Ferrocene fluorescence quenching

Figure 5 Plots of log versus AG°et for fluorescence quenching of RAcrH" (2.0 x 10 " M) by various electron donors (a) in MeCN and (b) in benzene at 298 K. Numbers refer to electron donors benzene (1), toluene (2), ethylbenzene (3), cumene (4), ra-xylene (5), o-xylene (6), 1, 3, S-ttimethylbenzene (7),/ -xylene (8), 1,3-trimethylbenzene (9), 1, 2,3,4-tetramethylbenzene (11), 1,2,3,5-tetramethylbenzene (12), 1,2,4,5-tetramethylben-zene (13), pentamethylbenzene (14), hexamethylbenzene (15), triphenylamine (16), N,N-dimethylaniline (17), ferrocene (18), and decamethylferrocene (19). (From Ref. 79.)...

Fluorescence Quenching. The fluorescence intensity (/f) of trans-stil-benes is reduced in the presence of additives such as ferrocene or azulene. For stilbene and several bromostilbenes Saltiel and co-workers studied the effect of fluorescence quenching by azulene [105,295], From linear Stern-Volmer plots (Eq. 10) values of Ks = rskq between 20 and 30 M1 have been obtained (Table 13). 

Stern-Volmer constants of similar size were found for nitro- and cyanostilbenes using ferrocene as quencher [85,118]. Fluorescence quenching by oxygen in saturated solution (1 bar) is small for fram-stilbene [105]. 

A direct demonstration of binding of alcohol to LADH in the absence of coenzyme has been made (253) by utilizing the spectroscopic changes and protein fluorescence quenching that occur when the chromophoric substrate hydroxymethyl ferrocene binds. It was not definitively established, however, that the alcohol binds in the substrate binding pocket. 

Ferrocene has been widely investigated as an electron donor and its electron donating ability can be tuned by redox reactions. As anticipated, when a ferrocene unit is covalently connected to an electron acceptor moiety that shows intrinsic fluorescence, the fluorescence of the acceptor moiety would be largely quenched because of the photoinduced electron transfer between ferrocene and the fluorescent acceptor. For instance, triad 15 that contains perylene diimide flanked by two ferrocene moieties, shows rather weak fluorescence due to the photoinduced electron transfer between perylene diimide and ferrocene units. Either chemical or electrochemical oxidation of ferrocene unit lead to fluorescence enhancement. This is simply because the electron donating ability of ferrocene is reduced after oxidation and accordingly the photoinduced electron transfer is prohibited. In this way, the fluorescence intensity of 15 can be reversibly modulated by sequential electrochemical oxidation and reduction. Therefore, a new redox fluorescence switch can be established with triad 15.25... 

The efficient on/off switching of fluorescence from substituted zinc porphyrin-ferrocene dyads 16a and 16b is achieved through redox control of the excited-state electron transfer quenching.26 This redox fluorescence switch is based on the switching of the excited-state electron transfer from the ferrocene to the zinc porphyrin through the use of the ferrocene/ferrocenium (Fc/Fc +) redox couple. 

Intramolecular single electron transfer occurs within the supramolecular systems (224). " The electron transfer only occurs from the nitrogen function attached to the 4-amino substituent. A comparison between redox potentials and the photophysical behaviour of the phthalimides (225) has been made. Other work dealing with electron transfer in phthalimide systems has examined the behaviour of (226). The singlet excited state of (227) is fluorescent and this can be effectively quenched by ferrocene. ... 

X 10 mol L range, with a detection limit of 0.27 jM. The fluorescence energy transfer between ferrocene donor and porphyrin acceptor was also considered. Nanofibers with distinct luminescent property were fabricated by electrospinning porphyrinated polyimides. The new material demonstrated to be a very interesting sensory material for detection of trace amounts of TNT vapor (10 ppb) [249]. The presence of covalently bonded porphyrin fluorophores in the main chain diminish the aggregation-induced self-quenching of fluorescence and improves the physicochemical stability of the polyimide nanofibers. 

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