Fluorescent sensors, molecular wires

Figure 9.3 Comparison of conventional fluorescent chromophore sensors versus the molecular wire response of the AFP.

The predictive power of the luminescent PET sensor principle is again apparent here. Further, the benzocrown ether and the amine receptors would selectively bind Na" and H, respectively. A remarkable feature here is that no molecular wiring is needed to allow the human operation of this two-input molecular device. The device self-selects its own ion inputs into the appropriate signal channels by means of the chemoselective receptor modules. Since the output signal is fluorescence, even a single molecule can interface with detectors in the human domain, including the dark-adapted eye. Tanaka s 45 is another example where fluorescence quenching is achieved only when Ba and SCN are present. This was mentioned in Section 6. Similarly, several sensor systems—1,17, and 21—could be employed... 

Building onto the concept of molecularly wired sensors for signal amplification, Swager reported in 1998 the synthesis of a series of porous PPE derivatives in which pentiptycene modules are incorporated into the PPE main chain. The incorporation of the pentypticene moieties makes 29 and 30a (Chart 5) efficient solid-state emitters unaffected by aggregation i.e., their emission spectra in solution and in the solid state are almost identical. The authors found that thin films of these highly fluorescent PPEs are excellent sensors for the detection of trinitrotoluene and dinitrotoluene. Both aromatics suppress the fluorescence of 29 or 30a effectively but reversibly. The headspace, i.e., the atmospheric volume above land mines, contains measurable quantities of dinitrotoluene. As a consequence, polymers 29 and 30 coated on top of a fiber optic sensor will allow their simple detection by these very sensitive molecular wire-type materials. This elegant concept should be extendable and applicable to any other analyte, (a) which has the ability to quench fluorescence and (b) for which a receptor can be attached to PPEs. 

Fluorescence Sensing of Anions, p. 566 Fluorescent Sensors, p. 572 Molecular Logic Gates, p. 893 Molecular Squares, Boxes, and Cubes, p. 909 Molecular Switches, p. 917 Molecular Wires, p. 925 Molecular-Level Machines, p. 931 Photochemical Sensors, p. 1053 Rotaxanes and Pseudorotaxanes, p. 1194 Self-Assembling Catenanes, p. 1240 Self-Assembly Definition and Kinetic arid Thermodynamic Considerations, p. 1248... 

---