Disclosing Early Excited State Relaxation Events in Prototypical Linear Carbon Chains.

Area of Science:

• Materials Science
• Physical Chemistry
• Nanotechnology

Background:

• One-dimensional (1D) sp-hybridized carbon nanostructures, like polyynes, are predicted to have exceptional properties.
• Despite synthesis advances, their photophysics and excited-state dynamics remain poorly understood.

Purpose of the Study:

• To investigate the photophysics and excited-state relaxation processes in a prototypical polyyne, hydrogen-capped hexayne (H─(C≡C)₆─H).
• To provide a comprehensive understanding of early-time photoinduced events in sp-carbon chains for fundamental knowledge and applications.

Main Methods:

• Transient absorption experiments with high temporal resolution (<30 fs).
• Synthesis of monodispersed hydrogen-capped hexayne via laser ablation in liquid.
• Computational studies using ground state density functional theory (DFT) and time-dependent (TD)-DFT calculations.

Main Results:

• Ultrafast internal conversion from a bright singlet excited state to a low-lying dark state occurs with a 200 fs time constant.
• Subsequent thermalization on the picosecond timescale and decay of the low-energy singlet state occur over hundreds of picoseconds.
• The observed timescales are independent of the end groups capping the sp-carbon chain.

Conclusions:

• The study elucidates the primary photoinduced events in polyynes, revealing ultrafast excited-state dynamics.
• Understanding these photophysical processes is essential for advancing the fundamental knowledge of sp-carbon materials.
• These findings are critical for the development of novel optoelectronic and light-harvesting applications using low-dimensional nanostructured carbon.