Hypsochromic sensitivity

The scale is based on the solvatochromic behavior of an n — jt electronic transition, so it reflects a high hypsochromic sensitivity to solvent acidity (specific solvation between the lone pair involved in the elecironic transition and solvent acidity is lost when one electron in the pair is electronically excited). An n —> Jt electronic transition is also known to decrease the polarity of the chromophore concerned, so an increase in SPP for the solvent will cause a hypsochromic shift in the elecironic transition. 

Heteroatom-containing derivatives of pentalene and azulene are 8- and 10-jr-electron systems, respectively, and have been extensively studied by Hafner and co-workers.301-304 A few examples are presented in Schemes 30, 47, and 86. Electron-rich azapentalenes 247—249305 306 and various aza-azu-lenes 250—252300-302 have intense colors and are stable but oxygen-sensitive compounds. Azulenes with nitrogen heteroatoms placed in positions with high electron density, such as position 5, or positions 5 and 7, present a hypsochromic effect, while a heteroatom in position 6, with low electron density, exerts a bathochromic effect. When both types of positions are substituted by heteroatoms, their effect is canceled out.307 The bond lengths in 252 (Scheme 86), as determined by X-ray, indicate delocalization as in 252a and 252b.308 309... 

The probe was selective for potassium determination no significant fluorescence signal was observed with other metals. However, Na+ andLi+ induced a hypsochromic shift of the absorbance maximum in the NIR dye in free solution. Although the NIR dye offered some selectivity for potassium in analysis, the selectivity was enhanced further by the polymer matrix. Furthermore, the sensitivity of the probe to KOH and KCI was almost identical. This may indicate that the sensor response was not influenced by a pH change or the presence of anions. The fluorescence response of the immobilized NIR dye with KOH and KCI is shown in Figure 7.11. 

Fig. 9. A proton and calcium ion-sensitive XOR gate exemplified by 64. The UV transmittance i of the styrylquinoline chromophore alone has a minimum at 390 nm. ii Addition of protons leads to a bathochromic shift in the transmittance minimum, leading to a high transmittance at 390 nm. Hi The minimum is shifted hypsochromically through addition of calcium ions, resulting in a high transmittance output at 390 nm. iv The position of the minimum is not affected greatly by the presence of both stimuli, leading to a low transmittance output, mimicking the behavior of an XOR gate...

A new simple and reliable method for monitoring photoinduced acid generation in polymer films and in solutions of the kind used in 193 nm and deep-UV lithography was developed. By using N-(9-acridinyl)acetamide, a fluorescent acid-sensitive sensor, we have been able to study the effects of trifluoroacetic acid and photoacids generated from triphenylsulfonium hexafluoroantimonate on the spectral properties of the acid sensor in THF solution and in alicyclic polymer resist films exposed at 193 nm. In both cases a hypsochromic spectral shift and an increase in fluorescence intensity were observed upon protonation. This technique could find application in the study of diffiisional processes in thin polymer films. 

Probe 34 (Fig. 28.8), a calix[4]biscrown-6 ether conjugated with BODIPY units, exhibits high selectivity for Cs" among several cations examined [62]. Substitution at the a-position of BODIPY improves the photophysical sensitivity. In the presence of Cs" ions, a hypsochromic shift was observed in the fluorescence and absorption spectra. This shift is due to binding of the crown ether to Cs", which decreased the electron-donating ability of the oxygen atoms. 

---