Putting a New Spin on 3D Printing

Photocuring, the light-driven conversion of liquid resin into a solid, underpins many modern 3D printing technologies used in microelectronics, soft robotics, and dentistry. Most commercial systems rely on “Type I” photocatalysts, which generate polymerization-inducing radicals upon photoexcitation. Because these photocatalysts typically require ultraviolet (UV) light due to the energetic cost of directly cleaving bonds, Type I systems suffer from increased light scattering, limiting print speed and spatial resolution.

Additionally, unwanted side reactions limit their use in sensitive environments. To address these shortcomings, in collaboration with the Page group at UT Austin, we have developed a series of visible and near-infrared (NIR) absorbing photocatalysts for digital light processing 3D printing, a method where solid structures are built layer-by-layer by projecting a series of 2D images into a liquid resin. These photocatalysts function via a process known as triplet-triplet annihilation (TTA) photon upconversion. In triplet-triplet annihilation (TTA), two molecules, each in a low-energy spin-triplet state, combine their energy to produce a high-energy spin-singlet state capable of emitting blue or UV light, allowing Type I photoinitiators to be activated with low-energy green or red light. Because TTA responds non-linearly with light intensity, TTA photopolymerization provides improved control over printed feature fidelity. Recently, we have developed resins that retain their ability to upconvert when photocured, which holds potential for creating coatings for improved light detection and anticounterfeiting.