Spin Mixing in Intramolecular Singlet Fission: A First-Principles-Based Quantum Dynamical Study.

Area of Science:

• Quantum chemistry
• Photophysics
• Organic electronics

Background:

• Intramolecular singlet fission (ISF) is a key process for enhancing solar cell efficiency.
• Pentacene dimers are promising materials for ISF due to their electronic properties.
• Understanding the spin dynamics of ISF is crucial for optimizing energy conversion.

Purpose of the Study:

• To investigate the spin dynamics of triplet-pair states in pentacene dimers with varying linker positions.
• To elucidate the role of spin dipole-dipole interactions in populating different spin manifolds.
• To determine how molecular geometry influences ISF dynamics.

Main Methods:

• First-principles calculations
• Density matrix quantum dynamical approach
• Theoretical modeling of spin interactions

Main Results:

• Spin dipole-dipole interactions significantly populate the quintet spin manifold when singlet, triplet, and quintet states are quasi-degenerate.
• Regioisomerism (ortho, meta, para) profoundly impacts spin-mixing dynamics.
• Molecular arrangement affects the relative populations of spin states and the timescale of the process.

Conclusions:

• The study reveals a complex interplay between spin states during ISF in pentacene dimers.
• Geometric arrangement is a critical factor controlling spin dynamics and efficiency.
• These findings provide insights for designing advanced materials for organic electronics.