Indications for a Direct Singlet Fission Mechanism in TIPS-Pentacene Crystals from Hybrid DFT/MRCI and Molecular Mechanics Studies
Year: 2025
Type: article
Abstract: A hybrid quantum mechanics/molecular mechanics setup was used to model the singlet fission (SF) of electronically excited 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) in the crystalline phase. The optically bright S^bright_1 state possesses nearly identical excitation energies and oscillator strengths in the two nonequivalent dimer units with large and small structural overlap, respectively. A shearing/tilting motion of the two slip-stacked TIPS-pentacene building blocks is the key for stabilizing the singlet-coupled triplet-pair state, ^1(TT), in the large/small overlap situation. In both dimer models, the S^bright_1 and ^1(TT) states swap energetic order upon geometry relaxation, indicative of strong nonadiabatic coupling between these states and a direct SF mechanism in TIPS-pentacene crystals, at variance with unsubstituted pentacene. The overall energy balance E(S^bright_1 ) -(E(T_1)+E(T_1)) remains positive at all investigated nuclear arrangements. Charge-transfer states and the ferromagnetically coupled ^5(TT) state lie energetically too high for taking part in the SF mechanism.
Authors: Timo Schulz, Simon Hédé, Christel M. Marian
Institution: Heinrich Heine University Düsseldorf
Language: English
Subfield: Electrical and Electronic Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: green
Funder: Deutsche Forschungsgemeinschaft
OpenAlex ID: W4408337005