Solid-State TICT-Emissive Cruciform: Aggregation-Enhanced Emission, Deep-Red to Near-Infrared Piezochromism and Imaging In Vivo

Near-infrared piezochromic materials presenting fluorescence responses with clear color differences and good penetrability have important potential applications, but a few such organic compounds are developed. Twisted intramolecular charge transfer (TICT) emission is versatile in solutions, especially for preparing bio/chem-sensing materials due to the excellent sensitivity of the emission to alterations in the external environment. By analogy, the solid-state TICT-emissive chromophores are probably excellent candidates for the environmentally responsive material. Herein, X-shaped pi architectures that exhibit solid-state TICT emission are developed, and their luminescent chromism and bioimaging properties are investigated. Initially, the cruciform fluorophore exhibits anomalous aggregation-enhanced emission (AEE) and dual emission due to the existence of a TICT state. Interestingly, TICT emission is observed even in the aggregated state because the spacious environment around the bulky triphenylamine allows for rotation. During the compression process, the TICT-based fluorophore demonstrates deep-red to near-infrared piezochromic behavior with a remarkable redshift (162 nm) and high sensitivity (15.1 nm GPa(-1)). The bioimaging performance of the TICT-emissive dye suggests its potential utility as a fluorescent probe for biological applications.