Bulky side chains promote a molecular packing and intermolecular coupling that effect high-efficiency singlet fission in amorphous solids of pentacene derivatives.

Functionalization of organic semiconductors through the attachment of bulky side groups to the conjugated core has imparted solution processability to this class of otherwise insoluble materials. A consequence of this functionalization is that the bulky side groups impact the solid-state packing of these materials. To examine the importance of side-group electronic character on accessing the structural phase space of functionalized materials, germanium was substituted for silicon in triisopropyl­silylethynyl­pentacene (TIPS-Pn) to produce triisopropyl­germanyl­ethynyl­pentacene (TIPGe-Pn), with the TIPGe side group comparable in size to TIPS, but higher in electron density. We find TIPGe-Pn single crystals exhibit slip-stack, herringbone, and brickwork packing motifs depending on growth conditions, a stark contrast to TIPS-Pn, which accesses only the brickwork packing motif in both single crystals and thin films. Polycrystalline thin films of TIPGe-Pn exhibit two new, unidentified polymorphs from spin-coating and postdeposition annealing. Our experiments suggest that access to the structural phase space is not guided solely by the size of the side group; the electronic character of the side group in functionalized compounds also plays a significant role. As such, simple atomistic substitutions can cause significant differences in the accessible solid structures.

The generation and transfer of triplet excitons across the molecular-semiconductor interface represents an important technological breakthrough featuring numerous fundamental scientific questions. This contribution demonstrates curious delayed formation of TIPS-pentacene molecular triplet excitons bound on the surface of PbS nanocrystals mediated through the initial production of a proposed charge transfer intermediate following selective excitation of the PbS quantum dots. Ultrafast UV-vis and near-IR transient absorption spectroscopy was used to track the dynamics of the initial PbS exciton quenching as well as time scale of the formation of molecular triplet excited states that persisted for 10 μs on the PbS surface, enabling subsequent energy and electron transfer reactivity. These results provide the pivotal proof-of-concept that PbS nanocrystals absorbing near-IR radiation can ultimately generate molecular triplets on their surfaces through processes distinct from direct Dexter triplet energy transfer. More broadly, this work establishes that small metal chalcogenide semiconductor nanocrystals interfaced with molecular chromophores exhibit behavior reminiscent of supramolecular chemical systems, a potentially impactful concept for nanoscience.

Herein, we describe the design and synthesis of a suite of molecules based on a benzodithiophene "universal crystal engineering core". After computationally screening derivatives, a trialkylsilylethynebased crystal engineering strategy was employed to tailor the crystal packing for use as the active material in an organic field-effect transistor. Electronic structure calculations were undertaken to reveal derivatives that exhibit exceptional potential for high-efficiency hole transport. The promising theoretical properties are reflected in the preliminary device results, with the computationally optimized material showing simple solution processing, enhanced stability, and a maximum hole mobility of 1.6 cm 2 V À1 s À1 .