Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Stilbene chromophores

Bazan and co-workers [93] coupled four branches of stilbene chromophores to a central C atom, leading to tetrastilbenylmethane [C(STB)4, 46a] tetrakis (4-ferf-butylstyryIstiIbenyljmethane [C(f-BuSSB)4, 46b], and the higher homolo-gue tetrakis 4-[4 -(4"-terf-butyl-styryl)styryl]stilbenyl methane [C(4R—f-Bu)4, 46c]. For 46b, Tg is 190°C, and for 46c it is as high as 230°C. Tetrakis(4,4 -2,2-diphenyl-vinyl)-l,l -biphenyl]methane [C(DPVBi)4, 47a] and the cyano derivative 47b exhibit the glass transition at 142 and 174°C, respectively. Similar compounds to 46a and 46b have also been synthesized with silicon and adaman-tane as the tetrahedral center. [Pg.120]

Structurally these compounds combine a eight-coordinate tetracarboxylate chelating site with stilbene chromophores. Of the six dyes proposed in Ref. 121 only Indo-1 leads to a short-wavelength fluorescence shift when bound to Ca2+. It is also the probe with the smallest D-A interactions as revealed by the shortest wavelength of fluorescence of the free ligand. As a consequence, the decrease of the electron density of the nitrogen binding site is not sufficient to break completely the interaction with Ca2+ in the excited state and the spectrum is considerably blueshifted. [Pg.137]

Photodimerization of the stilbene chromophore in small or medium ring systems is highly dependent upon the ring size. Indeno[2,l-a]indene (5) yields a 1 2 mixture of head-to-head head-to-tail dimers 28 and 29 (eq. 12) upon irradiation in... [Pg.179]

The reaction of t-1 with dimethyl fumarate is proposed to occur via the weakly fluorescent singlet exciplex intermediate (76). Increasing the solvent polarity results in a decrease in both the exciplex fluorescence intensity and the cycloaddition quantum yield, presumably due to radical-ion pair formation. The low efficiency of cycloaddition from c and the absence of triplet cycloaddition indicate that a planar stilbene chromophore is necessary for exciplex formation (see also Sections V-B and C). [Pg.189]

M s in DMSO-water in the presence and absence of amylose. Thus quenching is reduced about 30-fold for iodide by amylose incorporation of the stilbene chromophore. While it is somewhat uncertain as to what precisely the nature of the quenching of stilbene by iodide is, it is reasonable to assume that the reduced quenching constants imply a more difficult approach of the iodide ion to the complexed stilbene than to the free. We are currently exploring many aspects of reactivity of amylose-incorporated chromophores. We find for example that amylose is able to extract totally insoluble hydrophobic stilbene molecules into water and we are presently trying to obtain crystal structural data on the complex molecule. The dynamics of complex formation and dissociation are currently under investigation. [Pg.187]

The sterically overcrowded alkenes shown in Scheme 6 have been exploited in our group since, from the perspective of molecular switches design, they combine a number of attractive structural features. Steric interactions between the groups attached to the central olefmic bond force these molecules to adapt a non-planar helical shape. The chirality of these so-called inherently dissymmetric alkenes 3, is therefore the result of distortion of the entire molecular structure. Beside the heli-cene-like geometry, both a cis- and a trans-stilbene chromophore are present in the same molecule. [Pg.132]

Fig. 11.19 Structures and data showing how (5max (2PF method) for dendritic-type bis(diarylamino)stilbene chromophores increase in a superlinear fashion with the... Fig. 11.19 Structures and data showing how (5max (2PF method) for dendritic-type bis(diarylamino)stilbene chromophores increase in a superlinear fashion with the...
The light-induced reversible trans-cis photoisomerisation of franv-stilbene molecule in condensed media includes at least four macroscopic stages excitation of the stilbene chromophore, radiative deactivation of the excited state with the rate constant kr, medium relaxation around the excited stilbene molecule with the rate constant km (to provide space for torsional distortion during the photoisomerisation process) and eventually, twisting transition with the rate constant kt c. [Pg.11]

Photostimulated expansions observed for small elongation in polyamide film containing stilbene chromophores in the polymer backbone may be explained by the thermal effect [31]. The solution viscosity of this polymer decreased upon photostimulated trans-cis isomerization, while the film showed a decrease in force. In this system, the photoheating effect dominates the photochemical one. [Pg.47]

From a similar point of view Osada and Katsumura21 examined the photomechanical energy conversion of a polyamide containing a stilbene chromophore in the backbone (XVIII) ... [Pg.41]

Figure 5.9 Star-shaped compounds or dendrimers having ( )-stilbene chromophores linked by (branched) spacers Sp to the core [38]. (Reproduced with permissions from Elsevier.)... Figure 5.9 Star-shaped compounds or dendrimers having ( )-stilbene chromophores linked by (branched) spacers Sp to the core [38]. (Reproduced with permissions from Elsevier.)...

See other pages where Stilbene chromophores is mentioned: [Pg.116]    [Pg.259]    [Pg.154]    [Pg.171]    [Pg.174]    [Pg.92]    [Pg.171]    [Pg.174]    [Pg.177]    [Pg.177]    [Pg.179]    [Pg.181]    [Pg.182]    [Pg.184]    [Pg.186]    [Pg.187]    [Pg.193]    [Pg.159]    [Pg.160]    [Pg.264]    [Pg.310]    [Pg.166]    [Pg.10]    [Pg.23]    [Pg.64]    [Pg.145]    [Pg.326]    [Pg.342]    [Pg.77]    [Pg.246]    [Pg.87]    [Pg.129]    [Pg.130]    [Pg.147]    [Pg.162]   
See also in sourсe #XX -- [ Pg.158 , Pg.159 ]




SEARCH



© 2024 chempedia.info