Color-Tunable Triplet–Triplet Annihilation Upconversion under Single Wavelength Excitation via Solvatochromic Annihilators

We present the rational design of a novel class of solvatochromic annihilators featuring an anthracene core functionalized with bis(triphenylamine) phenylethynyl groups. Notably, simple modulation of the push–pull character of the triphenylamine substituents enables substantial tuning of the emission wavelength while preserving nearly constant triplet energy levels. Femtosecond transient absorption spectroscopy further revealed the substituent-driven switching between localized excited (LE) and charge-transfer (CT) states during excited-state dynamics. Specifically, methoxy substitution accelerates the charge-transfer rate by 3 orders of magnitude compared to aldehyde-functionalized analogues, demonstrating precise control over CT-state population through rational substituent modification. When combined with a far-red-absorbing photosensitizer, the triplet–triplet annihilation upconversion displays solvent-polarity-responsive upconverted emission color upon 721 nm excitation, with an emission wavelength shift exceeding 80 nm. This work advances the development of stimulus-responsive, color-tunable triplet–triplet annihilation upconversion and establishes a robust foundation for designing intelligent photon upconversion materials.