Pressure Tuning Dual Fluorescence of 4-(N,N-Dimethylamino)benzonitrile

The intramolecular charge-transfer (ICT) emission band in the dual fluorescence of the 4-(N,N-dimethylamino)benzonitrile (DMABN) molecular crystal exhibits increase in response to compression up to 10 GPa. On the basis of Raman and angle dispersive X-ray diffraction (ADXRD) experiments combining with computational studies, the mechanism of this phenomenon could be assigned to the change of the intramolecular geometrical conformation, especially for the decrease of the dihedral angle between the dimethylamino (NMe2) and phenyl moieties. Meanwhile the reduction of excited-state energies and the HOMO-LUMO band gap leads to the redshifts of photoluminescence (PL) spectra and the absorption edge, respectively. Competing with the aggregation caused quenching (ACQJ effect, the planarity of molecular conformation and the slight rotation of the NMe2 group under high pressure both could enhance the ICT process, which will contribute to the revelation of the ICT mechanism and designs of new piezochromic luminescent materials.