Rhodamine absorption spectrum

The rhodamine B-bound complex of Ir1 (387) shows only minor alterations in the absorption spectrum of bound rhodamine B as opposed to free dye however, its fluorescence is strongly quenched.626 Fluorescence is intense when the rhodamine dye is attached to an Ir111 center. The authors conclude that the excited-state quenching mechanism is via electron transfer. 

A different strategy for measuring protease activity is based on the property of xanthene dyes to form H-type dimers (see Sect. 6.2.3) when they are in close proximity. These dimers are accompanied with a characteristic quenching of their fluorescence and, particularly for rhodamines, with a blue shift in the absorption spectrum [121, 122]. The probe D-NorFES-D designed to measure activity of elastase in HL-60 cells consists of an undecapeptide derivatized with one tetramethylrhodamine dye on each side. The sequence contains proline residues to create a bent structure and bring the two fluoro-phores in close proximity. Intact D-NorFES-D shows 90% of its fluorescence quenched plus a blue shift of the absorption spectrum. After addition of the serine protease elastase, an increase in the fluorescence and a bathochromic shift of the absorption spectrum is observed, resulting in an increase in the emission ratio [80],... 

Since the same dye molecules can serve as both donors and acceptors and the transfer efficiency depends on the spectral overlap between the emission spectrum of the donor and the absorption spectrum of the acceptor, this efficiency also depends on the Stokes shift [53]. Involvement of these effects depends strongly on the properties of the dye. Fluoresceins and rhodamines exhibit high homo-FRET efficiency and self-quenching pyrene and perylene derivatives, high homo-FRET but little self-quenching and luminescent metal complexes may not exhibit homo-FRET at all because of their very strong Stokes shifts. 

The occurrence of processes 1) and 2) is at once evident from the observation of the sensitized hole current in an organic crystal with an excitation spectrum closely resembling the absorption spectrum of the dye and with a linear dependence on the light intensity. Fig. 25 shows the identity (except for a slight red shift) of the absorption spectrum e of the rhodamine monomer with the excitation spectrum of the corresponding sensitized current j of a 10-eM solution at phenanthrene. 

The fluorescence polarization spectrum of Rhodamin B and the SoFresponding absorption spectrum are given in the Figure 4.17B. The transition in bands 1 and 5 have the same polarization direction, bands 3 pud 4 are polarized almost perpendicular to 1 and the polarization of 2 gjt at some intermediate angle. These reflect the relative orientation of phe transition moments in the respective bands. 

B. Fluorescence polarization spectrum and absorption spectrum of Rhodamin B. 

Fluorescence resonance energy transfer (FRET) is a technique that has been used to measure distances between pairs of proximal fluorochromes. A suitable pair consists of a donor fluorochrome, which has an emission spectrum that significantly overlaps with the absorption spectrum of an acceptor fluorochrome (2). With the availability of monoclonal antibodies to many cell-surface determinants, intramolecular distances between nearby epitopes and intermolecular distances between adjacent cell-surface macromolecules can be investigated to analyze molecular interactions influencing important cellular events. Such monoclonal antibodies can be conjugated to fluorescein-isothiocyanate (FITC) as the donor, and either tetramethyl-rhodamine-isothiocyanate (TRITC) or phycoerythrin (PE) as the acceptor. 

FITC is excited at 490 nm and emits light at 520 nm. Rhodamine has an absorption maximum at 550 nm, and emits at 580 nm. Figure 7.8(b) shows the overlap between the emission spectrum of FITC and the absorption spectrum of rhodamine. 

Fig. 10.8 Excitation spectra of the sensitized photocurrent for rhodamine-B (10 M) in 1 N KCl solution (dashed line without dye) a) p-GaP b) n-GaP c) absorption spectrum. (After ref. [20])...

Figure 1. The emission spectrum of rhodamine 6G excited at 480 nm and the absorption spectrum of rhodamine B in aqueous solutions of PA-I8K2 0.01 g/L). The dashed line is the emission spectrum of rhodamine B excited...

For temperature measurement by single-dye fluorescence, the temperature sensitivity of a dye, specifically its quantum efficiency, effectively defines the temperature resolution of the measurement itself. Rhodamine B is the most common temperature-dependent fluorescent dye used in both macro- and microscale liquid applications because of its relatively strong temperature sensitivity of 2.3 % in water over a temperature range of 0-120 °C. This dye is also soluble in many other organic solvents, like ethanol, making it a practical choice in a variety of microfluidic applications. Moreover, its absorption spectrum is rather broad (470-600 nm with a peak at 554 nm), meaning it can be readily excited with conventional illumination sources like mercury-arc lamps as well as argon-ion (continuous) and Nd YAG (pulsed) lasers. Further, its emission spectrum is also... 

Fig. 4 UV-vis absorption spectrum of rhodamine-B without zinc ferrite (a) and with the addition of 10 mg zinc ferrite calcined at 800°C (b) after 120 min photocatalytic reaction...

Examples of such continuous absorption and emission line profiles are the optical dye spectra in organic solvents, such as the spectrum of Rhodamine 6G shown in Fig. 3.25b, together with a schematic level diagram [108]. The optically pumped level Ei is collisionally deactivated by radiationless transitions to the lowest vibrational level Em of the excited electronic state. The fluorescence starts therefore from Em instead of Ei and ends on various vibrational levels of the electronic ground state (Fig. 3.25a). The emission spectrum is therefore shifted to larger wavelengths compared with the absorption spectrum (Fig. 3.25b). 

The spectral properties of these derivatives are similar to native rhodamine. The excitation maximum occurs at about 543 nm and its emission peak at 567nm, producing light in the orange-red region of the spectrum. The extinction coefficient of tetramethylrhodamine-5-(and-6)-iodoacetamide in methanol at its wavelength of maximum absorptivity, 542 nm, is 81,000M-1cm-1. 

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