Deep-blue solid-state emission from Ternaphthalene: Photophysical tuning via multi-chromophore architectures

We report the synthesis and photophysical characterization of a series of “all-naphthalene” multi-chromophore systems, ternaphthalenes (TNps), designed for efficient deep-blue solid-state emission. Unlike planar polycyclic aromatic hydrocarbons that suffer from aggregation-caused quenching (ACQ), the twisted molecular architecture of TNps effectively inhibits π-π stacking interactions. Consequently, several TNps exhibit crystallization-induced emission enhancement (CIEE) or retain high quantum yields (up to 0.94) in the solid state. Kinetic analysis revealed that this efficiency stems from the significant suppression of non-radiative rates (knr) due to the restricted intramolecular rotation in the rigid crystal lattice. Furthermore, a decisive topological effect on the radiative rate (kf) was demonstrated. The 1,4-, 1,5- and 2,6-linked isomers display allowed transitions with large oscillator strengths (f) and fast radiative rate (kf = ca. 5 × 108 s−1), whereas the 2,7-linked isomers exhibit forbidden-like character with prolonged lifetimes. A distinct linear correlation between the experimental and calculated values empirically supports the applicability of the Strickler-Berg relationship in both solution and solid states. These findings demonstrate that controlling the chromophore connectivity is a powerful strategy to tune excited-state dynamics for developing high-performance deep-blue organic emitters.