Quinolinium zwitterion

The spectra of the pyridinium and quinolinium analogues are superimposed in Figure 2 to show three photochromic bands with exploitable maxima at 495, 565 and 614 nm. The absorption maximum at 495 nm of the pyridinium zwitterion corresponds to minima in the spectra of the other materials whereas the maxima at 565 and 614 nm of the quinolinium zwitterions only partially overlap the adjacent charge transfer bands. The fact that there... 

Alkaline hydrolysis of 6-methoxy- 4-methoxycarbonyl-2-methyl-tbiopyrimidine leaves unaffected only the methylthio group which can then be hydrolyzed in acid. 9-Alkylthioacridines are hydrolyzed by acid less readily than the corresponding alkoxy compounds and more readily than alkylamino derivatives. Peculiarly, a better yield of the amine results from 4-thioxo than from 4-methylthio-quinazoline on heating with primary amines. Displacement in 2-methylthio-quinolinium and 3-methylthiopyridazinium compounds (137) proceeds readily with the carbanion of diethylmalonate or the zwitterion of 2-methylbenzothiazolinium derivatives. 

It is believed that the ground state of 11 is very polar and zwittewrionic, T-D+-7r-A , while its first excited state T-D-tt-A is less polar. (Here, T is the alkyl tail ). In 11, the quinolinium and tricyanoquinodimethanide rings may be twisted by some angle 0 (0 = 30° for the similar zwitterion 22 ) because of steric hindrance. The neutral excited state T-D-tt-A might be more planar (0 0°) if 0 90° then IVT = 0, and the blue color must disappear. 

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