A pOH Jump Driven by N═N Out-of-Plane Motion in the Photoisomerization of Water-Solvated Triazabutadiene

Abstract

Utilization of photoinitiated isomerization reaction has recently emerged as a very promising platform to modulate the basicity of compounds; however, theoretical insight into its regulatory mechanism remains largely unknown and needs to be addressed. For the first time, an unexpected trans-cis photoisomerization via the N═N out of plane (NOOP) motion triggered by an in-plane inversion of N-N═N moiety was computationally demonstrated to regulate the pOH jump of water-solvated triazabutadiene by using the multiconfigurational perturbation theory together with the calculation of rate constants of protonation-deprotonation reactions. Kinetic analyses show that the dramatic pOH change can be attributed to the reinforced intramolecular hydrogen bonding resulting from water cluster reorientation and the enhanced coupling between the rotated π orbital and N lone pair of triazabutadiene in the remarkable trans-cis photoisomerization.

Protein Modification via Mild Photochemical Isomerization of Triazenes to Release Aryl Diazonium Ions

“…21,22 Importantly, previous work by our lab and others has shown that similar TBDs scaffolds undergo isomerization about the NN bond in the presence of 365 nm UV light and these isomerized compounds are more basic. 13,23,24 This increased basicity allows for protonation and release of their diazonium cargo in neutral or basic solutions. According to previous reports, 1-phenyl diazenyl piperidine analogues and similar 1-aryl-3,3-dialkyl triazenes also undergo isomerization upon irradiation with similar wavelengths of UV to their TBD counterparts, but these studies did not speak to their basicity.…”

“…We hypothesize that isomerization of the N1− N2 bond renders the triazene more basic. 23 Although the pH effects of UV isomerization have not been formally evaluated for triazenes of this type, the isomerization and subsequent increase in basicity of the molecule would enable diazonium ion release (Figure 2A). To test this mechanistic possibility, we examined pH changes within triazene solutions upon irradiation.…”

“…Having noted that these triazenes could release aryl diazonium ions at near physiological pH, we postulated that we could employ photochemistry to render them reactive in more alkaline environments. In recent years photochemistry has become increasingly popular within bioconjugate strategies and protocols allowing for accelerated reaction rates and controlled accessibility to highly reactive intermediates in situ . , Importantly, previous work by our lab and others has shown that similar TBDs scaffolds undergo isomerization about the NN bond in the presence of 365 nm UV light and these isomerized compounds are more basic. ,, This increased basicity allows for protonation and release of their diazonium cargo in neutral or basic solutions. According to previous reports, 1-phenyl diazenyl piperidine analogues and similar 1-aryl-3,3-dialkyl triazenes also undergo isomerization upon irradiation with similar wavelengths of UV to their TBD counterparts, but these studies did not speak to their basicity. , Other triazenes have been used for various UV-related applications including photoresists and UV sensitive polymers where the triazenes are ablated by high energy light to form benzene radicals. , Because we wanted to avoid radical formation, we hypothesized that using mild irradiation, we could isomerize the triazenes to render them more basic and release aryl diazonium ions, while avoiding the homolytic cleavage pathway.…”

“…The protonation mechanism is consistent with our synthetic data (Figure ). We hypothesize that isomerization of the N1–N2 bond renders the triazene more basic . Although the pH effects of UV isomerization have not been formally evaluated for triazenes of this type, the isomerization and subsequent increase in basicity of the molecule would enable diazonium ion release (Figure A).…”