On infinitenes – Reliable calculation of λ∞ and molecular modeling of lemniscate structured carotenoids

• Published in: Computational and theoretical chemistry 2018-02, Vol.1125, p.133-141
• Main Authors: Martínez, Ana, Zeeshan, Muhammad, Zaidi, Asma, Sliwka, Hans-Richard, Razi Naqvi, K., Partali, Vassilia
• Format: Article
• Language: English
• Subjects: Carotenoids; DFT calculation; Polyenes; UV/VIS spectroscopy
• ISSN: 2210-271X
• DOI: 10.1016/j.comptc.2017.12.006

Accumulating “infinite” conjugated double bonds in carotenoids imparts to the molecule the shape of a lemniscate, the symbol for infinity. The name infinitene is proposed for a hypothetical lemniscate carotenoid. [Display omitted] •Molecular modeling of elongated carotenoids.•Calculating λ∞ of infinite elongated carotenoids by an improved empirical formula.•Calculating λmax by DFT.•Lemniscate structure are found for very long carotenoids.•Infinitenes as new compounds. The absorption limit for an “infinite” number of conjugated double bonds has been a topic of considerable interest for over seventy years. Establishing the limit (hereafter λ∞) consists in collecting the spectral data of homologous polyenes (in most previous investigation with ≤17 double bonds), fitting the absorption values to a formula with one or more adjustable parameters, and identifying λ∞ by extrapolation. Here we report establishing the unsettled value of λ∞ by taking as basis three recently synthesized long carotenoid families culminating in 19, 23 and 27 conjugated double bonds. Excellent fits of experimental data have been obtained by using new formulas allowing a confident λ∞-extrapolation to carotenoids with infinite length. UV–visible λmax values of long carotenoids were also calculated by using Time Dependent Density Functional Theory (TDDFT). The theoretical results agree well with the experimental trend. Molecular modeling confirmed that accumulating “infinite” conjugated double bonds in carotenoids imparts to the molecule the shape of a lemniscate, the symbol for infinity. The name infinitene is proposed for a hypothetical lemniscate carotenoid.