Aggregation Behavior and Spectral Properties of BODIPY Luminophors in Langmuir-Schaefer and Poly(Methyl Methacrylate) Thin Films

Abstract

It is known that boron-dipyrromethene (BODIPY) dyes have a remarkable combination of photophysical and photochemical properties in solutions. Unfortunately, these properties are lost in thin films due to aggregation quenching effect (ACQ) and internal filter effect, limiting BODIPY application in optical devices. The introduction of bulky substituents into dye molecule should affect the supramolecular organization of BODIPY in thin films. Therefore, using the example of β-benzyl-substituted complex (1) and bis(BODIPY) dimer (2), we study the influence of bulky substituents at the β, β΄-positions of these BODIPY molecules on their aggregation behavior in mono-and multilayer Langmuir-Schaefer (LS) films. A comparative analysis of BODIPY spectral properties in LS and poly(methyl methacrylate) (PMMA) films has been carried out. It was shown that the presence of bulky benzyl-substituents in β-positions of pyrrole rings promotes the formation of H-and J-type aggregates in multilayer LS-films of the dye 1 and BODIPY dimer 2. The dye 1 predominantly forms H-type aggregates, while for the dye 2, the equilibrium is shifted towards the formation of J-type aggregates. The studied BODIPYs with a low content of up to 1 wt. % exhibit intense fluorescence being included in PMMA films. The results obtained give the possibility to use more efficiently thin-film structures based on the studied BODIPY thin films in optoelectronics.