Optimal Wavelengths and Solvents to Modulate Diazirine Kinetics

Abstract

Diazirine photolysis generates reactive carbene species, useful for indiscriminate cross-linking and insertion reactions with amino acids and polyolefins. However, methods to increase the carbene efficiency and limit the benign diazoalkane intermediate remain uncharted. Herein, we correlate diazirine depletion to common experimental parameters such as LED wavelength, temperature, solvent, and grafted functional groups. Broad wavelength activation impeded the formation of diazoalkane, presenting a light-based method to limit this yellow-inducing intermediate. Kinetics rate (per joule) values of diazirine depletion and diazoalkane generation served as the performance metric, permitting comparisons across all parameter variables. Photokinetics were independent of temperature from 25 to 70 °C. Highest rates were found in ester-containing solvents and ether conjugated diazirine. Overall, the novel irradiation arrangement reduces the reliance on UVA for photoactivation and increases the efficiency of diazirine as a carbene precursor.