Structure–Photoluminescence Correlation for Two Crystalline Polymorphs of a Thiophene–Phenylene Co-Oligomer with Bulky Terminal Substituents

Two
crystal polymorphs of a thiophene–phenylene hexamer
with bulky terminal substituents are characterized by different molecular
conformations and parallel versus herringbone packing. Irrespective
of their similar emissive spectra and common H-aggregate features,
evidenced by crystal structure analysis and confirmed by solid-phase
and excited-state first-principles calculations, their luminescence
is relatively high and, for one form, nearly double than that for
the other. Interaromatic packing energy contributions are established
by quantum chemical calculations and can be compared quantitatively
as the same species in different crystal environments is examined.
The different luminescence efficiency of the two phases highlights
the crucial role of the interaromatic packing for the luminescence
properties of polyaromatic oligomers.