Two-photon polymerization of a diacrylate using fluorene photoinitiators–sensitizers

Two-photon polymerization (TPP) of a diacrylate (monomer) using two different fluorene molecules as photoinitiators–sensitizers is reported. The fluorene molecules contain e− donating (triphenylamine) or e− withdrawing (phthalimide) edge substituents. An amine co-initiator is also used lowering the polymerization threshold. The dependence of the polymerization properties (threshold, polymerization rate, lateral and axial resolution) on the type of resin, the writing power and speed as well as on the NA of the focusing lens is studied in detail. The fluorene with triphenylamine substituent exhibits favorable properties as TPP photoinitiator–sensitizer compared to the fluorene with phtalimide one, although its two-photon absorption cross-section is smaller. Polymerization of the pure monomer or monomer-amine composite (i.e. without fluorene) is also reported.