Guest–guest interactions in urea inclusion compounds †

Brustolon, Marina; Maniero, Anna Lisa; Segre, Ulderico

doi:10.1039/a702492d

Cited by 7 publications

(4 citation statements)

References 15 publications

(19 reference statements)

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“…The dynamics of included polymers and elongated molecules forming high-melting nanocomposites is particularly intriguing and promotes anisotropic motions and mesophases . EPR spectroscopies have been applied to stable nitroxide radicals included as guests in zeolites, to radicals and macroradicals formed by ionizing radiation in zeolites, and in organic hosts such as urea and PHTP . Radicals as probes have also been produced by photolysis .…”

Section: Introductionmentioning

confidence: 99%

Dynamics of Alkoxy−Oligothiophene Ground and Excited States in Nanochannels

et al. 2004

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Two oligothiophenes, 4,4'-dipentoxy-2,2'-dithiophene and 4,4"-dipentoxy-2,2':5',2":5",2' ''-tetrathiophene, have been included in the nanochannels of the autoassembling host TPP (tris-o-phenylenedioxycyclotriphosphazene). The effect of the confinement on the structure and properties of the two dyes, as conformational arrangements, dynamics, and photophysical behavior, was addressed by the combination of high spinning speed solid-state NMR and time-resolved EPR spectroscopy. We compared the conformations of the dyes in their ground and photoexcited triplet states and described in detail the dynamics of the supramolecular adducts from 4 K to room temperature. Above 200 K surprisingly fast spinning rates of the dithiophene core were discovered, while the side chains show far slower reorientation motion, being in bulky gauche-rich conformations. These lateral plugs keep the planar core as appended in the space like a nanoscale gyroscope, allowing a reorientation in the motion regime of liquids and a long triplet lifetime at unusually high temperature. The nuclear magnetic properties of the guest dyes are also largely affected by the aromatic rings of the neighboring host, imparting an impressive magnetic susceptibility effect (2 ppm proton shift). The high mobility is due to the formation of a nanocage in a channel where aliphatic and aromatic functions isolate the thiophene moieties. Instead, two conformers of the tetrathiophene twisted on the central bond are stabilized by interaction with the host. They interconvert fast enough to be averaged in the NMR time scale.

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Section: Introductionmentioning

confidence: 99%

Dynamics of Alkoxy−Oligothiophene Ground and Excited States in Nanochannels

et al. 2004

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“…1 Moreover, the supramolecular organization and the topological constraints give rise to a different conformational and motional behavior of the guests. [2][3][4] In this paper we report a study on the photoexcited triplets of three nitro substituted diphenylpolyenes in IC and in glassy and polymeric matrices.…”

Section: Introductionmentioning

confidence: 99%

Photoexcited triplets of nitrodiphenylpolyenes hosted in channel cavities. A time resolved EPR study

Barbon

Bortolus

Brustolon

et al. 2004

Phys. Chem. Chem. Phys.

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The photoexcited triplet states of the three nitro substituted diphenylpolyenes 4-nitrostilbene, 4-nitrodiphenylbutadiene and 4,4'-dinitrodiphenylbutadiene included in nanostructured channel-like cavities of a PHTP-based inclusion compound have been investigated by time-resolved electron paramagnetic resonance. The inclusion compounds were synthesized by using as host dihydrotriphenylene partially hydrogenated. The same dyes have been studied also in disordered solid matrices. The triplet states produced in the inclusion compounds originate only from the ground state trans conformer, since the constraint of the host channel prevents the trans-cis photoisomerization. The simulation of all spectra in disordered matrices shows the presence of the same triplet from the trans isomer as in inclusion compounds, but also of another state with the same ZFS parameters and different spin polarization. This derives from the cis isomer through a photophysical path to the cis triplet relaxing therefore conformationally to the trans triplet. For the diphenylpolyene derivatives the effect of irradiation at two wavelengths has been studied, giving further support to this interpretation of the spectra. Comparison of the experimental ZFS parameters with the calculated ones and with those of the corresponding unsubstituted compounds shows that the nitro groups are tilted out of the pi-system plane. The tilting angle is different in the inclusion compounds with respect to the disordered matrices as a consequence of the head-to-tail interactions between nitro groups in neighbour molecules packed in the channels

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“…This has been shown by studying a series of UIC in which the guest species is a mixture with different concentrations of 10-NDO and nonadecane. 8 The radical is formed on the ketone molecules only, and it is found that the EPR linewidths are smaller and the radical motion faster when the composition of the guest mixture is richer in nonadecane. All the other experimental settings being the same, this result implies that the motion of the 10-NDO radical is affected by the type of molecules occupying the adjacent channels.…”

Section: Methodsmentioning

confidence: 99%

“…In particular, we have recently studied UIC with several types of functionalized alkanes as guest molecules by EPR and ENDOR spectroscopy. [5][6][7][8] Single crystals of the desired compound were produced and then γ-irradiated. Stable radicals are produced only on the guest molecules by cleavage of a C-H bond near the functional group.…”

Section: Introductionmentioning

confidence: 99%