Solvatochromism chromophores

Finally, Harper has investigated the use of negative solvatochromic chromophores. This method involves the use of chromophores that are predominantly charge separated in the ground state. Chromophores of this type exhibit negative hyperpolarizabilities, since polarization occurs from acceptor to donor of conventional chromophores. Harper has prepared a model system that is composed of two molecules of similar donor and acceptor and of the same conjugation length, shown below. 

Molecular encapsulation in dendritic and highly branched polymers has received increasing attention recently. It was shown for dendrimers that the site isolation of a fimaional core unit in a dendritic scaffold is of great interest with respect to optical properties, catalysis, and other future applications. Detailed studies on dendrimers have revealed that at some critical dendrimer generation, the core is encapsulated by the sterically aowded and densely packed highly branched architecture. Within this context, Frechet et al introduced l-(N,N-dimethylamino)-4-nitrobenzene as a solvatochromic chromophore at the focal point of a poly(benzyl ether) dendrimer. In other works, manganese and zinc porphyrins... 

Solvatochromic probes have been used for a variety of applications like the study polarity of pure and mixed solvents [99], and the retention behavior in reverse-phase liquid chromatography [100] among other applications. Frechet et al. used 4-(N-methylamino)-l-nitrobenzene (p-MANB), as the chromophore, to probe the microenvironment of polyaromatic ether based dendrimers [101]. 

Webber NM, Meech SR (2007) Electronic spectroscopy and solvatochromism in the chromophore of GFP and the Y66F mutant. Photochem Photobiol Sci 6 976-981... 

Dong J, Solntsev KM, Tolbert LM (2006) Solvatochromism of the green fluorescence protein chromophore and its derivatives. J Am Chem Soc 128 12038-12039... 

The details of how nitroaromatic explosive molecules interact with the chromo-phores in the polymer matrix requires further study. Initial observations suggest that because nitroaromatic explosive molecules are highly electron-deficient, that chro-mophores have an electron-rich donor and bridge, and that both nitroaromatic explosives and chromophores are highly polar, explosive molecules and chromo-phores have a strong tendency to interact with each other. The interaction between explosives and the polymer takes place in two steps. In the initial step nitroaromatic explosive molecules create a more polar environment around the chromophores. The increased polar environment produces a solvatochromic red-shift of the... 

The optical spectra of the stilbene and azobenzene derivatives were studied in different solvents to establish the solvatochromic shifts of the new sulfonyl-containing chromophores, and to compare them to those found for the nitro analogues. Figure 3 shows the spectra in toluene and in DMF of 4-dibutylamino-4 -nitrostilbene, and of 4-dibutylamino-4 -methylsulfonylstilbene, and Figure 4 shows the spectra in the same solvents, but of 4-dibutylamino-4 -nitroazobenzene, and 4-dibutylamino-4 -methylsulfonylazobenzene. Table II summarizes the results. 

Another nonreactive route to the characterization of solvent polarity is the study of the optical absorption and emission spectra of chromophores [188]. These spectra are sensitive to the molecular environment, and because different solvatochromic probes may have different capacities for specific interactions, it is possible to characterize the solvent environment in detail and to construct LFERs analogous to those described above. Studies of the spectra of solvatochromic probes in ionic liquids have in general been consistent with the results of partitioning studies described above [8-10, 69, 70, 198-200], though we will discuss one observed anomaly below [198]. 

Nicolet and Laurence11 studied four phenyl — NALk2 probes not mentioned previously nor included in Table 1 iV,iV-diethyl-3,4-dinitroaniline (38), 4-iV,iV-diethylaminobenzal-dehyde (39), V,lV-dimethylaminobenzonitrile (40) and methyl 4-iV,iV-dimethylamino-benzoate (41), the former two at several temperatures from 0 to 105 °C, the latter two only at 25 °C. The last three probes as well as 6, 42 and 43 mentioned in Table 1 show that the nitro or nitroso chromophore group is not necessary for obtaining useful solvatochromic probes. 

Under this heading are collected solvatochromic probes which have an amino group attached to a phenyl ring that in turn is bonded by more than one bond to other moieties (Schemes 2 and 3). All these groups are generally further substituted in order to produce chromophores that have a wide solvatochromic amplitude. 

Estimation of A/rol from the solvatochromic slope is roughly possible applying the Onsager model [59, 334—336], Large changes of A/% can be accomplished by introduction of appropriate donor and acceptor groups at the re-skeleton of the chromophore. Extension of the re-system results additionally in an increase of Ap01. A summary of solvatochromic data is compiled for dipolar compounds elsewhere [334, 335, 337],... 

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