title: Photogenerated cumulenic structure of adamantyl endcapped linear carbon chains: an experimental and computational investigation based on infrared spectroscopy.
abstract: The infrared (IR) spectrum of an adamantyl endcapped α, ω-polyyne (the hexayne, Ad-C(12)-Ad) is investigated both experimentally and computationally. A new IR band is observed upon UV photoexcitation of the compound (embedded in a poly methyl methacrylate matrix at 78 K), thus, revealing the existence of new photogenerated molecular structure trapped at low temperature. Complete reversibility is found, thus, demonstrating that the photoexcitation is responsible for the generation of metastable excited states of the molecule. Density functional theory and time dependent density functional theory calculations indicate that these metastable states result from the forbidden singlet (S(1)) or triplet (T(1)) excited states, and geometry optimizations of the polyyne trapped in either S(1) and/or T(1) states demonstrate that the carbon chain takes on a cumulenic structure. Comparison of the experimental and the computed IR spectra for the molecule trapped in the forbidden states confirms that the new IR features are clear markers of cumulenic species. The temperature and time dependent behavior of the new IR band is analyzed, while the experimentally determined value of the activation energy highlights the low stability of these molecular structures.
authors: Dipartimento di Chimica, Materiali e Ing. Chimica G. Natta, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milano, Italy.
authors: Melike Mercan
authors: MM
authors: Yildizhan
authors: Daniele
authors: D
authors: Fazzi
authors: Alberto
authors: A
authors: Milani
authors: Luigi
authors: L
authors: Brambilla
authors: Mirella
authors: M
authors: Del Zoppo
authors: Wesley A
authors: WA
authors: Chalifoux
authors: Rik R
authors: RR
authors: Tykwinski
authors: Giuseppe
authors: G
authors: Zerbi