Crystallization-driven precision two-dimensional (2D) assemblies from chromophore-conjugated poly(lactide)s Anindita Das Indian Association for the Cultivation of Science, Kolkata, India Aliphatic polyesters are considered a sustainable alternative to petroleum-based polymers due to their biodegradability. Some of them, such as polylactic acids, polycaprolactone, etc., have been extensively explored in biological applications as delivery vehicles for their additional biocompatibility. Although these polymers can be easily synthesized from commercially available cyclic lactides and lactones by ring opening polymerization (ROP), they have limited properties due to the lack of tuneable side chain functionalities. Moreover, being hydrophobic, they need to be conjugated with different hydrophilic moieties for studying their self-assembly in water. Our group has established a versatile and generally applicable condensation polymerization methodology for the synthesise of functional aliphatic polyesters.1 The synthesis involves the transesterification of activated bis(pentafluorophenyl) adipate with functional diols in the presence of an organocatalyst, 4-dimethylaminopyridine (DMAP). 1 This methodology eliminates the need to remove by-products, which is still a significant challenge in the production of conventional polyesters using non-activated diesters. Following this methodology, positively charged, fluorescent aromatic pendant moieties with variation in hydrophobic chain lengths were incorporated to synthesize enzymatically degradable water-soluble polyesters, which show great potential as broad-spectrum antibacterial agents. 2 In another area, we have explored the well-known crystallization-driven self-assembly (CDSA) 3 of a biodegradable aliphatic polyester, poly-L-lactide (PLLA) to achieve structurally and functionally diverse precision two-dimensional (2D) assemblies in a crystallizable solvent (isopropanol). PLLA homopolymers, end-functionalized with different dipolar chromophores such as merocyanine (MC) or naphthalene monoimide (NMI) and nonpolar pyrene (PY) or benzene (Bn), crystallize into precise diamond-shaped 2D platelets in isopropanol. 4 This causes the terminally attached chromophores to assemble into a 2D array on the platelet surface by either dipole-dipole interactions (for NMI and MC) or aromatic stacking (PY and Bn), which leads to aggregation-induced enhanced emission (AIEE) with tuneable emission wavelengths within the 2D crystals, depending upon the nature of the end-capped chromophores.4 Further, co-assembly between NMI- and PY-functionalized PLLAs yielded similar two-component co-platelets with highly efficient Förster resonance energy transfer (FRET) from the donor (PY) to the acceptor (NMI) dye with remarkable efficiency (~80%) on the 2D surface. Further, by incorporating the same donor and acceptor dyes at the chain ends of the two enantiomers (PLLA and PDLA), we were able to monitor the stereo- complex co-crystallization in the solution phase by FRET studies, whose similar diamond-shaped 2D structure showed enhanced stability as compared to the individual homo-platelets.5 Furthermore, we studied the scope of these SC co-crystals for surface decoration with external fluorescent dyes for cascade energy transfer and white light emission. 5 Various aspects of these two topics will be covered in the talk. References 1. Biswas, S.; Das, A.* Chem. Eur. J. 2023. 29, e202203849. 2. Biswas, S.; Barman, R.; Das, A.* manuscript under preparation 3. MacFarlane, L.; Zhao, C.; Cai, J.; Qiu, H.*; Manners, I.* Chem. Sci. 2021, 12, 4661-4682. 4. Rajak, A.; Das, A.* Angew. Chem. Int. Ed. 2022, 61, e202116572. (Selected as a Hot Paper and Cover Picture). 5. Rajak, A.; Das, A.* Angew. Chem. Int. Ed. 2023 (doi.org/10.1002/anie.202314290).
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