Guests fluorescent

Addition to such fluorescent dendrimers of non-fluorescing guest compounds capable of interacting with the hetero atoms of the dendrimer - Cu2+ or Co2+ ions in the simplest case - leads to (partial) quenching of fluorescence. A specific example of such behaviour will be found in Section 6.23.3. 

Fluorescence titration measurements are based on the proportion of fluorescence intensity to fluorophore concentration (concentration of fluorescent species in solution this is often a fluorescent guest, G). For a 1 1 complex with host, H, with stability constant Ku = [HG]/[H] [G] the fluorescence intensity Fis given by ... 

A simple plot of FJF against [H] from titration of the quenching host into a guest solution should yield a straight line of slope Kn. Common fluorescent guests such as 8-anilino-l-naphthalenesulfonate (ANS, 1.7) may be used to probe complexation ability of various hosts in this way. 

Dalgarno, S. J., Tucker, S. A., Bassil, D. B., Atwood, J. L., Fluorescent guest molecules report ordered inner phase of host capsules in solution. Science 2005, 309, 2037-2039. 

Figure 11.17 Model showing the FRET process between pyrenyl donor and perylenyl acceptor in hexameric [4]resorcarene capsules containing benzene guests (reproduced from Reference 16) along with the structure of the fluorescent guest 11.26. 

Figure 11.17. The emission can be used to monitor the kinetics of capsule assembly showing it to be relatively fast under these dilute conditions (capsule half life ca. 10 mins depending on solvent). Addition of methanol to the chloroform solution to disrupt the hexamer assembly also results in loss of the FRET emission. FRET was also observed from the outside to the inside of the cavity using a fluorescent guest 11.26.16...

Figure 3.25 Pyrene butyric acid, a fluorescent guest to study interactions inside a capsule.

Although this work does not focus on the host properties of dendrimers, it is interesting to mention briefly some work that has been done on the covalent functionalization of cyclodextrins with dendritic structures, to yield what can be appropriately described as dendritic cyclodextrins. Early work on this area was reported by Ahern et al. [18], which prepared P-CD derivatives per-functionalized with hydroxyethylamino chains on the 6-deoxy position (primary face). These CDs, considered as dendrimer precursors, showed a modest degree of binding selectivity with fluorescent guests. 

Flink, S. Van Veggel, F. C. J. M. Reinhoudt, D. N. A Self-Assembled Monolayer of a Fluorescent Guest for the Screening of Host Molecules. Chem. Commun. 1999, 2229-2230... 

A prerequisite to apply equation (8) besides c > c, (see above) is the formation of 1 1 complexes. In contrast, 2 1 and nonstoichiometric and other associates can be excluded through a nonlinear arrangement of the values measured according to equation (8). An additional indication for 1 1 inclusion stoichiometry is the appear-ence of two isosbestic points in the fluorescence spectra By an extension of this method the complex constants Kq of other non-fluorescing guests G can be calculated... 

Fig. 7. Molecular d5mamics runs (300 K, CHCI3) of pol3maers (a) 5 and (b) 6 (40 repeat units each, schematically represented in Figure 3). Electroactive guest 8 and fluorescent guest 11 employed to probe binding efficiencies of 5 and 6.

The study of binding by fluorescence spectrometry is performed with the same experimental and data analyses as UV-vis spectrometry. Thus experiments usually involve either a fluorescent host or a fluorescent guest, and the change in fluorescence is monitored at different host/guest ratios. The UV-vis equations described above can easily be adapted to fluorescence to provide the association constant for a binding event. ... 

Microenvironment of the emissive species plays an important part in determining the characteristics of the emission. Thus, it is not surprising that supramolecular associations with luminescent molecules often result in altered emission spectra, or lifetime. This is clearly seen in host molecules with relatively hydrophobic cavities that interact with fluorescent guest molecules. Encapsulation, typically, rigidities the guest molecules within the confines of the cavity, which generally results in an increased emission intensity. In addition, hydrophobic pockets of cyclodextrins may also induce shifts in the emission wavelength. For example, ANS (l-anilino-8-naphthalenesnlfonate) and TNS (6-p-toluidinylnaphthalene-2-sulfonate), which are also known as polarity probes, show remarkable complexation-induced fluorescence intensity increases. ... 

PCPs have emerged as particularly exciting solid materials that effectively couple the features of crystallinity and flexibility. The construction of a unique host-guest cooperative system via the hybridization of a flexible PCP, [Zn2(tere-phthalate)2ted] , with a fluorescent guest oligomer, distyrylbenzene (DSB), was... 

Some remarkable examples are given by inclusion of a variety of fluorescent guests into toroidal-shaped hosts such as cyclodextrins [27, 28]. The inclusion process protects the fluorophore from collisional quenching by the solvent and changes the polarity of the microenvironment, thus inducing both enhancement and... 

Yanai N, Kitayama K, Hijikata Y, Sato H, Matsuda R, Kubota Y, Takata M, Mizuno M, Uemura T, Kitagawa S (2011) Gas detection by structural variations of fluorescent guest molecules in a flexible porous coordination polymer. Nat Mater 10 787-793 Hirai K, Furukawa S, Kondo M, Meilikhov M, Sakata Y, Sakata O, Kitagawa S (2012) Targeted functionalisation of a hierarchically-structured porous coordination polymer crystal enhances its entire function. Chem Commun 48 6472-6474... 

NMR techniques, mainly if supported by suitable line simulation procedures, can provide direct information on the dynamics of guest molecules in co-crystalline phases [122-126], Additional information on host-guest interactions for SPS co-crystalline phases, presenting fluorescent guest molecules, can be obtained by fluorescence depolarization measurements [127-129],... 

In this review, only results relative to co-crystalline materials exhibiting fluorescent guests, photoreactive guests (possibly suitable for optical memories), and polar guest (possibly suitable for nonlinear optics and ferroelectric-ity) will be briefly reviewed. 

Fluorescent Guests Transparent films exhibiting polymer/chro-mophore co-crystalline phases have been prepared by simple procedures on SPS, thus achieving low chromophore diffusivities [128,146,147]. 

Tarallo, O., Retraccone, V., Venditto, V., Guerra, G. Crystalline structures of intercalate molecular complexes of syndiotactic polystyrene with two fluorescent guests 1,3,5-Trimethyl-benzene and 1,4-dimethyl-naphthalene. Polymer, 47, 2402-2410 (2006). 

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