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1.
J Am Chem Soc ; 141(23): 9273-9283, 2019 Jun 12.
Artigo em Inglês | MEDLINE | ID: mdl-31091876

RESUMO

We report a novel class of star-shaped multiazobenzene photoswitches comprising individual photochromes connected to a central trisubstituted 1,3,5-benzene core. The unique design of such C3-symmetric molecules, consisting of conformationally rigid and pseudoplanar scaffolds, made it possible to explore the role of electronic decoupling in the isomerization of the individual azobenzene units. The design of our tris-, bis-, and mono(azobenzene) compounds limits the π-conjugation between the switches belonging to the same molecule, thus enabling the efficient and independent isomerization of each photochrome. An in-depth experimental insight by making use of different complementary techniques such as UV-vis absorption spectroscopy, high performance liquid chromatography, and advanced mass spectrometry methods as ion mobility revealed an almost complete absence of electronic delocalization. Such evidence was further supported by both experimental (electrochemistry, kinetical analysis) and theoretical (DFT calculations) analyses. The electronic decoupling provided by this molecular design guarantees a remarkably efficient photoswitching of all azobenzenes, as evidenced by their photoisomerization quantum yields, as well as by the Z-rich UV photostationary states. Ion mobility mass spectrometry was exploited for the first time to study multiphotochromic compounds revealing the occurrence of a large molecular shape change in such rigid star-shaped azobenzene derivatives. In view of their high structural rigidity and efficient isomerization, our multiazobenzene photoswitches can be used as key components for the fabrication of complex stimuli-responsive porous materials.

2.
J Am Chem Soc ; 140(47): 16062-16070, 2018 Nov 28.
Artigo em Inglês | MEDLINE | ID: mdl-30380853

RESUMO

We report the synthesis of a novel C3-symmetrical multiphotochromic molecule bearing three azobenzene units at positions 1, 3, 5 of the central phenyl ring. The unique geometrical design of such a rigid scaffold enables the electronic decoupling of the azobenzene moieties to guarantee their simultaneous isomerization. Photoswitching of all azobenzenes in solution was demonstrated by means of UV-vis absorption spectroscopy and high performance liquid chromatography (HPLC) analysis. Scanning tunneling microscopy investigations at the solid-liquid interface, corroborated by molecular modeling, made it possible to unravel the dynamic self-assembly of such systems into ordered supramolecular architectures, by visualizing and identifying the patterns resulting from three different isomers, thereby demonstrating that the multiphotochromism is retained when the molecules are confined in two dimensions.

3.
Chemistry ; 24(7): 1631-1639, 2018 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-29112319

RESUMO

Four tetradithienylethene (DTE) substituted porphyrins, the free base 1H2 , and three metal derivatives (1Zn, 1Co, 1Ni), were synthesized and studied. These dyads, for which the DTE units are connected to the porphyrin's meso positions via a meta-phenyl spacer, exhibit reversible photochromic properties in all cases, with conversion to the photostationary state (PSS) up to 88 %, as confirmed by absorption and NMR spectroscopies. Compounds 1H2 and 1Zn are fluorescent in solution and display a red emission. Upon irradiation with UV light to trigger the closing of the DTEs, the fluorescence of both the free base and zinc porphyrin was very efficiently quenched in solution. The reversible, photo-switching of luminescence was retained in a tetra-DTE free-base porphyrin-doped polystyrene film, for which photo-patterning was demonstrated by confocal scanning microscopy. The tunable fluorescent properties of this multi-DTE framework render this compound of interest as a photo-rewritable fluorescent ink.

4.
Chem Commun (Camb) ; 53(53): 7278-7281, 2017 Jun 29.
Artigo em Inglês | MEDLINE | ID: mdl-28425541

RESUMO

The functionalization of a spherical Keplerate-type polyoxometalate {Mo72V30} with a cationic azobenzene surfactant has been achieved through ionic self-assembly. The photoisomerisation reaction of this complex, which emerges in a light-triggered aggregation-disaggregation process, has been followed by 1H NMR spectroscopy, dynamic light scattering, absorption spectroscopy and scanning electron microscopy analyses.

5.
Chemistry ; 22(28): 9709-23, 2016 Jul 04.
Artigo em Inglês | MEDLINE | ID: mdl-27258206

RESUMO

Here we have investigated the influence of the antenna group position on both the formation of chiral amphiphilic Eu(III) -based self-assemblies in CH3 CN solution and, on the ability to form monolayers on the surface of quartz substrates using the Langmuir-Blodgett technique, by changing from the 1-naphthyl (2(R), 2(S)) to the 2-naphthyl (1(R), 1(S)) position. The evaluation of binding constants of the self- assemblies in CH3 CN solution was achieved using conventional techniques such as UV/Visible and luminescence spectroscopies along with more specific circular dichroism (CD) spectroscopy. The binding constants obtained for EuL, EuL2 and EuL3 species in the case of 2-naphthyl derivatives were comparable to those obtained for 1-naphthyl derivatives. The analysis of the changes in the CD spectra of 1(R) and 1(S) upon addition of Eu(III) not only allowed us to evaluate the values of the binding constants but the resulting recalculated spectra may also be used as fingerprints for assignment of the chiral self-assembly species formed in solution. The obtained monolayers were predominantly formed from EuL3 (≈85 %) with the minor species present in ≈15 % EuL2 .

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