Emergent Supermonomer Directs Spatially Separated Triplet Pair Generation in Dynamic Oligomers

The spatially separated triplet pair ¹(T···T) is critical for efficient singlet fission (SF) to overcome the recombination losses associated with the strongly coupled ¹(TT) intermediate. However, the microscopic mechanism governing its direct generation in flexible oligomers remains elusive. Here, using ab initio molecular dynamics simulations on tetracene (Tc) trimers, we discover that polar solvents act as "structural directors" that dynamically assemble adjacent chromophores into a transient "supermonomer", a pre-assembled partially delocalized electronic subunit that is inaccessible in static models. This supermonomer transforms the trimer into a functional supermonomer-monomer quasi-heterodimer. Coupling and energetic analyses reveal that the terminal long-range charge transfer (LRCT) gateway in the monomer-localized framework is electronically inefficient, whereas the supermonomer opens a strongly allowed pseudo-short-range CT gateway while maintaining favorable SF energetics. This topology enables formation of a singlet-born hybrid triplet-pair precursor ¹(TT) state in which one triplet is delocalized across the supermonomer (T₁). Driven by thermodynamic gradients, the supermonomer T subsequently localizes onto a terminal unit, yielding the ¹(T···T) state. Calculated Davydov splitting and experimental solvent-dependent transient spectral broadening provide spectroscopic fingerprints of the supermonomer population. These findings establish dynamic solvent-induced structural assembly as a key design principle for next-generation SF materials.