Zhou Qi, Wirtz Brendan M, Schloemer Tracy H, Burroughs Michael C, Hu Manchen, Narayanan Pournima, Lyu Junrui, Gallegos Arynn O, Layton Colette, Mai Danielle J, Congreve Daniel N
Department of Electrical Engineering, Stanford University, Stanford, 94305, CA, USA.
Department of Chemical Engineering, Stanford University, Stanford, 94305, CA, USA.
Adv Mater. 2023 Nov;35(46):e2301563. doi: 10.1002/adma.202301563. Epub 2023 Oct 15.
UV light can trigger a plethora of useful photochemical reactions for diverse applications, including photocatalysis, photopolymerization, and drug delivery. These applications typically require penetration of high-energy photons deep into materials, yet delivering these photons beyond the surface is extremely challenging due to absorption and scattering effects. Triplet-triplet annihilation upconversion (TTA-UC) shows great promise to circumvent this issue by generating high-energy photons from incident lower-energy photons. However, molecules that facilitate TTA-UC usually have poor water solubility, limiting their deployment in aqueous environments. To address this challenge, a nanoencapsulation method is leveraged to fabricate water-compatible UC micelles, enabling on-demand UV photon generation deep into materials. Two iridium-based complexes are presented for use as TTA-UC sensitizers with increased solubilities that facilitate the formation of highly emissive UV-upconverting micelles. Furthermore, this encapsulation method is shown to be generalizable to nineteen UV-emitting UC systems, accessing a range of upconverted UV emission profiles with wavelengths as low as 350 nm. As a proof-of-principle demonstration of precision photochemistry at depth, UV-emitting UC micelles are used to photolyze a fluorophore at a focal point nearly a centimeter beyond the surface, revealing opportunities for spatially controlled manipulation deep into UV-responsive materials.
紫外线可以引发大量适用于多种应用的光化学反应，包括光催化、光聚合和药物递送。这些应用通常需要高能光子深入穿透材料，但由于吸收和散射效应，将这些光子传递到材料表面之外极具挑战性。三重态-三重态湮灭上转换（TTA-UC）通过从入射的低能光子产生高能光子，有望解决这一问题。然而，促进TTA-UC的分子通常水溶性较差，限制了它们在水性环境中的应用。为应对这一挑战，利用一种纳米封装方法制备了与水相容的上转换胶束，能够在材料内部按需产生紫外线光子。提出了两种基于铱的配合物用作TTA-UC敏化剂，其溶解度增加，有助于形成高发射性的紫外上转换胶束。此外，这种封装方法被证明可推广到19种发射紫外线的上转换体系，获得一系列波长低至350 nm的上转换紫外发射谱。作为深度精确光化学原理验证演示，发射紫外线的上转换胶束用于在表面以下近一厘米处的焦点处光解一种荧光团，揭示了对紫外线响应材料进行空间控制操作的机会。
