Enhancing NIR-to-visible upconversion in a rigidly coupled tetracene dimer: approaching statistical limits for triplet-triplet annihilation using intramolecular multiexciton states

• Published in: Chemical science (Cambridge) Vol. 15; no. 4; pp. 1283 - 1296
• Main Authors: Gilligan, Alexander T, Owens, Raythe, Miller, Ethan G, Pompetti, Nicholas F, Damrauer, Niels H
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 24.01.2024; The Royal Society of Chemistry
• Subjects: Channels; Chemistry; Chromophores; Dimers; Electron states; Near infrared radiation; Photons; Upconversion
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/d3sc04795d

Important applications of photon upconversion through triplet-triplet annihilation require conversion of near-IR photons to visible light. Generally, however, efficiencies in this spectral region lag behind bluer analogues. Herein we consider potential benefits from a conformationally well-defined covalent dimer annihilator TIPS-BTX in studies that systematically compare function to a related monomer model TIPS-tetracene (TIPS-Tc). TIPS-BTX exhibits weak electronic coupling between chromophores juxtaposed about a polycyclic bridge. We report an upconversion yield UC for TIPS-BTX that is more than 20× larger than TIPS-Tc under comparable conditions (0.16%). While the dimer UC is low compared to bluer champion systems, this yield is amongst the largest so-far reported for a tetracenic dimer system and is achieved under unoptimized conditions suggesting a significantly higher ceiling. Further investigation shows the UC enhancement for the dimer is due exclusively to the TTA process with an effective yield more that 30× larger for TIPS-BTX compared to TIPS-Tc. The TTA enhancement for TIPS-BTX relative to TIPS-Tc is indicative of participation by intramolecular multiexciton states with evidence presented in spin statistical arguments that the 5 TT is involved in productive channels. For TIPS-BTX we report a spin-statistical factor f = 0.42 that matches or exceeds values found in champion annihilator systems such as DPA. At the same time, the poor relative efficiency of TIPS-Tc suggests involvement of non-productive bimolecular channels and excimeric states are suspected. Broadly these studies indicate that funneling of photogenerated electronic states into productive pathways, and avoiding parasitic ones, remains central to the development of champion upconversion systems. We report upconversion for a rigid tetracene dimer that yields 20× that of a monomer model. This is due to a 30× relative enhancement in TTA, indicating participation by intramolecular multiexciton states, including the 5 TT, in productive channels.