Construction of New Azo-group Containing Polycyclic Imidazole Derivatives: Computational Mechanistic, Structural, and Fluorescence Studies

Three polycyclic aromatic imidazole derivatives 2-phenyl-1-(4-(phenyldiazenyl)phenyl)-1H-phenanthro[9,10-d]imidazole (PRO), 2-(4-methoxyphenyl)-1-(4-(phenyldiazenyl)phenyl)-1H-phenanthro[9,10-d]imidazole (PRO1), 2-(2,4-dichlorophenyl)-1-(4-(phenyldiazenyl)phenyl)-1H-phenanthro[9,10-d]imidazole (PRO2) are synthesized with one-pot four component fusion reaction using 1,4-dimethylpyperazinium dihydrosulfate ([Me₂pi][HSO₄]₂) ionic liquid (IL) catalyst (3 mol%). Mechanistic studies are performed with DFT M06 L functional. The utilized IL catalyst holds two moles of HSO₄ ⁻ per one mole of 1,4-dimethylpyperazinium (cation part), which increases its catalytic performance in a trans form (Figure 1). The IL catalytic effects are determined and described in the optimized transition state structures (Figure 2). Important transition states for the rate-limiting step (▵G^≠=26.56 kcal/mol), the five-membered imidazole ring formation (▵G^≠=6.9 kcal/mol), and the C(sp³)-H (▵G^≠=2.06 kcal/mol) activation are optimized. The PRO fluorescence properties are studied computationally (HOMO and LUMO energy gap=2.41 eV) and experimentally.