Infrared-driven topochemical reaction of a diacetylene

Area of Science:

• Solid-state chemistry
• Vibrational spectroscopy
• Photochemistry

Background:

• Driving chemical reactions using infrared (IR) vibrational excitation in condensed phases is challenging due to rapid energy dissipation.
• Intramolecular vibrational redistribution (IVR) and solvent collisions quickly dissipate energy, hindering efficient reaction induction.

Purpose of the Study:

• To investigate if topochemical lattice preorganization can enable efficient infrared-driven chemical reactions in condensed phases.
• To understand the mechanism of enhanced reaction rates under IR excitation in preorganized systems.

Main Methods:

• Utilized 2,4-heptadecadiynoic acid (DA-17) microcrystals as a model system.
• Employed spectral deconvolution, variable-temperature X-ray diffraction, and quantum chemical calculations.
• Used selective excitation with a tunable mid-IR laser.

Main Results:

• Topochemical lattice preorganization enabled IR-driven reactions approximately 14-fold faster than thermal activation at the same temperature.
• Identified three distinct monomer populations: reactive confined layers and an inert amorphous fraction.
• Discovered that the symmetric alkyne stretch is a key reaction-coordinate-coupled mode under confinement, a selectivity lost in disordered states.

Conclusions:

• Preorganization directs vibrational energy into the reaction coordinate before dissipation, enabling efficient solid-state chemistry.
• The observed self-acceleration in IR-irradiated films suggests a mechanism beyond simple heating.
• Established a physical-organic model for designing mode-selective solid-state reactions.