Electronic Absorption Spectra of New y-Keto-dimethine Cyanine Dyes and Apocyanines

New asymmetrical y-keto-dimethine cyanines (2.-f) were prepared through the condensation of phenyl glycosal derivatives (l.-e) with 2-methyl pyridinium (quinolinium)- 2yl salts. Such dyes were converted into the corresponding dyes (3a-g and 4a-d) by cyclocondensation with hydrazines or hydroxylamine hydrochloride under suitable conditions. The new synthesized cyanines were identified by elemental and spectral analyses. The U\u27V-visible absorption spectra of some selected dyes were investigated in pure and mixed solvents as well as in aqueous buffer solutions. Molecular complex formation with ethanol was verified by mixed solvent studies. Electronic transitions were attributed to either locally excited or predominantly charge transfer states. The spectral shifts were discussed in relation to molecular structure and in terms of medium effects. The variation of absorbance with pR was utilized for the determination of the pK. value for aselected compound (2e). The photostability of some selected đyes (2e, 3g and 4d) was investigated

New cyanine dyes from 4,9-dioxopiperidino[2,3-<i>g</i>]-1 ,2,3,4,6,7,8,9- octahydroquinolino quinone

426-429Symmetrical bis-(styryl, tetramethine, aza-styryl) cyanine dyes (5a-g, 6a-c, 7a-c) containing arylidene, heterylidene and schiff base moieties have been obtained by the interaction of 4,9- dioxopiperidino [2,3-g]-1 ,2.3,4,6, 7 ,8,9-octahydroquinolinoquinone 1 with aromatic aldehyde, heterocyclic aldehyde and nitroso compounds followed by condensation with 2(4)-methyl quaternary salts. The UV spectra in 95% ethanol of all the synthesized cyanine dyes show that the photosensitization of the dyes increases (or decreases) by increasing (or decreasing) conjugation, by the presence of electron donating (attracting) groups and the more (less) planarity of the dyes. The new compounds have been identified by elemental analysis, IR and 1H NMR spectral data