Bending-Induced Fluorescence Shift of Dual-Shaped Flexible Organic Crystals from a Diaminoterephthalate with Nonplanar Conformation

The development of flexible crystalline materials with a bending-induced fluorescence shift (BIFS) remains a challenge. The flexible crystals with BIFS properties reported so far are mainly realized by chemical structures with a planar conformation or a special donor-π-acceptor configuration. Here, BIFS is simultaneously achieved in the straight-shaped (Cry-S) and naturally curved (Cry-NC) crystal prepared by a halogenated diaminoterephthalate derivative with a nonplanar conformation. Cry-S displays an obviously reversible red-shifted fluorescence (∼20 nm) in the bent position compared with its original (undeformed) state. In contrast to the naturally curved position (undeformed), Cry-NC similarly shows a red shift (∼16 nm) at its acutely bent position (deformed). In addition, Cry-S and Cry-NC can be reversibly bent in a wide temperature range from - 6 to 180 °C under mechanical external force. It is hoped that this work would facilitate the design of BIFS materials and their applications in the field of mechanically stimulated light sensors.