Towards a spectroscopic and structural understanding of indigo: Dye widely used during the ancient and Islamic periods

Towards a spectroscopic and structural understanding of indigo: Dye widely used during the ancient and Islamic periods | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Towards a spectroscopic and structural understanding of indigo: Dye widely used during the ancient and Islamic periods Nouhaila HILALI, Taibi LAMHASNI, Fatima Zahra BOUCHOUAF, Salma ATEF, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8449741/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Indigo is one of the most famous and important dyes and is found in different heritage materials such as carpets, textiles, artworks, manuscripts, etc. However, until now, scientists never understood its spectroscopic behavior in heritage materials. Indeed, some bands or peaks undergo important shifts and others sometimes disappear. Thus, our objectives consist of multi-technical fingerprinting of this very important dye and elucidating its spectroscopic behavior. To achieve our objectives, several calculation methods have been applied and the obtained results are compared to77 experimental data. The correlation between the spectroscopic and structural properties revealed that: i) During the dyeing process, the Indigo molecule would undergo trans-cis photoisomerization thereby causing the rupture of the two intramolecular hydrogen bonds, followed by a dimerization process occurring through the establishment of two new intermolecular hydrogen bonds connecting the two monomers. ii) In heritage materials, the absence of indigo fluorescence is due most probably to the quenching phenomenon. iii) In the Raman spectrum, the shift in C = C vibration values (theoretical and experimental) is likely due to intermolecular interactions. Physical sciences/Chemistry Physical sciences/Materials science Indigo UV-Vis FTIR Raman Photoisomerization Dimerization Full Text Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8449741","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":576668754,"identity":"f75ce807-91c1-4cfb-af84-15126576aeae","order_by":0,"name":"Nouhaila HILALI","email":"","orcid":"","institution":"National Institute of Archaeology and Heritage Sciences (INSAP)","correspondingAuthor":false,"prefix":"","firstName":"Nouhaila","middleName":"","lastName":"HILALI","suffix":""},{"id":576668769,"identity":"f7ee6992-31cd-4f23-abdd-38e227ac0617","order_by":1,"name":"Taibi 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