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Tailoring Photoisomerization Pathways in Donor-Acceptor Stenhouse Adducts: The Role of the Hydroxy Group

  Articoli su Riviste JCR/ISI  (anno 2018)

Autori:  Lerch MM., Medved M., Lapini A., Laurent AD., Iagatti A., Bussotti L., Szymanski W., Buma WJ., Foggi P., Di Donato M., Feringa B

Affiliazione Autori:  [Lerch, Michael M.; Szymanski, Wiktor; Feringa, Ben L.] Univ Groningen, Stratingh Inst Chem, Ctr Syst Chem, Nijenborgh 4, NL-9747 AG Groningen, Netherlands. [Szymanski, Wiktor] Univ Groningen, Univ Med Ctr Groningen, Dept Radiol, Hanzepl 1, NL-9713 GZ Groningen, Netherlands. [Lapini, Andrea; Iagatti, Alessandro; Bussotti, Laura; Foggi, Paolo; Di Donato, Mariangela] LENS European Lab Non Linear Spect, Via N Carrara 1, I-50019 Sesto Fiorentino, Italy. [Iagatti, Alessandro; Foggi, Paolo; Di Donato, Mariangela] INO, Largo Fermi 6, I-50125 Florence, Italy. [Lapini, Andrea] Univ Firenze, Dipartimento Chim Ugo Schiff, Via Lastruccia 13, I-50019 Sesto Fiorentino, Italy. [Foggi, Paolo] Univ Perugia, Dipartimento Chim, Via Elce Sotto 8, I-06100 Perugia, Italy. [Medved, Miroslav] Palacky Univ, Fac Sci, Dept Phys Chem, Reg Ctr Adv Technol & Mat, 17 Listopadu 1192-12, CZ-77146 Olomouc, Czech Republic. [Medved, Miroslav] Matej Bel Univ, Fac Nat Sci, Dept Chem, Tajovskeho 40, SK-97400 Banska Bystrica, Slovakia. [Laurent, Adele D.] CEISAM, UMR CNRS 6230, BP 92208,2 Rue Houssiniere, F-44322 Nantes 3, France. [Buma, Wybren Jan] Univ Amsterdam, Vant Hoff Inst Mol Sci, Sci Pk 904, NL-1098 XH Amsterdam, Netherlands.

Riassunto:  Donor-acceptor Stenhouse adducts (DASAs) arc a rapidly emerging class of visible light-activatable negative photochromes. They are closely related to (mero)cyanine dyes with the sole difference being a hydroxy group in the polyene chain. The presence or absence of the hydroxy group has far-reaching consequences for the photochemistry of the compound: cyanine dyes are widely used as fluorescent probes, whereas DASAs hold great promise for visible light-triggered photoswitching. Here we analyze the photophysical properties of a DASA lacking the hydroxy group. Ultrafast time-resolved pump-probe spectroscopy in both the visible and IR region show the occurrence of E-Z photoisomerization on a 20 ps time scale, similar to the photochemical behavior of DASAs, but on a slower time scale. In contrast to the parent DASA compounds, where the initial photoisomerization is constrained to a single position (next to the hydroxy group), H-1 NMR in situ-irradiation studies at 213 K reveal that for nonhydroxy DASAs E-Z photoisomerization can take place at two different bonds, yielding two distinct isomers. These observations arc supported by TD-DFT calculations, showing that in the excited state the hydroxy group (pre)selects the neighboring C2-C3 bond for isomerization. The TD-DFT analysis also explains the larger solvatochromic shift observed for the parent DASAs as compared to the nonhydroxy analogue, in terms of the dipole moment changes evoked upon excitation. Furthermore, computations provide helpful insights into the photoswitching energetics, indicating that without the hydroxy group the 4 pi-electrogclization step is energetically forbidden. Our results establish the central role of the hydroxy group for DASA photoswitching and suggest that its introduction allows for tailoring photoisomerization pathways, presumably both through (steric) fixation via a hydrogen bond with the adjacent carbonyl group of the acceptor moiety, as well as through electronic effects on the polyene backbone. These insights are essential for the rational design of novel, improved DASA photoswitches and for a better understanding of the properties of both DASAs and cyanine dyes.

Volume n.:  122 (4)      Pagine da: 955  a: 964
DOI: 10.1021/acs.jpca.7b10255

   *Citazioni: 5
data tratti da "WEB OF SCIENCE" (marchio registrato di Thomson Reuters) ed aggiornati a:  19/05/2019

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