Physics

Organic chemistry

Anthracene

Stereochemistry

Organic semiconductor

Fission

Semiconductor

Singlet fission

Excited state

Atomic physics

Neutron

Chemical physics

Exciton

Nuclear physics

Chemistry

Condensed matter physics

Tetracene

Singlet state

Molecular physics

Intramolecular force

Optoelectronics

Photochemistry

Journal of the American Chemical Society

Singlet fission in organic semiconductors causes a singlet exciton to decay into a pair of triplet excitons and holds potential for increasing the efficiency of photovoltaic devices. In this combined experimental and theoretical study, we reveal that a covalent dimer of the organic semiconductor tetracene undergoes activated singlet fission by qualitatively different mechanisms depending on the solvent environment. We show that intramolecular vibrations are an integral part of this mechanism, giving rise to mixing between charge transfer and triplet pair excitations. Either coherent or incoherent singlet fission can occur, depending on the transient solvent-induced energetic proximity between the states, giving rise to complex variation of the singlet fission mechanism and time scale in the different environments. Our results suggest a more general principle for controlling the efficiency of photochemical reactions by utilizing transient interactions to tune the energetics of reactant and product states and switch between incoherent and coherent dynamics.

Switching between Coherent and Incoherent Singlet Fission via Solvent-Induced Symmetry Breaking