(174bv) Photon Upconversion for Real World Applications | AIChE

(174bv) Photon Upconversion for Real World Applications

Authors 

Congreve, D. - Presenter, Rowland Institute at Harvard
Upconversion, the process of turning two low energy photons into one high energy photon, has the potential to revolutionize a number of fields, from optogenetics and bioimaging to anti-counterfeit and displays. Significant hurdles, however, stand between its current implementation, most often in non-polar solvents in air-free vials, and applications in the real world. In this talk, we will detail our attempts to identify and solve these hurdles and show the benefits to various technologies that result when these hurdles can be overcome.

Current near-infrared-to-visible upconversion is almost universally performed with rubrene as the emissive molecule. While demonstrating reasonable efficiency, the use of rubrene brings significant drawbacks. First, it is not easy to chemically modulate, leaving a take-it-or-leave-it absorption and emission spectrum. Next, it is very unstable to air and moisture, severely curtailing real-world applications. To solve these issues, we synthesize a series of diketopyrrolopyrrole (DPP) derivatives. These materials are straightforward to synthesize, stable, and easily tunable. By adjusting the pendant groups, we show that the emissive properties can be tuned in ~20 nm steps across the orange-red portion of the spectrum. We show that these materials upconvert with efficiencies on the same order as rubrene. Further, these materials are stable to air and moisture, opening up real world applications.

Any interaction of upconversion with biological materials must be done in an aqueous environment, yet the most efficient molecules are all hydrophobic. This has been addressed via the introduction of upconversion into micelles or nano-encapsulants, yet these materials typically suffer from either low efficiency or low optical clarity, scattering the input excitation beam and limiting applications. We demonstrate a facile micellular synthesis that maintains both high optical clarity and high upconversion efficiency. By driving a high boiling point solvent into the core of the micelle, we maintain strong solvation of the materials and thus efficient upconversion. At the same time, we keep the size of the micelles low, allowing for optical clarity across 10 cm of solution. We then demonstrate that this straightforward technique works for five different upconversion systems spanning the visible regime.

Finally, we demonstrate initial efforts into turning these foundational improvements into real world applications. We show that the application of upconversion to photochemistry allows reactions to be performed using only near infrared light, opening up these reactions to in vivo applications, and discuss how this process could be used for anti-counterfeit and optogenetic applications.