Understanding the Spectroscopic Properties and Aggregation Process of a New Emitting Boron Dipyrromethene (BODIPY)

Aggregation of organic dyes often has consequences on their spectroscopic properties in materials. Here, we study a new sterically hindered boron-dipyrromethene (BODIPY), with adamantyl moieties grafted for the first time on the BODIPY core. Its aggregation behavior was investigated in poly(methyl methacrylate) (PMMA) and on drop-casted films by monitoring absorption, fluorescence emission, relative quantum yield (Phi(Flou,Rel)), lifetime and time-resolved anisotropy. Aggregates only appear from 0.067 mol.L-1. A multicomponent analysis demonstrated that the aggregation process can be described by three distinguishable components which correspond to a monomer species (M) and J and H aggregates. The results also indicated a concentration frontier: when the dye concentration increased up to 0.29 mol.L-1, the concentration of M decreased in favor of the aggregates. (Phi(Fluo,Rel) is yet only divided by 5 compared to the dye in solution. Above 0.29 mol.L-1, an equilibrium between M and the J aggregates is established, showing meanwhile a steady Phi(Fluo,Rel). The J aggregates are found to be dimers, whereas the aggregation number is varying for the H aggregates. Analysis of fluorescence and anisotropy decays showed that the excitation energy was transferred from M to the J dimers, and very probably trapped by H aggregates.