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Effects of C3 ‐aromatic heterocycles on 1,3,5‐triaryl‐2‐pyrazoline sulfonium salt photoacid generators as light‐emitting diode‐sensitive cationic photoinitiators
Author(s) -
Chen Shixiong,
Zhao Xiaotian,
Jin Ming,
Huang Wanqiu,
Ye Guodong,
Pan Haiyan,
Wan Decheng
Publication year - 2021
Publication title -
journal of polymer science
Language(s) - English
Resource type - Journals
eISSN - 2642-4169
pISSN - 2642-4150
DOI - 10.1002/pol.20210333
Subject(s) - sulfonium , chemistry , photochemistry , pyrazoline , cationic polymerization , medicinal chemistry , polymer chemistry , salt (chemistry)
Four 1,5‐diphenyl‐3‐aromatic heterocyclyl ‐ 2‐pyrazoline‐based sulfonium salt photoacid generators (PAGs) with different aromatic heterocycles substituted on C3 atom and dimethyl sulfonium group on C5 atom were synthesized. These PAGs were highly photosensitive in the 365–425 nm light‐emitting diode region, and the intramolecular charge transfer from the pyrazoline ring to sulfonium salts induced efficient photolysis and high Φ H + . The heterocycles as well as their substituted positions significantly influenced the energy of the S 2 orbital, which was determined by the electrochemical and absorption properties of the PAGs. The raising of the S 2 orbital energy enlarged the energy gap of S 0 –S 2 and S 1 –S 2 , resulting in blue shift of the absorption spectra and increase in the quantum yield of photoacid generation (Φ H + ), respectively. When the energy of excited electrons was higher than that of the S 2 orbital, the transition from S 0 to S 2 (π–π*) occurred before the C‐S cleavage on S 1 and the PAGs showed high Φ H + values (0.52–0.72). The transition from S 0 to S 1 (π–σ*) occurred when the energy of electrons is lower than that of the S 2 orbital, and the PAGs showed low Φ H + value. The photopolymerization kinetics demonstrated that these PAGs were highly efficient cationic photoinitiators.