Luminogens Based on Cyano-Substituted Anthracene Isomers: Different Molecular Packing and Distinct Piezochromic Properties

Pure organic materials with piezochromic property have been intensively studied in recent years. Many examples describe response to both mechanical grinding and hydrostatic pressure, but the examples in realizing high color contrast as well as high sensitivity, especially under high external pressure, are very rare which hampers their practical applications as pressure sensors. Herein, two anthracene-based structural isomers, NDHA-p and NDHA-m, are developed applying 9,10-bis(diphenylmethylene)-9,10-dihydroanthracene (DHA) as the basic skeleton and substituted by four cyano groups on para- or meta-positions of the periphery benzene rings, respectively. In high-pressure experiment, as compared to the NDHA-m which shows a color contrast of 60 nm and a sensitivity of 7.87 nm·GPa-1, NDHA-p exhibits a dramatically larger color contrast of 138 nm and higher sensitivity of 13.20 nm·GPa-1, whose performance is among the best pure organic piezochromic materials so far. The systematical experimental and theoretical analyses indicate that NDHA-p possesses a lower crystal density, relatively looser molecular packing mode, and higher degree of electronic communications than NDHA-m, which are responsible for the excellent piezochromic performance. This design method will open a new avenue for controlling the molecular packing configuration of luminescent materials via structural isomerization, and further extending their applications.