Construction of two rosin-based BioAIEgens with distinct fluorescence and mechanochromic propertites for rewritable paper

Abstract

Mechanochromic materials have been attractive to researchers in recent years due to their wide applications. However, traditional petrochemical-based mechanochromic materials are probably faced with problems of non-renewability and poor sustainability. Hence, it is of great significance to develop mechanochromic materials from phytochemicals endowed with renewability and sustainability. Herein, after combining the tetraphenylethene motif with a rosin-originated phytochemical, dehydroabietic acid, two natural rosin-based aggregation-induced emission (BioAIE) luminogens, DAA-TPE and DAMBA-TPE, were separately obtained on distinct Schiff base reaction sites. Both compounds have AIE phenomena mainly due to the introduction of tetraphenylethene group. However, their other optical properties are totally different depending on the imine site. DAMBA-TPE (imine on the aromatic site of dehydroabietic acid) shows very weak fluorescence at aggregate state, while DAA-TPE (imine on the alkyl site of dehydroabietic acid) exhibits strong emission and high contrast mechanochromic behavior in the solid state. Via the introduction of naturally large alkyl substitution, the pristine powder can be illuminated with a red shift of 28 nm from blue (442 nm) to cyan (470 nm) upon grinding. While a structurally analogue with a small iso-butyl substitution does not possess mechanochromism. Moreover, the fluorescence of DAA-TPE can be reversibly switched, which is most probably attributed to the crystal form change before and after grinding. This property endows DAA-TPE with potential application in the manufacturing of rewritable paper. Last but not least, this work paves a way to the design of mechanochromic materials from naturally renewable resources via introduction of large alkyl groups on the TPE skeleton.