Acceleration of a ground-state reaction by selective femtosecond-infrared-laser-pulse excitation

Abstract

Infrared (IR) excitation of vibrations that participate in the reaction coordinate of an otherwise thermally driven chemical reaction are believed to lead to its acceleration. Attempts at the practical realization of this concept have been hampered so far by competing processes leading to sample heating. Here we demonstrate, using femtosecond IR-pump IR-probe experiments, the acceleration of urethane and polyurethane formation due to vibrational excitation of the reactants for 1:1 mixtures of phenylisocyanate and cyclohexanol, and toluene-2,4-diisocyanate and 2,2,2-trichloroethane-1,1-diol, respectively. We measured reaction rate changes upon selective vibrational excitation with negligible heating of the sample and observed an increase of the reaction rate up to 24%. The observation is rationalized using reactant and transition-state structures obtained from quantum chemical calculations. We subsequently used IR-driven reaction acceleration to write a polyurethane square on sample windows using a femtosecond IR pulse.

Solvent tuning of photochemistry upon excited-state symmetry breaking

“…It also explains the lack of success in the elaboration of symmetric molecular systems that could exhibit double excitedstate proton transfer [69][70][71] . Solvent-driven SB leads to a concentration of the excitation on a particular area of a symmetric molecule and results in a strong enhancement of its photochemical reactivity providing effective means of guiding the latter in addition to mode-selective IR excitation [72][73][74][75] . Without symmetry breaking, photochemistry is significantly less efficient, if operative at all, because the excitation density, being evenly distributed over the molecule, is not sufficient to drive a chemical reaction.…”

Infrared‐Assisted Synthesis of Prebiotic Glycine

“…Stensitzki et al. have shown that femtosecond IR pulse can trigger some ground‐state reaction in solution . Recently, vibrational strong coupling was found to impact ground‐state reactivity…”

Generation and characterization of tailored MIR waveforms for steering molecular dynamics

“…However, most chemical reactions of importance to nature and technological applications do not depend on photo excitation. Instead thermal energy and activation barriers govern reaction rates [7]. Ultrashort deliberately shaped mid-infrared (MIR) laser pulses are well-suited for a systematic investigation of these reactions, because they provide three key properties [6,8] their interaction takes place on the immanent time scales of molecular dynamics.…”