Design of Phthalocyanine Metal Complexes for Efficient Far-Red to Near-IR Light-Initiated Photopolymerizations

Abstract

Efficient near-infrared (NIR) photopolymerization is promising for applications such as hydrogel bioprinting, composite manufacturing, and other technologies that benefit from deep light penetration and low-energy activation. Yet, design principles for optimizing NIR photoinitiators, particularly those based on earth-abundant or metal-free elements, remain limited. Here, a library of phthalocyanine (Pc) and naphthalocyanine (Nc) derivatives was synthesized, characterized, and evaluated as photoredox catalysts for NIR-induced radical polymerizations. Variations in metal center (Zn, Si, Pd), αsubstitution (pentyl or butoxy), and π-extension (Pc vs. Nc) enabled tuning of light absorption, excited-state energies and lifetimes, and triplet excited state quantum yields. Polymerization kinetics were quantified using real-time FTIR spectroscopy under LED irradiation (740-940 nm), with photon absorption normalized to allow direct comparison of internal quantum yields. This work provides a framework for quantitative benchmarking of NIR photoinitiators under controlled conditions. Among the catalysts studied, a Pd-Pc complex showed the highest internal efficiency, while a Si-Nc catalyst outperformed a leading commercial cyanine initiator, highlighting the potential of silicon as a sustainable alternative to precious metals.These results establish clear structure-property relationships and offer guiding principles for the design of next-generation NIR photoinitiators suited for biomedical and advanced manufacturing technologies.

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Article information

Article type
Paper
Submitted
16 Jul 2025
Accepted
11 Aug 2025
First published
12 Aug 2025
This article is Open Access
Creative Commons BY-NC license

J. Mater. Chem. A, 2025, Accepted Manuscript

Design of Phthalocyanine Metal Complexes for Efficient Far-Red to Near-IR Light-Initiated Photopolymerizations

C. J. O'Dea, L. M. Loftus, T. A. Grusenmeyer, J. Isokuortti, J. Ong, S. T. Roberts and Z. A. Page, J. Mater. Chem. A, 2025, Accepted Manuscript , DOI: 10.1039/D5TA05756F

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