A Straightforward Synthesis
and Structure–Activity
Relationship of Highly Efficient Initiators for Two-Photon Polymerization
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Abstract
The development of practical two-photon absorption photoinitiators
(TPA PIs) has been slow due to their complicated syntheses often reliant
on expensive catalysts. These shortcomings have been a critical obstruction
for further advances in the promising field of two-photon-induced
photopolymerization (TPIP) technology. This paper describes a series
of linear and cyclic benzylidene ketone-based two-photon initiators
containing double bonds and dialkylamino groups synthesized in one
step via classical aldol condensation reactions. Systematic investigations
of structure–activity relationships were conducted via quantum-chemical
calculations and experimental tests. These results showed that the
size of the central ring significantly affected the excited state
energetics and emission quantum yields as well as the two-photon initiation
efficiency. In the TPIP tests the 4-methylcyclohexanone-based initiator
displayed much broader ideal processing windows than its counterparts
with a central five-membered ring and previously described highly
active TPA PIs. Surprisingly, a writing speed as high as 80 mm/s was
obtained for the microfabrication of complex 3D structures employing
acrylate-based formulations. These highly active TPA PIs also exhibit
excellent thermal stability and remain inert to one-photon excitation.
Straightforward synthesis combined with high TPA initiation efficiency
makes these novel initiators promising candidates for commercialization