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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, 16:04 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.