Emergent Supermonomer Directs Spatially Separated Triplet Pair Generation in Dynamic Oligomers

Area of Science:

• Photochemistry
• Materials Science
• Computational Chemistry

Background:

• Efficient singlet fission (SF) requires spatially separated triplet pairs ¹(T···T) to minimize recombination losses from coupled ¹(TT) intermediates.
• The mechanism for directly generating ¹(T···T) in flexible molecules is not well understood.

Purpose of the Study:

• To elucidate the microscopic mechanism of direct ¹(T···T) generation in flexible oligomers.
• To investigate the role of polar solvents in facilitating singlet fission.

Main Methods:

• Ab initio molecular dynamics simulations on tetracene (Tc) trimers.
• Analysis of electronic coupling and energy transfer pathways.
• Spectroscopic techniques including Davydov splitting and transient spectral broadening.

Main Results:

• Polar solvents dynamically assemble chromophores into transient "supermonomers", acting as structural directors.
• The supermonomer transforms the trimer into a quasi-heterodimer, enabling a pseudo-short-range charge transfer (CT) gateway.
• This pathway facilitates the formation of a singlet-born hybrid triplet-pair precursor, leading to the desired ¹(T···T) state.
• Solvent-dependent spectral broadening confirms the supermonomer population.

Conclusions:

• Dynamic solvent-induced structural assembly is a crucial principle for designing efficient singlet fission materials.
• Supermonomers provide a novel, electronically favorable pathway for triplet-pair generation, overcoming limitations of static models.