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Near-Ultraviolet Circular Dichroism of Achiral Phenolic Termini Induced by Nonchromophoric Poly(l,l‑lactide) and Poly(d,d‑lactide)

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journal contribution
posted on 11.08.2016 by Kai Kan, Michiya Fujiki, Mitsuru Akashi, Hiroharu Ajiro
Herein, we present the first induced chirality of vanillin and its phenolic analogs attached to the chain ends of poly­(l,l-lactide) and poly­(d,d-lactide). Vanillin analogs were used as chromophoric and luminophoric, but achiral, ring-opening initiators of corresponding chiral cyclic lactides. Induced chirality was evident from clear circular dichroism bands at 270–320 nm due to π–π* and n−π* transitions at the vanillin moiety. However, no circularly polarized luminescence band was detected. Density functional theory (DFT) and time-dependent DFT calculations suggested the existence of multiple through-space intramolecular CH/O interactions between the ortho-methoxy moiety of vanillin and nearest-neighbor lactic acid units. The terminus sensitively indicated whether the main-chain chirality was l or d.