Virtual spacer

On examining structure 1, we notice the steric crowding at the link between the tetracarboxylate receptor and the linearly fused tricyclic system. Thus, orthogonalization occurs at this link, making it a virtual spacer. The spatial isolation of the two ji-electron systems allows us to describe the tricyclic unit as the lumophore. The tetracarboxylate receptor also coexists as a clearly distinguishable module. 

Ca2+ sensing by 1 can be understood by considering a PET process originating in the Ca2+-free tetracarboxylate receptor and the linearly fused tricyclic system. The rapidity of the process may be ascribed to the low oxidation potential of the electron rich alkoxyaniline donor and to the short distance of separation between the two transfer components. The minimal separation arranged by a virtual spacer of zero carbon atoms is worthy of note. A low level of luminescence is seen owing to the fast PET. 

Heagy MD. IV-Phenylboronic acid derivatives of arenecarboximides as saccharide prohes with virtual spacer design. In Geddes CD, Lakowicz JR (Eds), Topics in Fluorescence Spectroscopy, Vol. 11. Springer, New York, 2006, pp. 1-20. 

Compound 64 [133] is an ICT fluorophore emitting at 660 nm in THE. The dimethylamino unit in 64 is an electron pushing component in this push-pull 7i-electron system. The addition of t-BuO deprotonates the phenol group and the emission is switched ofF due to PET across the virtual spacer. Upon addition of H, 64 gives a blue-shifted emission at 565 nm due to protonation of the... 

This disadvantage can be ruled out by spacers between the allylic and the acrylic group [15], but the selectivity in favor of the allylic group is not improved. An acetylenic triple bond instead helps to clarify the situation. 2-Propynoxyethyl acrylate, available in 90 % yield from ethoxylated propargylic alcohol by esterification, is hydrosilylated very smoothly only at the triple bond, leaving the acrylic side virtually untouched (Eq. 5). 

The same arsenal of preparative methods has been applied successfully for the corresponding dinuclear derivatives of ethyne HC CH and dialkynes HC C-X-C CH, where X can be virtually any spacer unit.50-52,54 55 57 61 62 71 76-83 As mentioned in the introduction to this chapter, ethyne is readily converted into polymeric explosive AuC=CAu and its complexes (L)AuC=CAu(L), of which the families with L = R3P84 and L = RNC are particularly large (Chapter 7). With the unit X in (L)AuC=CXC=CAu(L) being an alkylidene spacer, flexible complexes are obtained, while with alkenylidene, alkynylidene, or arylidene units,57 rigid molecules (L)AuC=CXC=GA11(L) are generated. Specific examples are presented below in the context with the structural patterns of extended systems. 

Fig. 12 Left. ICT-PET probe 34 with a small and rigid spacer (thick black), decoupling the PET active donor = receptor unit from the 7c-conjugated ICT fluorophore. Middle and right probes 35 and 36 combining a conventional ICT and a virtually decoupled ICT process with two identical receptor units (35, for Hg2+) and two different receptor units (36, tetraoxa monoaza crown for Na+ and dithia monooxa monoaza crown for Ag+). For color code, see Fig. 10...

The most common dimensional measurements relate to the size of test pieces because this information is required for virtually all physical test methods. There is also sometimes need to measure dimensions of components of the apparatus, such as the thickness of spacers in compression set tests. Other aspects of dimensional measurement that are relevant to rubber testing include extensometry, surface roughness, dimensional stability and dispersion. 

VIII. PET SIGNALING SYSTEMS WITH VIRTUAL (Co) SPACERS... 

Lumophore-receptor systems where the two components are sterically held orthogonal can be considered to have a virtual Co spacer between the lumophore and receptor. Thus these systems can be approximately considered as a PET system. A deeper analysis would take twisted intramolecular charge transfer (TICT) states [116] into account whose thermodynamics is, unsurprisingly, very similar to that of PET systems. 

The positive response of 82 offers evidence for the luminescent PET signaling of irreversible interactions. More specifically, it underpins the previously known, but empirically designed, lumophore-spacer-maleimide systems 83 [158] and 84 [159] operating at shorter communication wavelengths. In addition, the present results help to explain the larger thiol-induced fluorescence enhancements found in 85 [160] with unassigned mechanism of action. The latter are twisted lumophore-maleimide systems. Their virtual Co spacers ensure rapid PET rates and, subsequently, low fluorescence quantum yields in the absence of thiol. 

Fouling and Scaling Figure 14.14a shows a feed spacer with foulants adhering to the spacer, while Figures 14.14 b and c show feed spacers virtually completely blocked with foulants and scale, respectively. This... 

Figure 14.14 (a) foulants adhering to feed spacer feed spacers virtually blocked with (b) foulants and (c) scale. 

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