Probing the Evolution of Molecular Packing Underlying HJ-Aggregate Transition in Organic Semiconductors Using Solvent Vapor Annealing

Abstract

In this work, we used solvent vapor annealing as a route toward controlled cluster growth of a nitrogen-substituted terrylene molecule (7,8,15,16-tetrazaterrylene or TAT) to probe the underlying molecular packing behind the exciton band curvature (EBC) inversion leading to a so-called HJ aggregates. Using a suite of photoluminescence (PL) imaging tools, we show that the EBCas signaled by PL spectral signaturesare correlated with distinct polarization and defocused emission patterns suggestive of a high degree of chromophore alignment. Selected area electron diffraction showed that the small aggregates adopt nominally the same crystal packing structure as the extended crystals though with a different plane orientation ([010] vs [011]) with respect to the surface normal. These findings demonstrate experimentally that the EBC inversion is not due to a crystal polymorphism but, rather subtle differences in molecular registration that profoundly impacts interchromophore coupling.

A twist in the non-slanted H-mers to control π-conjugation in 2-dimensions and optical properties

“…The synthesis and study of structurally well-defined, monodisperse p-conjugated oligomers of diverse shapes that are conjugated in 2-dimensions provide insights into the impact of molecular shape on the extension of p-conjugation in 2-dimensions. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] Also, nanosized 2D-p-conjugated oligomers lend an opportunity to realize unique physical and electronic properties that are unattainable with linearly conjugated oligomers. For example, cruciform-shaped (also reported as X-mers) [3][4][5]20 optically active p-conjugated oligomers developed by the Bunz group and others exhibit spatially non-overlapping frontier molecular orbitals, which bestowed them with remarkable sensory behavior.…”

Orientation distributions of vacuum-deposited organic emitters revealed by single-molecule microscopy

“…For example, single-molecule defocused orientation and position imaging (DOPI) has been employed to map conformational changes in biomolecules, as well as the morphology of lipid membranes and glassy polymers [30][31][32][33][34] . Great strides have been made to adapt SMFM to the study of organic semiconductors, such as conjugated polymers, dendrimers, perovskite nanocrystals, and OLED emitters [35][36][37][38][39][40][41][42][43][44] . However, those studies are mostly limited to solution-processed and solution-based systems.…”