Anthracene fluorophore

Fluorescent molecule (1) (Figure 6.5) acts as a host for Ca2+ ions. On addition of Ca2+ ions, the flexible polyether chain folds, leading to stacking of the anthracene fluorophores, and monomer emission is replaced by excimer emission. 

Figure 6.20 Action of a fluorescent PET potassium cation sensor as a molecular switch using a macrocyclic electron donor and anthracene fluorophore...

Fabbrizzi s S[36] is unusual in using a nonmetallic, redox-active guest with a metal center serving as the receptor. An anionic nitrobenzoate guest is held by coordination of the carboxylate to the free apical position in Zn2+. The electron-deficient nitrobenzoate engages in PET with the anthracene fluorophore to switch the fluorescence OFF . 

Figure 17 A pictorial view of the mechanism by which Zn" induces quenching of anthracene fluorescence of three-component system 11. On coordination to the metal centre, the N,W-dimethylaniline subunit and anthracene fluorophore are brought close enough to allow a through-space eT process to take place.

This system has been improved upon in compound 2 (Fig. 3) in which both receptors are more proximal to the anthracene fluorophore [10]. This compound exhibits a binary response, i.e., in the absence of both, or in the presence of only one of the two stimuli, there is no fluorescence whatsoever, whereas the presence of both inputs results in a bright fluorescence with (j>P = 0.24. 

We focus on three-input AND gate 4 to illustrate the concepts discussed above, though there are newer cases aimed at more biological targets. Compound 4 possesses three receptors which select Na", H" ", and Zn + as inputs. Benzo-15-crown-5-ether, tertiary amine, and phenyliminodiacetate are the three receptors. Each of these receptors is a PET donor toward the anthracene fluorophore. In that sense, 4 is a conceptual continuation of 3. Again, fluorescence enhancement is seen only when all three PET processes are knocked out. Table 1 details the numbers involved. 

As a specific example, we can consider H+-driven YES and PASS 1 logic gates 5 and 6, respectively, both of which carry the same fluorophore, that is, the same excitation and emission colors. However, tag 5 switches on its fluorescence as pH is reduced to low values while 6 shows pH-independent fluorescence. This is the distinction between the two tags. Many other distinctions, that is, other Boolean logic actions, can be built up in similar ways. The different pH-dependent fluorescence behavior of 5 and 6 arises from the presence of the tertiary amine receptor in 5 and its absence in 6. As seen in the previous sections, the amine is the donor component in the PET process whereas the anthracene fluorophore serves as the acceptor. Thus, fluorescence is minimal in neutral solutions, but under... 

Compound 18 contains an anthracene fluorophore and a methylene spacer, as well as a 2,2 -bipyridyl receptor which can bind either H+ or Zn +. Either of these two binding events makes the 2,2 -bipyridyl unit a better electron acceptor because of its positive charge and its enforced planarityTherefore, a PET process becomes possible from the anthracene fluorophore to the bound 2,2 -bipyridyl receptor. The fluorescence output is therefore quenched in the presence of either input or both. The truth table (Table 5) shows how this leads to NOR logic. 

The sensing of potential pollutants has led to the development of 23, which can distinguish elegantly between Cd(ll) and Zn(n) but due to similar affinity of many receptors, it has been difficult to achive such selectivity to date." On the basis of the use of iminodiacetate receptors connected to an anthracene fluorophore by covalent methyl spacers, the sensor was found to be highly water soluble where the fluorescence was switched off between pH 3 and 11, owing to PET quenching of the anthracene excited state by the receptor. On Zn(ll) titration, a broad, red-shifted emission occurred, centered at 468 nm however, in the presence of Cd(II), a red-shifted emission was observed, centered at... 

PET donor to the anthracene fluorophore. The PET process from the amine unit can be stopped by protonation as usual. Another PET process from the TTF unit stops after it is selectively oxidized to its dication form. Even then, the PET process from the anthracene to the dicationic TTF unit is apparently prevented only by the Marcus inverted region. The redox reactions of the TTF unit can also be induced by chemical oxidants like Fe(C104)3. 

Calero P, Martinez-Manez R, Sancenon F, Soto J (2008) Synthesis, characterisation and optical properties of silica nanoparticles coated with anthracene fluorophore and thiourea hydrogen-lxHiding subunits. Eur J Inorg Chem 5649-5658... 

Wang and co-workers have also prepared diboronic acid systems with two anthracene fluorophores with variable spacers (29a-j) [81, 82]. They demonstrated that 29e is selective for Sialyl Lewis X [81] and that 29f is selective for D-glucose [82]. Observed Xjpp for 29f were 34 for D-fructose, 30 for D-galactose and 1472 for D-glucose in 1 1 (v/v) methanol-water at pH 7.4 (phosphate buffer). 

Fig. 6.16 Potassium cation sensor as a molecular fluorescence switch in a PET process of anthracene fluorophore having a macrocyclic donor unit...

Valeur B, Rempp P, Mormerie L (1974) Insertion of anthracene fluorophore in polystyrene chain—study of local movements via inhibition and fluorescence polarization. C R Hebd Seances Acad Sci Ser C 279(25) 1009-1012... 

In host guest chemistry, anthracene fluorophore is of special interest in both inorganic and biological systems, because of its availability, derivatization, and fluorescence sensitivity [47]. Numerous anthracene-appended calix[4]arene hosts have been developed for the fluorogenic recognition of cations and anions. 

---