Enhancing photon upconversion properties in anthracene derivatives through meticulous control of excluded volume...

Photon upconversion, which converts low-energy photons into high-energy photons, provides a strategy for overcoming the limitations imposed by excitation wavelengths in energy and biology applications. Recent advancement in triplet-triplet annihilation-based photon upconversion (TTA-UC) witnesses the importance of the bulkiness of the substituents in chromophores to avoid quenching of the singlet and triplet. One of the simplest bulky substituents, the tert-butyl (tBu) group, has been introduced into acene derivatives and shown both positive and negative effects on UC performance, underscoring the importance of further structure-property investigations. Here, we systematically synthesized anthracene derivatives of 9,10-bis(phenylethynyl)anthracene (BPEA) and 9,10-bis[(triisopropylsilyl)ethynyl]anthracene (TIPS-Ac), each bearing bulky tBu substituents. The relationship between the excluded volume imparted by these substituents and UC performance in both solution and the solid state was investigated. A moderate intermolecular distance effectively suppressed singlet and triplet quenching, yielding high UC quantum yields of approximately 15% in the solution state with both chromophores. A significant extension of the triplet lifetime was also observed in a donor-acceptor bilayer solid film, demonstrating the simple yet positive effects of tBu on the anthracene backbone, thereby boosting the UC performances in versatile material forms.