Photochemistry and Thermal Chemistry in Polymeric Ceramic Precursors

While pyrolysis of polymeric precursors has gained attention for the additive manufacturing of ceramics, the high-temperature process is energy-inefficient and time-consuming. Recently, photochemistry has been suggested to reduce energy consumption and reaction time, but the microscopic mechanisms of such accelerated reactions remain elusive. Here, we reveal distinct photochemical and thermal reaction pathways at the initial stage of silicon-carbide ceramic formation from an acylsilane precursor, using a multiscale simulation approach that combines first-principles nonadiabatic and adiabatic quantum molecular dynamics simulations with semiempirical reactive molecular dynamics simulations. While photoexcitation causes scission of Si-C bonds within 100 fs driven by the localization of a photoexcited hole, the precursor remains stable at high temperatures up to 1800 K without photoexcitation. On longer time scales, we find thermal reaction pathways involving concerted motions of many atoms, including the formation of SiCO clusters, mainly resulting from oxygen of carbonyl carbon shifting and bonding with silicon. This microscopic understanding suggests synergistic use of photochemical and thermal pathways to design ultralow-energy and facile additive manufacturing of ceramics toward achieving a sustainable society.