Understanding the Spectroscopic Properties and Aggregation
Process of a New Emitting Boron Dipyrromethene (BODIPY)
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Abstract
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 (Φ<sub>Fluo,Rel</sub>), lifetime and time-resolved anisotropy. Aggregates
only appear from 0.067 mol·L<sup>–1</sup>. 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<sup>–1</sup>, the concentration of M decreased in favor of the
aggregates. Φ<sub>Fluo,Rel</sub> is yet only divided by 5 compared
to the dye in solution. Above 0.29 mol·L<sup>–1</sup>,
an equilibrium between M and the J aggregates is established, showing
meanwhile a steady Φ<sub>Fluo,Rel</sub>. 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