Designing an Efficient Singlet Fission Material with B-N Substitution in Pyrene: A Model Exact Study

Area of Science:

• Materials Science
• Quantum Chemistry
• Organic Electronics

Background:

• Intermolecular singlet fission (x-SF) is a crucial process for developing efficient organic solar cells.
• Designing materials that meet the thermodynamic energy criteria for x-SF is challenging.
• Pyrene derivatives are explored for x-SF, but pristine pyrene is endothermic.

Purpose of the Study:

• To investigate the electronic structure of boron (B)-nitrogen (N)-substituted pyrene molecules.
• To assess the potential of these substituted pyrenes as efficient intermolecular singlet fission (x-SF) materials.
• To determine if B-N substitution can optimize the energy landscape for x-SF.

Main Methods:

• Computed low-lying excited states of BN-embedded pyrene molecules using the Pariser-Parr-Pople (PPP) model Hamiltonian.
• Employed exact diagonalization of the PPP model Hamiltonian.
• Compared computational results with Time-Dependent Density-Functional Theory (TDDFT) and Equation of Motion Coupled-Cluster Singles and Doubles (EOM-CCSD) values.

Main Results:

• Boron-nitrogen substitution in pyrene was found to increase the lowest singlet-triplet energy gap, aiding x-SF.
• Exact diagonalization of the PPP model Hamiltonian indicated that certain (BN)2 substitutions make pyrene isoergic for x-SF.
• Calculated low-lying excited state energies closely matched experimental values, outperforming EOM-CCSD and TDDFT.
• Low spin-orbit coupling constants were computed for BN-substituted pyrene, supporting its SF material applicability.

Conclusions:

• Boron-nitrogen substitution is an effective strategy to design efficient intermolecular singlet fission (x-SF) materials based on pyrene.
• The modified pyrene derivatives show promise for optoelectronic applications due to optimized electronic structures for x-SF.
• The PPP model Hamiltonian provides accurate predictions for excited states in these systems.