Aggregation induced emission enhancement of 4,4′-bis(diethylamino)benzophenone with an exceptionally large blue shift and its potential use as glucose sensor

Abstract

Optical emission from a luminogen in solid state is generally red shifted with respect to its solution phase emission. However, in our present study, we report exceptionally large blue shifted enhanced emission from aggregated hydrosol of 4,4′-bis(diethylamino)benzophenone (BZP) compared to its solution phase emission in any good solvent. This exceptional blue emission from aggregated structure of BZP arises from its locally excited states with the concomitant suppression of twisted intramolecular charge transfer (TICT) motion. This is known as aggregation induced locally excited (AILE) state emission. A broad red shifted emission is also observed in case of larger aggregated structure of BZP and it originates from the excited intramolecular charge transfer (ICT) state of planar BZP. Morphology of the aggregated BZP is also studied by scanning electron microscopy and optical microscopy. This AILE emission of the luminogen is used for sensing glucose in aqueous solution at very low concentration. The quenching of AILE in presence of glucose has been explained due to hydrogen bonded complexation between glucose and BZP molecule present at the surface of the aggregated structure and is responsible for crystal softening, i.e. loosening of crystal packing.