or interaction with the analytes (Figure 1.1). In this case, the analyte concentration can be determined independently of the probe concentration by the ratio of intensities at two excitation or two emission wavelengths. 

Another explanation for their resonance Raman results could be a change in the zwitterionic nature of the merocyanine isomers in the different solvents which may result in changes in the Raman transition probabilities, or the spectral changes could be due to solvent shifts of the absorption spectrum, resulting in a change in the relative contribution of the different vibrational modes to each resonance Raman spectrum. We note that in the same article, the authors report the transient absorption spectra of the merocyanine forms, which clearly show that the BIPS spectrum in cyclohexane has more discrete vibrational modes than are observed in the polar solvents, which show more spectral broadening. Al-... 

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