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

Abstract

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. Both coherent or incoherent singlet fission can occur, depending on transient solvent-induced energetic proximity between the states, giving rise to complex variation of the singlet fission mechanism and timescale 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. 1

Geometries and Terahertz Motions Driving Quintet Multiexcitons and Ultimate Triplet–Triplet Dissociations via the Intramolecular Singlet Fissions

“…dynamics have widely been studied using the transient absorption spectroscopic methods together with theoretical modeling taking into account the vibronic effects in the ultrafast regimes. [9][10][11][12][13][14][15] The correlated intermolecular triplet pair 1 (TT) generated with the singlet character is known to be converted to the quintet (Q) state as 5 (TT). [16][17][18][19][20][21][22][23][24][25] These TT pairs separate into individual triplets as the T+T state.…”

Change of Quadrupole Moment upon Excitation and Symmetry Breaking in Multibranched Donor‐Acceptor Dyes

“…Over the past few years, there has been a growing interest for symmetry-breaking (SB) charge transfer processes occurring in multichromophoric systems and multipolar conjugated dyes. [1] One of them, symmetry-breaking charge separation, occurs between two identical chromophores, [2][3][4][5][6][7][8][9][10][11][12][13] and offers interesting perspectives for applications in photovoltaics and artificial photosynthesis. [14,15] Here, electronic excitation can initially be entirely localised on one of the chromophores.…”

Solvent tuning of photochemistry upon excited-state symmetry breaking

“…T he current demand for highly efficient light-harvesting and photoresponsive materials is stimulating intense efforts in the design and synthesis of photoactive molecular architectures. Engineered multichromophoric arrays are emerging as promising photonic, photovoltaic and photocatalytic materials [1][2][3] . Significant work is being invested to understand, influence, and ultimately control exciton (de)localization in synthetic materials [3][4][5][6] , conjugated polymers 7-10 and natural light-harvesting complexes [11][12][13] .…”