The Impact of Aggregation on the Photophysics of Spiro-bridged Heterotriangulenes.

2020 
We report on the impact of the central heteroatom on structural, electronic, and spectroscopic properties in a series of heterotriangulenes including a spirofluorene-bridged triphenylamine, -phosphine, and -phosphine oxide and provide a detailed study on their aggregates. The in-depth analysis of their molecular structure by NMR spectroscopy and X-ray crystallography was complemented by density functional theory calculations to shed light on the electronic structure. This analysis was particularly helpful to deconvolute the complex fluorescence spectra with contributions from the peripheral fluorenes and the respective heteroaromatic cores. Going beyond the molecular scale, we examined the aggregation behavior of these heterotriangulenes in THF/H 2 O mixtures and analyzed the amount as well as the size of the aggregates by static and dynamic light scattering. The excited-state interactions within the aggregates at high water contents were found to be similar to those found in the solid state. In addition, a plethora of morphologies and superstructures were detected by scanning electron microscopy when the dispersions were drop-casted and dried.
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