Structure and properties of N-heterocycle-containing benzotriazoles as UV absorbers

• Two novel N-heterocycle-bearing UVAs were synthesized.
• The excellent absorption comes from S0 → S1 electronic transition band of the Enol forms.
• CBHDCP and CBMPP show much higher εmax than commercial UVA Tinuvin 326.

Two N-heterocycle-containing benzotriazole compounds (CBHDCP, CBMPP) were synthesized and their structures were confirmed by FT-IR, 1H NMR, mass spectroscopy and elemental analysis. Their spectral properties compared with that of a common commercial benzotriazole UV absorber Tinuvin 326 in solvents were measured and analyzed using molecular orbital calculations. It was found that the experimentally obtained optical properties were in close agreement with the theoretically obtained results. Besides, CBMPP is much superior to CBHDCP acting as an effective UV absorber on polyethylene terephthalate fabric due to its combinative higher exhaustion and higher molar extinction coefficient. The exhaustion difference on polyethylene terephthalate fabric among N-heterocycle-containing benzotriazoles (CBHDCP, CBMPP) and Tinuvin 326 were then measured and explained by the solubility parameter theory. The results agreed with the rule that compounds with higher exhaustion on fiber have solubility parameter much closer to that of fiber polymer.