Comparative Photoinitiating Performances of Donor-Acceptor Multibranched Triphenylamines Designed for Light-Triggered Micropatterning Applications

The present investigation describes an original structure-reactivity relationship within a series of type II photoinitiators designed on the basis of a multibranched molecular engineering strategy. Each photoinitiator indeed incorporates a triphenylamine subunit decorated with a combination of parasubstituents, implying anisole or thioanisole as pi-conjugated donor groups and multiple reactive ketones as electron-acceptor functions. Interestingly, we demonstrate that the photoinitiating efficiency of such multipolar derivatives is mainly modulated by a solvent-mediated interplay between intersystem crossing and intramolecular charge transfer processes at the excited singlet state. Such a balancing mechanism drastically regulates the population of highly reactive excited triplet species in such a manner that the photoinitiation performance of the dyes can be enhanced by more than 1 order of magnitude within the series. Taking advantage of this amplified photoreactivity, we illustrated the versatile application potential of the best-performing photoinitiating prototype, which was both employed both in a rapid two-dimensional (2D) photopatterning process through liquid crystal display (LCD) image projection and in three-dimensional (3D) micro-optics fabrication at the surface of an optical fiber.

Automated summary

This study describes an original structure-reactivity relationship within a series of type II photoinitiators based on a multibranched molecular engineering strategy. It was found that the photoinitiating efficiency of these multipolar derivatives is mainly modulated by a solvent-mediated interplay between intersystem crossing and intramolecular charge transfer processes at the excited singlet state. This balancing mechanism significantly enhances the photoinitiation performance by more than 1 order of magnitude in the series.