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 (ΦFluo,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. ΦFluo,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 ΦFluo,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.

有机染料的聚集通常会对其在材料中的光谱特性产生影响。本研究针对一种新型空间位阻型氟化硼二吡咯（boron-dipyrromethene, BODIPY）展开探究，该染料首次在BODIPY母核上接枝了金刚烷基团。我们通过监测吸收光谱、荧光发射光谱、相对量子产率（ΦFluo,Rel）、荧光寿命以及时间分辨各向异性，研究了该染料在聚甲基丙烯酸甲酯（poly(methyl methacrylate), PMMA）基质与滴铸薄膜中的聚集行为。研究发现，该染料仅在浓度达到0.067 mol·L–1时才会形成聚集体。多组分分析结果显示，该聚集过程可通过三种可区分的组分进行描述，分别对应单体物种（M）、J聚集体与H聚集体。研究结果还揭示了一处浓度临界点：当染料浓度提升至0.29 mol·L–1时，单体M的占比逐渐降低，聚集体占比随之提升。与溶液中的染料相比，此时的相对量子产率ΦFluo,Rel仅为其1/5。当浓度超过0.29 mol·L–1时，单体M与J聚集体之间达到动态平衡，此时相对量子产率ΦFluo,Rel保持稳定。研究发现J聚集体为二聚体，而H聚集体的聚集数则存在差异。对荧光衰减与各向异性衰减的分析表明，激发能可从单体M转移至J二聚体，且极有可能被H聚集体捕获。