Boron chromophores

NLO materials (16 and 17) (Fig. 13) have been obtained from polyurethanes by the incorporation of sidechains with boron chromophores.37 The dihydroxy ligand of an azobenzene ligand containing a dimesityl boron acceptor was reacted in a polycondensation fashion with the diisocyanate groups of the polyurethanes to yield the desired polymers. Halogen displacement and transmetallation reactions have been utilized in the development of extended ir-conjugated systems of tri-9-anthrylborane with dendritic structures.38 In one (18) (Fig. 14) of the novel compounds, three identical... 

Figure 13 Boron chromophore-containing polyurethanes (16 and 17) for NLO applications. (Adapted from ref. 37.)... 

Even the concept of molecular switch is an important topic from a variety of perspectives ranging from the modelling of biological processes to the design of devices for molecular electronics. The idea of switching directly the NLO properties has recently been envisioned [151]. Lamere et al. have reported on the synthesis and characterization of a boronate chromophore built up from two push-pull NLO sub-units in a quasi-free rotation around a chemical axis. They discussed on the possibility to use such a system as a molecular NLO switch induced by an electric field [152]. 

C. Branger, M. Lequan, R. M. Lequan, M. Large, F. Kajzar, Polyurethanes containing boron chromophores as... 

Fig. 42. A series of boronic acids 159-166 with chromophoric groups has been evaluated with respect to its capacity to selectively bind d-glucose or other saccharides...

In 159 and 163-166 the tertiary amine function is coordinated to the boron atom and transmits the electronic change due to the ester formation to the chromophore. In 160-162 the boron atom is directly connected to the chromophore. After the complexation of the saccharide, the change of the charge transfer, e.g., for 159 [249-251], or the fluorescence bands, e.g., for 160-166 [252-255], can be measured and interpreted. The most selective binding of n-glucose has been achieved with host 164 that forms a 1 1 complex with a macrocyclic structure (Scheme 1). 

Compounds 167-171 outlined in Fig. 43 form another series of diboronic acids that form complexes with mono- and disaccharides. In these cases the asymmetrical immobilization of chromophoric functional groups, e.g., aromatic rings in 167-170 or Fe -complexation with the related boronate 171, can be analyzed by circular dichroism measurements [256-262]. 

In order to minimize the fast electron-hole recombination, Calzolari et al. [50] attached a donor-acceptor boronic acid spacer between the anthocyanins and a gold electrode, and the same molecule between the dye and a P-cydodextrin which is able to bind I3 dissolved in the electrolyte near the chromophore. In that configuration, the device shows an increase in the quantum yield of the photocurrent from a negligible value to 1.75%. Such studies were not repeated on Ti02 layers. 

In an effort to prepare bidentate boranes as colorimetric anion sensors, the incorporation of chromophoric boron moieties has also received attention. Reaction of lO-bromo-9-thia-lO-boranthracene 33 with dimesityl-1,8-naphthalenediylborate 26 affords diborane 34 (Scheme 14). This bright yellow diborane is soluble in chloroform, THF and pyridine. It has been fully characterized but its X-ray crystal structure could not be determined experimentally. Its structure was computationally optimized using DFT methods (B3LYP, 6-31 + G for the boron and sulfur... 

Porphyrins are chromophores, occurring in diverse molecules, such as hemoglobin and chlorophyll. They have a propensity to accumulate in tumors (81). Boronated porphyrins or their derivatives have great potential as boron carriers in boron neutron capture therapy (82). 

The double nitrates Mg3M2(N03)12, 24 H20 can be recrystallized in strong nitric acid and serve to separate the lighter lanthanides M = La, Pr, Nd and Sm (where Ce has been removed after oxidation to the quadrivalent state). Judd noted 109) that the fine-structure of the absorption band belonging to each /-level of M(III) was so peculiar that it looked as if the chromophore was icosahedral with N = 12 (which is almost unheard about, outside boron chemistry). The crystal structure 110) of the cubic crystals confirmed entirely Judd s proposal, it is indeed [Mg(OH2)6]3 ... 

The synthesis [25, 26] began with 7-bromo-l-tetralone (7), available in multigram quantity in three steps from succinic anhydride and bromobenzene [27, 28] (Scheme 1). Treatment of 7 with an aromatic aldehyde and base produces the corresponding benzylidene (e.g., 8) which couples with 7 in boron trifluoride etherate to form a pyrylium salt. This pyrylium salt is not isolated but treated with ammonia to afford functionalized spacer 9. As seen in Scheme 1, the attachment of anthracene [29] or acridine chromophores occurs in a single step. Alternatively, stepwise attachment of the aromatic chromophores allows construction of molecular tweezers 12 and 13 carrying different chromophores. With respect to efficiency, tweezers 10 and 11 are synthesized in six steps from inexpensive starting materials with overall yields of 11% and 14%, respectively. 

Figure 10. A nine-chromophore species made of eight peripheral boron dipyrrole pigments and one central porphyrin, acting as the energy sink [31a].

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