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 ([Me 2 pi][HSO 4 ] 2 ) ionic liquid (IL) catalyst (3 mol%). Mechanistic studies are performed with DFT M06 L functional. The utilized IL catalyst holds two moles of HSO 4 − 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(sp 3 )‐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.