Raman Optical Activity (ROA) as a New Tool to Elucidate the Helical Structure of Poly(phenylacetylene)s

This is the peer reviewed version of the following article: L. Palomo, R. Rodríguez, S. Medina, E. Quiñoá, J. Casado, F. Freire, F. J. Ramírez, Angew. Chem. Int. Ed. 2020, 59, 9080, which has been published in final form at https://doi.org/10.1002/anie.202000651. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived VersionsPoly(phenylacetylene)s are a family of helical polymers constituted by conjugated double bonds. Raman spectra of these polymers show a structural fingerprint of the polyene backbone which, in combination with its helical orientation, makes them good candidates to be studied by Raman optical activity (ROA). Four different well‐known poly(phenylacetylene)s adopting different scaffolds and ten different helical senses have been prepared. Raman and ROA spectra were recorded and allowed to establish ROA‐spectrum/helical‐sense relationships: a left/right‐handed orientation of the polyene backbone (Mhelix/Phelix) produces a triplet of positive/negative ROA bands. Raman and ROA spectra of each polymer exhibited the same profile, and the sign of the ROA spectrum was opposite to the lowest‐energy electronic circular dichroism (ECD) band, indicating a resonance effect. Resonance ROA appears then as an indicator of the helical sense of poly(phenylacetylene)s, especially for those with an extra Cotton band in the ECD spectrum, where a wrong helical sense is assigned based on ECD, while ROA alerts of this misassignmentFinancial support from MINECO (PGC2018‐098533‐B‐I00 and the Junta de Andalucía project reference (UMA18‐FEDERJA‐057) are acknowledged. Xunta de Galicia (ED431C 2018/30, Centro singular de investigación de Galicia accreditation 2016–2019, ED431G/09 and postdoctoral fellowship for R.R.) and the European Regional Development Fund (ERDF) are also gratefully acknowledgedS