The asymmetric substituted BODIPY
dye 4,4-difluoro-1,3-dimethyl-4-bora-3a,4a-diaza-s-indacene
crystallizes in three different crystal habits, that is, as needles
(I), leaves (II), or microcrystalline sublimed
crystals (III). All crystals share the same crystal structure
but exhibit varying solid-state fluorescence from yellow-orange to
deep red. The crystal structure mainly consists of one-dimensional
chains of J-aggregates which leads to excitonic luminescence at λ
= 600 nm. The point-dipole approximation is used to calculate the
excitonic splitting to a value of 3300 cm–1, which
is in good agreement with the experimental observations. The influence
of the macroscopic appearance on the luminescence properties is discussed
in terms of reflectivity of the surface and reabsorption within the
material. It turns out that the long-range order modulates the solid-state
luminescence due to the small Stokes shift of the dye.
Detailed dissociation mechanisms were proposed in this study for BODIPY dyes. The elemental formulae of CID product ions were unambiguously assigned using FTICR-MS and unique fragment ions were discovered for the rapid identification of methyl, ethyl, butyl, tert-butyl, and phenyl substituents of individual dyes in BODIPY synthesis mixtures by low-resolution MS.
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