Solvatochromic behavior

The solvatochromic behavior of these dyes in solution can be explained by the comparison of their permanent dipole moments. If the excited state exhibits a larger dipole moment (pii) than the ground state (/i0), it is preferentially stabilized by the more polar solvent, and the energy between these two states decreases, that is, the absorption and emission spectra both shift to the red region. 

The solvatochromic behavior of the closely related iron(0) complexes Fe(CO)3(diimine) is mentioned under lower oxidation states (Section 5.4.3.5.6). 

Owing to the presence of the amine and cyanide ligands, known to give rise to specific donor-acceptor interaction with solvents [126-130], an interesting solvatochromic behavior is observed for these species. For complex 1 the spectral changes are dominated by amine interactions with the solvents as shown by the linear correlation of the solvent donor number [131] with the IT band maxima and with the half-wave potential of the ruthenium amine moiety. 

If we compare AX values (AX - XDMSO - Xj0iuene) for the four dyes under study we get 35 nm (1428 cm 1), and 27 nm (1269 cm 1), for the nitro, and methylsulfonyl azobenzene derivatives, respectively, and 22 nm (1077 cm 1), and 7 nm (457 cm1), for the nitro, and methylsulfonyl stilbene derivatives, respectively. Further examination reveals that the difference in AX between the two stilbene derivatives is 15 nm (620 cm 1), while that in the case of the azobenzene derivatives is 8 nm (159 cm1). Thus, two interesting conclusions can be drawn from this data a) the bathochromic shift is not only a function of the donor and acceptor groups, but also of the intermediate -system between them and (b) while the measured hyperpolarizability coefficients for the stilbene and azobenzene sulfonyl derivatives are very similar (see below), their solvatochromism behavior is different, and therefore solvatochromism is not an accurate prediction of p. 

Mixtures of C02 and methanol were selected for the initial investigation of the solvatochromic behavior in supercritical fluid systems. This combination is of interest as it combines the low critical temperature and pressure of carbon dioxide with a polar, less volatile modifier. This system exhibits relatively simple Type I phase behavior and several groups have published measurements of mixture critical points (19-21). At intermediate compositions the critical pressure for this fluid is much higher than that of either pure C02 or pure methanol, reaching a maximum of approximately 2400 psi (20). 

Fig. 9. Solvatochromic behavior of didodecyl-PPE 12c upon addition of methanol.

S.-R. Keum and K.-W. Lee, Unusual solvatochromic behavior of the open-chain merocyanine forms of 5-chlorinated l,3,3-spiro(2/7-l-benzo-2,2 -indoline) derivatives, Bull. Korean Chem. Soc., 14, 16-18 (1993). 

Compound 12, incorporating two heterocyclic nuclei, is very polarizable and shows a large solvatochromic behavior.9 A polar solvent shifts the equilibrium toward the opened form as shown in Table 2.7. Nuclear magnetic resonance (NMR) experiments (400 MHz 1H) showed that the open forms of merocyanines are transoid toward the azomethine bridge. The delocalized electronic structure tends to become more quinoidal with decreasing polarity of the medium.9... 

From Tables 4.16 and 4.17 we can see that the solvent polarity has different effects on fulgide 62 and its colored form (63). For fulgide 62, solvents had little effect on the absorption maxima. However, a strong solvatochromic behavior was observed for the colored forms (63). More detailed absorption spectra data for 62 and 63 in various organic solvents are listed in Table 4.18. The polarity of the solvents was represented by the Dimroth scale t(30).88... 

It was shown that the spectroscopic detection is influenced by the varying optical properties of the solvent and by the solvatochromic behavior of the nitroaromatic compounds at different CO2 densities. These specific effects have to be known for a accurate spectroscopic identification and quantification of analytes dissolved in sub- and supercritical carbon dioxide... 

The UV absorption and fluorescence properties of 9-(9 -acridyl)carbazole have been investigated in 50 different solvents, and only representative examples are reported <1998EJ01697>. The carbazole unit serves as an electron donor and analysis of the solvatochromic behavior revealed that twisted intramolecular charge transfer emission prevails only in more polar solvents. 

Combining the idea of solvent-induced changes in molecular structure with the concept of a solvent continuum around the solvatochromic molecule, a micro-structural model of solvatochromism has been developed by Dahne et al., which reproduces, qualitatively correctly and quantitatively satisfactorily, the solvatochromic behavior of simple merocyanine dyes [95b], The results obtained with this model for 5-(dimethylamino)penta-2,4-dienal are in good agreement with the solvent-dependent experimental data such as transition energies, oscillator strengths, r-electron densities, and r-bond energies [95b] cf. also [326, 327],... 

A special property of these luminescent carbonyl diimine complexes is their solvatochromic behavior. The MLCT absorption bands exhibit a noticeable red shift when the polarity of the solvents decreases (negative solvatochromism). For example, the MLCT transition of [Re(CO)3(bpy)Cl] occurred at 370 and 400 nm in CH3CN and benzene respectively. Similar solvatochromism was also observed for the charge-transfer bands of other carbonyl complexes... 

Aminophenoxazone dyes were studied by Otsuki and Taguchi94 with respect to their solvatochromic behavior in non-hydrogen-bonding polar solvents. The absorption spectra of 7-A,A-dimethylamino-3-phenoxazone (77), its 7-A,A-diethylamino analog and its 1-methyl analog were measured in several neat solvents and in aqueous dioxane solutions and the peak positions correlated linearly with the jt scale. The fluorescence emission peak, however, was not linear with jt. ... 

Dimroth and Reichardt devised a scale based on the solvatochromic behavior of the pyridinium-V-phenoxide betaine dye shown in Figure 1(a).5 The UV spectrum varies over several hundred nanometers according to the solvent in which it is dissolved. The wavenumber observed relates to T(30) or normalized f TN values. At one end of the TN scale is cyclohexane with a value of 0.006, and water lies at the other end with a value of 1.000. 

Several 2// -chromcnc derivatives exhibit photo-, thermo- or solvatochromic behavior in solution. Specific structural features of the substituted di-phcnylchro-menes CH1-CH4, the dimethyl chromenes CH5, and the spiro[fluorene-benzopyr-ans] SFB1 and SFB2 have been studied.75 77... 

In this contribution we review the connection between the nonlinear optical (NLO) response and the solvatochromic behavior of the important class of organic molecules, namely donor-acceptor -tr-conjugated compounds (D-tr-A). In these compounds, also called push-pull chromophores, an electron-donating group D is conjugated to an electron-acceptor substituent A through a system of the localized tr-bonds (Scheme 1). It is well established that such compounds exhibit the following properties [1-7] ... 

In the present contribution we will discuss the direction of the changes of the NLO response and the solvatochromic behavior as a function of solvent polarity of the D-tt-A chromophores. The best starting point for these considerations seems to be the simple two-state model for the first-order hyperpolarizability (/ ) [8]. To avoid the extreme complexity of the sum-over-states (SOS) expression [101], Oudar and Chemla proposed the relation between the dominant component of 13 along the molecular axis (let it be the x-axis) and the spectroscopic parameters of the low-lying CT transition [8]. The use of the two-level approximation in the static case (ru = 0.0) has lead to the following expression for the static component of the first-order hyperpolarizability tensor ... 

The electronic spectrum of (14) and its isomer (20) which both form highly conductive complexes with TCNQ and analogous acceptors have been reported <90BCJ244l>. The solvatochromic behavior of the ditellurides (1), (21), and (22) has also been discussed <93JA885>. 

The solvatochromic behavior of the 3[da, n ] (3MMLCT) emissions of 7b(C104)2 and llb(C104)2 has also been studied (Table 2). The emission ener-... 

Yonker, C. R., and R. D. Smith. 1988. Solvatochromic behavior of binary supercritical fluids The carbon dioxide/2-propanol system. J. Phys. Chem. 92 2374-2378. 

While in solution only a broad band centered at 385 nm is observed, thin films of these materials are distinctly yellow with a sharp absorption at Amax of 435 nm. The absorption behavior is mostly independent of the alkyl substituent. To understand the nature of the transition from solution to the solid state, the solvatochromic behavior of PPEs was examined. Solvatochromic behavior in conjugated polymers has long been known and has been documented by Rughooputh and Wudl"° for polythiophenes. In the case of the dialkyl-PPEs 3 addition of a nonsolvent (methanol) to a chloroform solution of 3 leads to the development of a new and very sharp band centered at 435 nm, which corresponds to the absorption observed in the solid state. In addition, the transition observed in chloroform at 385 nm is shifted to 400 nm and vibronic structure develops. 

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