Abstract
AbstractHerein, we present a new class of singlet fission (SF) materials based on diradicaloids of carbene scaffolds, namely cyclic (alkyl)(amino)carbenes (CAACs). Our modular approach allows the tuning of two key SF criteria: the steric factor and the diradical character. In turn, we modified the energy landscapes of excited states in a systematic manner to accommodate the needs for SF. We report the first example of intermolecular SF in solution by dimer self‐assembly at cryogenic temperatures.
Highlights
Singlet fission (SF) is a photophysical deactivation process, in which a singlet excited state transforms into two separated triplet exited states, involving a correlated triplet pair state 1(T1T1) with singlet multiplicity.[1,2] Overall, this process, which is based on the conservation of spin angular momentum, takes place on the picosecond or even subpicosecond timescales
Abstract: we present a new class of singlet fission (SF) materials based on diradicaloids of carbene scaffolds, namely cyclic(amino)carbenes (CAACs)
The absorption maxima of the three diradicaloids redshift significantly with increasing length of the linker. We attribute this to the decreasing energy difference between the highest occupied natural orbital (HONO) and lowest unoccupied natural orbital (LUNO), leading to a sizeable diradical character
Summary
Linking two separate SF chromophores, such as, for example, tetracenes and pentacenes, by molecular bridges has transformed into a viable strategy to study the nature of 1(T1T1) and (T1 + T1) even in solution.[37,38,39,40] A number of drawbacks go, hand-in-hand with the covalent linkages. Implicit is an internal conversion from a singly excited, bright state into a doubly excited, dark state of Ag symmetry and/or lower energy en-route towards a correlated 1(T1T1) with strong inter-triplet binding energies.[41,42,43,44] SF materials that feature doubly excited, singlet states, namely class III chromophores, are rare; most prominent examples are oligoenes and polyenes, in general, and carotenoids, in particular.[14,45,46] This area of SF remains essentially unexplored and previous studies were dedicated to probing films, aggregates, and monomers rather than dimers. We establish SF for materials with exceptionally large diradical character.[36,53]
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