Computational and experimental studies on the micellar morphology and emission mechanisms of AIE and H-bonding fluorescent composites

In this work, we use density functional theory (DFT) calculated competitive hydrogen bonds and dissipative particle dynamics (DPD) simulated micellar structural information to uncover the CO2-expanded liquid (CXL)-aided self-assembled structure and emission mechanisms of the self-assembled fluorescent composites (SAFCs). Herein, the SAFCs are formed through the self assembly between diblock copolymer polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) blend and the dye molecule 4-(9-(2-(4-hydroxyphenyl)ethynyl)-7,10-diphenylfluoranthen-8-yl)phenol (4) in CO2-expanded toluene at 313.2 K and varied pressures. Firstly, from DPD simulation, we have demonstrated that the addition of CO2 to toluene favors both the expansion of the solvophobic P4VP phase and contraction of solvophilic PS chains, which facilitates the continuous morphological transitions of SAFCs from spherical micelles (3.0 MPa) through wormlike plus spherical micelles (4.0-4.8 MPa) to large vesicles (6.0-6.5 MPa) with pressure rise. Secondly, the DFT calculated bonding energies and IR spectra of the competitive hydrogen bonds help us to clarify the major type of hydrogen bonds determining the fluorescence (FL) performance of the SAFCs. Furthermore, we have revealed the SAFC emission mechanism via the pressure-tunable changes in the aggregation degrees and amount of hydrogen bonds involving 4 and P4VP chains. This work provides a good understanding for the morphology-property control of the self-assembled polymer composites in both microscopic and mesoscopic scales.

Synthesis, micellar structures and emission mechanisms of an AIE and DDED-featured fluorescent pH- and thermo-meter

A new nanoprobe, the luminescent diblock copolymer PNIPAM(MAh-4)-b-P4VP (PN4P), with pH- and thermo-responsive deprotonation-driven emission decay (DDED) and aggregation-induced emission (AIE) features was designed and synthesized. The nanoprobe PN4P can form micellar structures in water with reversible dual-responsive fluorescence (FL) behavior within a wide pH range of 2–11. The critical solution temperature was found at about 32, 30 and 27 °C as the pH switched from 2, 7 to 11. The critical pH value of the probe was about 4.0, and the micelles showed a core–shell inversion in response to pH and thermal stimuli, accompanied by a desirable emission tunability. P4VP as the micellar shell at pH = 2 was more easily dehydrated with the increase in temperature as compared to PNIPAM as the micellar shell at pH > 4. The strongest dehydration of the P4VP shell would make PN4P the most strongly aggregated and the most AIE-active, which supports the 2.10-fold most distinguished thermal-responsive emission enhancement at pH = 2. Moreover, a dramatic acidochromic redshift of the emission band from 450 (pH > 4) to 490 nm (pH = 2) was observed, and the maximum emission at pH = 2 was enhanced by about 2.07-fold as compared with that at pH = 7. Therefore, the probe displays the desired dual responses and good reversibility. AIE and DDED are the two major mechanisms responsible for the dual-responsive emission change, with AIE playing a more important role than DDED. This work offers a promising approach to interpreting temperature (range from 28 to 40 °C) and pH changes (range from 2 to 7) in water.

A nanoprobe in water features pH- and thermal-responsive micellar/clustering structures, deprotonation-driven emission decay (DDED) and aggregation-induced emission (AIE).