Pressure-Induced Wide-Range Reversible Emission Shift of Triphenylamine-Substituted Anthracene via Hybridized Local and Charge Transfer (HLCT) Excited State

.4-(Anthracen-9-yl)-N, N-diphenylaniline (TPA-AN) is a typical molecule belonging to a donor-acceptor system. Here, the ordered crystal and the powder of TPA-AN are used for high-pressure Raman and fluorescence experiments, and their spectroscopic features under the shearing force of grinding and the hydrostatic pressure applied by a diamond anvil cell (DAC) are compared. The mechanochromism of TPA-AN is discussed in detail based on the analysis of its single-crystal structure and pressure-driven spectral changes. During the DAC compression process, the TPA-AN crystal shows an obvious emission band shift (from 476 to 600 nm) along with a new intramolecular charge transfer state that is separated from the hybridized local and charge transfer excited state and extremely sensitive to external force. Once the pressure is relieved, the Raman and fluorescence spectra both entirely self-recover without a secondary force. To the authors' knowledge, TPA-AN crystal is one of the largest emission shift organic mechanochromic fluorescent materials among reported publications. The reversible mechanochromic property of TPA-AN for a wide-range emission shift implies a great application potential as smart stimuli-responsive layer in the fields of sensing, organic light-emitting diode displays, and data storage.