Synthesis and properties of barbiturate indolenine heptamethinecyanine dyes

Indolenine and benzindolenine heptamethinecyanine dyes having barbiturate at meso position were synthesized by the substitution of corresponding meso chloro substituted dyes with barbituric acid, and their absorption spectra and crystal structures were investigated. All barbiturate dyes had absorption near 800 nm and showed hypsochromic shift from the corresponding chloro dyes. Both barbiturate and chloro benzindolenine dyes showed bathochromic shift from the corresponding indolenine dyes. The crystal structures of barbiturate dyes indicated that barbiturate ring is sterically hindered by indolenine ring and cannot form adequate π-conjugation with cyanine main chromophore.