Enhancing photon upconversion properties in anthracene derivatives through meticulous control of excluded volume around π-systems

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.