Alkyl substituted 2,2'-diquinolines and alteration of their spectrophotometric constants following copper (I) chelation

A study has been made of 10 substituted 2,2'-diquinolines together with their physical constants involving maximum and minimum wavelengths of absorption and associated molecular extinction coefficients. An attempt has been made to interpret the results in relation to the π-electron distribution brought about by substitution of methyl or phenyl groups for hydrogen. The known proficiency of the phenyl groups as an electron donor as compared with the lesser tendency provided by the methyl alkyl group, previously clearly shown in the case of similar substitutions in 1,10-phenanthroline, has been found to apply in the case of 2,2'-diquinoline. The study of mono- and di-substitutions in the 3,4- and 4,4'-positions in 2.2'-diquinoline have been included. It is thought that a better understanding has been attained of the factors influencing structural modifications in the parent molecule which would be worthy of consideration in the case of future attempted developments. The most efficient diquinoline yet described, namely, 4,4'-diphenyl-2,2'-diquinoline (molecular extinction coefficient 9020, wavelength of maximum absorption 559 mμ), was obtained following the disclosed principles of structure.