Shape-tunable two-dimensional assemblies from chromophore-conjugated crystallizable poly(L-lactides) with chain-length-dependent photophysical properties

This work reports temperature-dependent shape-changeable two-dimensional (2D) nanostructures by crystallization-driven self-assembly (CDSA) from a chromophore-conjugated poly(L-lactide) (PLLA) homopolymer (PTZ-P1) that contained a polar dye, phenothiazine (PTZ), at the chain-end of the crystallizable PLLA. The CDSA of PTZ-P1 in a polar solvent, isopropanol (iPrOH), by an uncontrolled heating-cooling process, majorly generates lozenge-shaped 2D platelets via chain-folding-mediated crystallization of the PLLA core, leading to the display of the phenothiazines on the 2D surface that confers colloidal stability and orange-emitting luminescent properties to the crystal lamellae. Isothermal crystallization at 60 °C causes a morphological change in PTZ-P1 platelets from lozenge to truncated-lozenge to perfect hexagon under different annealing times, while no shape change was noticed in the structurally similar PTZ-P2 polymer with a longer PLLA chain under similar conditions. This study unveils the complex link between the 2D platelet morphologies and degree of polymerization (DP) of PLLA and the corona-forming dye character. Further, the co-assembly potential of PTZ-P1 with hydrophobic pyrene-terminated PLLAs of varying chain lengths (PY-P1, PY-P2, and PY-P3) was examined, as these two dyes could form a Förster Resonance Energy Transfer (FRET) pair on the 2D surface. The impact of the length of the crystallizable PLLA on the photophysical properties of the surface-occupied chromophores revealed crucial insights into interchromophoric interactions on the platelet surface. A reduction in the propensity for π-stacking with increasing chain-folding in longer PLLAs is manifested in the chain-length-dependent FRET efficiencies and excimer emission lifetimes within the resultant monolayered 2D assemblies. The unconventional "butterfly-shaped" molecular architecture of the tested phenothiazine, combined with its varied functional features and polar character, adds a distinctive dimension to the underdeveloped field of CDSA of chromophore-conjugated poly(L-lactides), opening future avenues for the development of advanced nanostructured biodegradable 2D materials with programmable morphology and optical functions.

Cascade Energy Transfer and White-Light Emission in Chirality-Controlled Crystallization-Driven Two-Dimensional Co-assemblies from Donor and Acceptor Dye-Conjugated Polylactides

Achieving predictable and programmable two-dimensional (2D) structures with specific functions from exclusively organic soft materials remains a scientific challenge. This article unravels stereocomplex crystallization-driven self-assembly as a facile method for producing thermally robust discrete 2D-platelets of diamond shape from biodegradable semicrystalline polylactide (PLA) scaffolds. The method involves co-assembling two PLA stereoisomers, namely, PY-PDLA and NMI-PLLA, which form stereocomplex (SC)-crystals in isopropanol. By conjugating a well-known Förster resonance energy transfer (FRET) donor and acceptor dye, namely, pyrene (PY) and naphthalene monoimide (NMI), respectively, to the chain termini of these two interacting stereoisomers, a thermally robust FRET process can be stimulated from the 2D array of the co-assembled dyes on the thermally resilient SC-PLA crystal surfaces. Uniquely, by decorating the surface of the SC-PLA crystals with an externally immobilized guest dye, Rhodamine-B, similar diamond-shaped structures could be produced that exhibit pure white-light emission through a surface-induced two-step cascade energy transfer process. The FRET response in these systems displays remarkable dependence on the intrinsic crystalline packing, which could be modulated by the chirality of the co-assembling PLA chains. This is supported by comparing the properties of similar 2D platelets generated from two homochiral PLLAs (PY-PLLA and NMI-PLLA) labeled with the same FRET pair.

Impact of polymer chain packing and crystallization on the emission behavior of curcumin-embedded poly(L-lactide)s

The development of biodegradable and biocompatible fluorescent materials with tunable emission in the solid state has become increasingly relevant for smart packaging and biomedical applications. Molecular packing and conformations play a critical role in tuning the solid-state photophysical properties of fluorescent materials. In this work, tunable emission of bioactive curcumin was achieved through the manipulation of the crystallization conditions and the polymorphic form of covalently linked poly(L-lactide) in the curcumin-embedded poly(L-lactide) (curcumin-PLLA). In the melt-crystallized curcumin-PLLA, with the increase in the isothermal crystallization temperature, a bathochromic shift in the fluorescence of curcumin-PLLA was observed due to the change in the intramolecular conjugation length of curcumin. The change in the isothermal crystallization temperature of curcumin-PLLA resulted in the rotation of the terminal phenyl rings of curcumin with respect to the central keto-enol group due to the covalently linked helical PLLA chains. In addition, solvent-induced single crystals and a gel of curcumin-PLLA were prepared and the influence of the polymorphic form of PLLA on the emission behavior of curcumin-PLLA was investigated. The results suggest that the polymer chain packing, crystallization conditions, morphology, and polymorphic form could play an influential role in dictating the fluorescence properties of fluorophore-embedded polymers.

Controlling the Fluorescence Performance of AIE Polymers by Controlling the Polymer Microstructure

Aggregation-induced emission (AIE) polymers with expected emission wavelength/color and fluorescence efficiency are valuable in applications. However, most AIE polymers exhibit irregular emission wavelength/color changes compared to the original AIE monomers. Here, we report the synthesis of AIE polymers with unchanged emission wavelength by ring-opening (co)polymerizations of 4-(triphenylethenyl)phenoxymethyloxirane (TPEO) and other epoxides or phthalic anhydride. The chemical structures/physical properties of all (co)polymers were characterized by NMR, SEC, MALDI-TOF, and DSC. The co-polyether microstructures were revealed by calculating the reactivity ratios and visualized by Monte Carlo simulation. The photoluminescence quantum yields of all the (co)polymers were determined in the solid state. We systematically correlated the fluorescence performance with molecular weights, crystallinity, monomer compositions, glass transition temperatures, side lengths, and flexibility/rigidity.

Dual-Color Emission from Spatially Distributed Quantum Dots in Poly(l-lactide) Films with Diverse Morphologies

Polymer-based multicolor emissive materials have growing demand due to their potential applications in various fields such as full-color displays, bioimaging, and light sources because of their processability and high stability. Herein, we report dual-color emissive hybrid materials based on biocompatible poly(l-lactide) and polyethylene glycol-modified two-dimensional layered double hydroxide quantum dots (PEG-LDHQDs). The morphology of polymer films tunes the spatial distribution of QDs within the polymer matrix, modulating the energy transfer between the QDs and affording the dual emission behavior in the aggregated states. The amorphous hybrid films show single emission (blue) from the finely dispersed QDs (mostly isolated) within the polymer matrix. In contrast, dual emission (blue and red) was observed when the polymer was crystallized due to the possible accumulation of QDs at the interface of crystalline and amorphous phases in the lamellar structure. Furthermore, the dual emission could be enhanced by the aggregation of QDs on the pores of the breath figure pattern constructed on the surface of the hybrid film.

Fluorescent and stimuli-responsive performance of polymer composites filled with tetraphenylethene derivatives

In this study, a series of tetraphenylethene (TPE) derivatives with 3-butenloxy moieties were synthesized. The developed TPE with different number of substituent groups showed controlled aggregation-induced emission performance and variable...