# Donor–acceptor complexes between photoinitiators and hybrid organic–inorganic SZ2080™ photoresist

## TL;DR

This paper explores how photoinitiators interact with a hybrid organic-inorganic material to improve 3D nanostructure fabrication.

## Contribution

The study reveals donor–acceptor complex formation between photoinitiators and SZ2080™, enhancing photopolymerisation performance.

## Key findings

- UV/Vis spectra show ground-state absorption changes due to coordination interactions.
- 1H NMR confirms coordination of Michler's ketone and IRG369 with Zr(iv) centers in SZ2080™.
- Donor–acceptor complexes improve the fabrication window for MPP.

## Abstract

Multi-photon photopolymerisation (MPP) based on organic–inorganic resins has emerged as a promising technique for the fabrication of complex three-dimensional nano- and micro-structures. Among the prepolymers used for MPP, SZ2080™, synthesised via sol–gel method, stands out for its hybrid nature, comprised of an organic and inorganic network. This photoresist is usually photosensitised with the photoinitiators IRG369 and Michler's ketone, that are responsible for initiating polymerisation. The incorporation of these photoinitiators induces significant changes in the ground-state absorption of the material and enables a broad fabrication window. Despite its broad application, the fundamental processes governing the performance of SZ2080™ remain poorly understood. In this study, we systematically investigate the optical characteristics of SZ2080™ sensitised with IRG369 and Michler's ketone using UV/Vis absorption, steady-state fluorescence, Raman, along with Fourier-transformed infrared and nuclear magnetic resonance (NMR) spectroscopies. The UV/Vis spectra reveal pronounced alterations in ground-state absorption, suggesting coordination-related interactions. Vibrational spectroscopy further supports these findings, indicating that the observed modifications are linked to changes in the inorganic network of SZ2080™. Finally, 1H NMR confirms that the diethylamino groups of Michler's ketone, along with the carbonyl groups of IRG369, coordinate with the Zr(iv) centres in the SZ2080™ matrix. The link between spectroscopic characterisation and MPP fabrication highlights that controlled complex formation could greatly improve the fabrication window.

Michler's ketone is one representative photointiator able to form a donor–acceptor complex with SZ2080™ prepolymer, thereby enhancing the photopolymerisation performance.