Site-Specific Photodecomposition in Conjugated Energetic Materials

Area of Science:

• Computational chemistry
• Materials science
• Photochemistry

Background:

• Energetic materials, specifically fused tetrazole and tetrazine derivatives, are being synthesized with oxygen functionalization.
• Oxygen functionalization enhances two-photon absorption and oxygen balance in these materials.
• Understanding photodecomposition mechanisms is key for controlled optical initiation of materials with nonlinear absorption properties.

Purpose of the Study:

• To investigate the photodecomposition mechanisms of bicyclic conjugated energetic materials (CEMs) with varying oxygen substitutions using nonadiabatic excited-state molecular dynamics (NEXMD).
• To model the nonradiative relaxation and bond dissociation following photoexcitation by a simulated laser pulse.

Main Methods:

• Nonadiabatic excited-state molecular dynamics (NEXMD) simulations were employed.
• Simulated Nd:YAG laser pulses were used for photoexcitation.
• Analysis of bond orders within NEXMD trajectories was utilized to identify photochemical reactions.

Main Results:

• Excess electronic energy rapidly converts to vibrational energy within 100 femtoseconds, leading to bond dissociation.
• The bicyclic framework in tetrazine derivatives enhances photochemical quantum yield.
• Increased atomic oxygen content prolongs relaxation lifetime and introduces new photodissociation pathways at oxygen-substituted sites.

Conclusions:

• NEXMD simulations provide valuable insights into the photodecomposition of oxygen-substituted CEMs.
• Bicyclic structure and oxygen content are critical factors governing photodecomposition pathways and efficiency.
• The bond order analysis method is effective for characterizing photochemical reactions in molecular dynamics simulations.