The Acetylene Bridge in Intramolecular Singlet Fission: A Boon or A Nuisance?

Various analogues of the alkylsilylacetylene group are frequently used as auxiliary groups to enhance the solubility and stability of the acene dimer core, widely used as platforms to investigate intramolecular singlet fission (iSF) mechanisms. However, while in the 2,2'-linked dimers they are primarily auxiliary groups, these are essential fragments of the bridging units in 6,6'/5,5'-linked dimers, the two preferred choices for dimerization. The starkly different iSF dynamics observed in the two variants raise the question of what role the acetylene bridges play.

Coherent photoexcitation of entangled triplet pair states.

The functional properties of organic semiconductors are defined by the interplay between optically bright and dark states. Organic devices require rapid conversion between these bright and dark manifolds for maximum efficiency, and one way to achieve this is through multiexciton generation (S→TT). The dark state TT is typically generated from bright S after optical excitation; however, the mechanistic details are hotly debated.

Controlling Intramolecular Singlet Fission Dynamics via Torsional Modulation of Through-Bond versus Through-Space Couplings.

Covalent dimers, particularly pentacenes, are the dominant platform for developing a mechanistic understanding of intramolecular singlet fission (iSF). Numerous studies have demonstrated that a photoexcited singlet state in these structures can rapidly and efficiently undergo exciton multiplication to form a correlated pair of triplets within a single molecule, with potential applications from photovoltaics to quantum information science. One of the most significant barriers limiting such dimers is the fast recombination of the triplet pair, which prevents spatial separation and the formation of long-lived triplet states.

Parallel triplet formation pathways in a singlet fission material.

Harvesting long-lived free triplets in high yields by utilizing organic singlet fission materials can be the cornerstone for increasing photovoltaic efficiencies potentially. However, except for polyacenes, which are the most studied systems in the singlet fission field, spin-entangled correlated triplet pairs and free triplets born through singlet fission are relatively poorly characterized. By utilizing transient absorption and photoluminescence spectroscopy in supramolecular aggregate thin films consisting of Hamilton-receptor-substituted diketopyrrolopyrrole derivatives, we show that photoexcitation gives rise to the formation of spin-0 correlated triplet pair (TT) from the lower Frenkel exciton state.

Synthesis and Emergent Photophysical Properties of Diketopyrrolopyrrole-Based Supramolecular Self-Assembly.

Diketopyrrolopyrrole (DPP)-based molecular semiconductors exhibit intriguing optical and charge transport properties. Herein, we rationally design a series of electronically identical but structurally distinct Hamilton receptor (HR)-based supramolecular assembly of DPP. The HR endows supramolecular assemblies via hydrogen bonding with enhanced structural ordering and excitonic couplings.