AIE-related emission of polypeptide containing an AIE-active terminal is correlated with secondary structures (α-helix, β-sheet and random coil) of the peptide chains.
Ring-opening polymerization (ROP) of cyclic peptide monomer of γ-propargyl-L-glutamate N-carboxyanhydride (PLG-NCA) was originally initiated by non-emissive, ring-close rhodamine 6G hydrazide (R-C). However, instantaneously after adding PLG-NCA to R-C, the spirolactam ring of R-C was opened by PLG-NCA, rendering emissive, ring-open R-O to initiate ROP of PLG-NCA. The emissive R-O moiety therefore produced fluorescent R-PLG with aggregation-induced emission (AIE) properties. Moreover, R-PLG was found to exhibit photochromic properties with good fatigue resistance and long lifetime when forming metal complexes with Sn(II) and Fe(III). In the dark, irradiated metal complexes slowly (~50 min) restored to the initial state. This research provides foundation for the development of new photochromic materials with long lifetime.
Bulky camphorsulfonic acid (CSA) was used to complex with quinine (Qu) to impose restricted intramolecular rotation (RIR) required for aggregation-induced emission (AIE) properties.
An AIE-active rhodamine based luminogen was prepared via a complexation reaction between non-emissive rhodamine hydrazide (RdH) and bulky camphorsulfonic acid (CSA). Besides acting to open the spirolactam ring of RdH, CSA also imposes a rotational restriction on the resultant ionic complex, RdH(CSA). Without CSA, the analogous complex RdH(HCl) is a luminogen with aggregation-caused quenching (ACQ) properties. The ionic bonds of RdH(CSA) are sensitive to several external stimuli and therefore it is a luminescent sensor for metal ions, organic amines and the blood protein bovine serum albumin (BSA). Besides being a sensor for BSA, the ionic RdH(CSA) is also a denaturant capable of uncoiling the peptide chain of BSA.
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