Intersystem crossing processes in nonplanar aromatic heterocyclic molecules.

Area of Science:

• Photophysical properties
• Organic chemistry
• Quantum chemistry

Background:

• Monoaza[5]helicenes are a class of organic molecules with unique helical structures.
• Understanding their photophysical properties is crucial for potential applications in materials science and optoelectronics.
• Spin-orbit coupling plays a key role in photophysical processes like intersystem crossing.

Purpose of the Study:

• To investigate the photophysical properties of monoaza[5]helicenes.
• To determine how the nitrogen atom's position affects spin-orbit coupling and related processes.
• To establish a correlation between molecular geometry and spin-orbit coupling magnitude.

Main Methods:

• Joint optical spectroscopy and quantum chemistry investigations.
• Absorption and CW/time-resolved luminescence measurements.
• Density functional theory (DFT) and semiempirical quantum-chemical calculations.

Main Results:

• Photophysical properties, including intersystem crossing rates and phosphorescence lifetimes, strongly depend on nitrogen position.
• Spin-orbit coupling magnitude is directly correlated with the deviation from planarity.
• Calculated photophysical quantities align with experimental observations.

Conclusions:

• The nitrogen atom's position is a critical determinant of photophysical behavior in monoaza[5]helicenes.
• Molecular geometry, specifically deviation from planarity, influences spin-orbit coupling.
• The study provides a consistent theoretical and experimental framework for understanding these systems.