Tuning the fluorescence of aggregates for end-functionalized polymers through varying polymer chains with different polarities

Abstract

In the past several decades, a great deal of attention has been focused on the control of light emission of luminescent materials. Compared to our previous work on an aggregation-induced emission (AIE) initiator, an aggregation-caused quenching (ACQ) initiator (TPP-A) has been successfully synthesized and acted as an initiator of atom transfer radical polymerization (ATRP). Four end-functionalized polymers, PS-A, PS-NI, PNIPAM-A and PNIPAM-NI, were obtained using TPP-A or TPP-NI as an initiator via ATRP. TPP-A exhibits a weak charge transfer (CT) and ACQ, but TPP-NI possesses a strong CT and AIE. After two initiators were introduced to polystyrene (PS) chains, the CT of PS-A and PS-NI are well-preserved, but their photoluminescence (PL) intensity is increased because the PS chains could separate initiators from intermolecular interactions and restrict their intramolecular rotations. However, the emission behaviours of PNIPAM-A are different from those of PS-A due to the high polarity of the PNIPAM chain. When the temperature of the solution for PNIPAM-A is above the lower critical solution temperature (LCST), the PNIPAM-A solution possessed higher emission intensities than those measured at room temperature due to the decrease the polarity of the PNIPAM chain and the emission behaviours of PNIPAM-NI are similar to that of PS-NI.