Monolayer assemblied incorporating two types of cyanine dyes : possibility of formation of an amalgamation-type J-aggregate

Abstract

The J-aggregates of four types of cyanine dyes-5,6,5',6'-dibenzo-1,1'-diethyl-2,2'-cyanine chloride (Dye I), 5,5'-dichloro-3,3'-diethyl-9-phenyl-thiacarbocyanine chloride (Dye II), 3,3'-dimethyl-9-phenyl-4,5,4',5'-naphthothiacarbocyanine chloride (Dye III), and 1-methyl-1'-octadecyl-2,2'-cyanine perchlorate (S120)-in monolayer assemblies have been fabricated. Mixed assemblies, donor/acceptor, which incorporate two types of cyanine dyes in the same layer plane, are classified into four groups according to the structure of the mixed aggregate ; separate aggregate, mosaic aggregate, homogeneous aggregate of persistence type, and homogeneous aggregate of amalgamation type. Spectroscopic properties of the Dye II/Dye III assembly are completely different from those of the Dye I/Dye II assembly and the S120/Dye I assembly. A single J-band and a single peak of resonance fluorescence in the Dye II/Dye III assembly, in contrast to two J-bands and two peaks of resonance fluorescence in the other assemblies, suggest that the Dye II/Dye III assembly can form an amalgamation-type J-aggregate. An empirical parameter, Δ DA /T DA , introduced to visualize the electronic requirement for the formation of the amalgamation-type J-aggregate, is examined.