Piezochromic luminescence of amide and ester derivatives of tetraphenylpyrene-role of amide hydrogen bonds in sensitive piezochromic response

A series of amide and ester derivatives of 1,3,6,8-tetraphenylpyrene (TPPy) were prepared, and their solid-state luminescence, molecular packing, and piezochromic responses were studied in order to improve and refine the design concept of piezochromic luminescent materials based on the use of multiple hydrogen bonds and close packing of disk-shaped aromatic cores as competing factors in the control of molecular packing. The amide derivative of TPPy having hexyl side chains (1b) showed a sensitive luminescence response at a relatively low applied pressure, which was ascribed to the hydrogen bond-directed H-type columnar packing. Application of higher pressure induced considerable destruction of the hydrogen bond-directed structure, leading to the state where close packing was the overriding factor directing the molecular assembly and showed similar piezochromic response to that of the ester derivative. Based on the results, the role of the amide hydrogen bonds and the side chains was discussed in detail.