Light-Up of Rhodamine Hydrazide to Generate Emissive Initiator for Polymerization and to Afford Photochromic Polypeptide Metal Complex.

Jhen-Yan Gao,Pei-Yi Huang,Cheng-Yu Song,Wen-Chih Huang,Jin-Long Hong

doi:10.3390/polym9090419

Abstract

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.

Highlights

Rhodamine derivatives belong to a class of the most popular luminescent dyes with long-wavelength absorption, high absorption coefficient and quantum efficiency, and good photostability in the solution state
Rhodamine dyes were widely used in industrial coloration, biomarkers, molecular biology and as photosensitizers in dye-sensitized solar cells, dye laser, etc. [1,2,3,4,5,6,7,8,9]
The first rhodamine-based luminogen of bisbenzofuran-bisbenzopyrano-xanthene derivative [16] with aggregation-induced emission (AIE) [17,18,19,20,21,22,23] properties was developed since its inherent rhodamine units can be in the confined, aggregated state

Summary

Introduction

Rhodamine derivatives belong to a class of the most popular luminescent dyes with long-wavelength absorption, high absorption coefficient and quantum efficiency, and good photostability in the solution state. (Rh–C, Scheme 1) suggested that the imidate anion (–C(–O− )=N–) of ring-open Rh–O is responsible for the photochromism. Because of short lifetime and low quantum efficiency of the photoinduced reaction, few investigations [26,27,28,29] were aimed at the photochromic properties of rhodamine amides over the 30 years. Recent progress suggested that metal complex (RhM–C, Scheme 1) of rhodamine B salicylaldehyde hydrazine [30] exhibited long lifetime and good fatigue resistance. Metal complexes exhibited photochromism with a long RhM–O lifetime[30], of R–PLG.

Conversion of ring-close

Results and Discussion

Solid FTIR spectra of pure R-C and the quenched oligomer from the

Emissive

Because

Conclusions