Synthesis and Characterization of 1,10-Phenanthroline-mono-N-oxides

N-oxides of N-heteroaromatic compounds find widespread applications in various fields of chemistry. Although the strictly planar aromatic structure of 1,10-phenanthroline (phen) is expected to induce unique features of the corresponding N-oxides, so far the potential of these compounds has not been explored. In fact, appropriate procedure has not been reported for synthesizing these derivatives of phen. Now, we provide a straightforward method for the synthesis of a series of mono-N-oxides of 1,10-phenanthrolines. The parent compounds were oxidized by a green oxidant, peroxomonosulfate ion in acidic aqueous solution. The products were obtained in high quality and at good to excellent yields. A systematic study reveals a clear-cut correlation between the basicity of the compounds and the electronic effects of the substituents on the aromatic ring. The UV spectra of these compounds were predicted by DFT calculations at the TD-DFT/TPSSh/def2-TZVP level of theory.

Radical-Triggered Chemiluminescence of Phenanthroline Derivatives: An Insight into Radical-Aromatic Interaction

The hitherto unknown influence of 1,10-phenonthroline (1,10-phen) and its derivatives on the weak chemiluminescence (CL) of periodate-peroxide has been investigated, and a novel method for CL catalysis is described. Herein, we have deconvoluted the variation in CL intensity arising from the addition of various derivatives of 1,10-phen. Interestingly, similar derivatives of 1,10-phen show interesting differences in their reactivity toward CL. Electron-withdrawing substituents on 1,10-phen boosted the CL signals, indicating a negative charge buildup on 1,10-phen in the rate-determining step. The 1,10-phen derivatives having substitution at the C⁵=C⁶ position resulted in no CL signals due to the blockage of the reactive site. Mechanistic investigations are interpreted in terms of free radical (H₂O₂ reaction), followed by the oxygen atom transfer via an electrophilic attack of IO₄ ^- (IO₄ ^- reaction) on 1,10-phen resulting in dioxetane with enhanced CL emission. Additionally, the relationship between electronic structures and photophysical properties was investigated using density functional theory. Our results are expected to open up promising application of 1,10-phen as a molecular catalyst, providing a new strategy for metal-free catalytic CL enhancement reaction. We believe that this would foster in gleaning more detailed information on the nature of these reactions, thereby leading to a deeper understanding of the CL mechanism.