Solvatochromism in Pure Solvents: Effects of the Molecular Structure of the Probe

Abstract

The following solvatochromic probes were synthesized: 1-methyl-8-oxyquinolinium betaine (QB), sodium 1 -meth-yWoxyquinolinium betaine-5-sulphonate (QBS), and 1-methyl-3-oxypyridinium betaine (PB). Their solvatochromic behavior in 28 protic and aprotic solvents was investigated, and the data compared to those of 2,6-diphenyl-4-(2,4,6-triphenyl-l-pyridinio)-l-phenolate, (RB). Solvent polarity scales based on QB, QBS, and PB correlate linearly with the ET(30) scale of RB. The Taft-Kamlet-Abboud equation satisfactorily applies to the solvatochromic data of RB, QB, QBS and PB. The multiparameter regression coefficients (a) and (s) of the above mentioned equation show that the sensitivity of the probe to solvent dipolarity/polarizability, and hydrogen bond donation is clearly dependent on its molecular structure. This dependence was tested for a total of 26 probes of widely different structures. It is shown that this is a general behavior, i.e., log Iu I and 1s I are linearly dependent on the pK, and the dipole moment of the probe, respectively.

Differentiating Between Dipolarity and Polarizability Effects of Solvents Using the Solvatochromism of Barbiturate Dyes

“…Therefore, the use of solvatochromic probes has been established to measure the polarity effects of environments comprising not only well-behaved solvents and room-temperature ionic liquids, [3,4] but also inorganic surfaces, [5,6] biomolecules [7][8][9] and organized media. [10] In recent decades, the Kamlet-Taft approach [11] has successfully been applied to separate the influence of non-specific chemical interactions, including electrostatic effects (dipolarity/polarizability), from specific interactions, that is, hydrogen-bonding, which are related to the molecular structure of a compound. The commonly used simplified Kamlet-Taft equation applied to the UV/Vis absorption shift (ν max ) of a solute is given by Equation (1), [11] where ν max,0 is the solute property of a reference system, for example, a non-polar medium, α describes the HBD (hydrogen-bond donating) ability, β the HBA (hydrogen-bond accepting) ability, π* the dipolarity/polarizability of the solvents and a, b and s are solvent-independent correlation coefficients that indicate the contribution of the different solvent effects to the UV/Vis absorption shift.…”

Solvation in pure and mixed solvents: Some recent developments

“…Briefly, whereas the ability of solvents to form hydrogen bonds with the phenolate oxygen of RB is attenuated due to steric hindrance by the two ortho phenyl rings, the corresponding ability of WB is enhanced because of lower steric hindrance around the phenolate oxygen, and the additional ability of two ortho chlorine atoms to form hydrogen bonds [39]. Additionally, our solvatochromic data have indicated that lipophilicity of both solvent and probe are important to solvatochromism [36,38,[40][41][42]; there is no provision for the latter property in eq. 3.…”

“…3 [36][37][38][39][40][41][42][43][44][45]. Historically, the solvent polarity scales of RB and WB have been termed E T (30) and E T (33), respectively.…”

“…The data for QBS and PB were calculated from ref. [36]. b The abbreviations r 2 and (N) refer to the coefficient of multilinear correlation and number of solvents tested, respectively.…”

“…b The abbreviations r 2 and (N) refer to the coefficient of multilinear correlation and number of solvents tested, respectively. The relatively small value of (N) for QBS is dictated by its limited solubility in organic solvents [36]. Table 1 shows a clear trend: Probe/solvent interactions are dominated by a blend of nonspecific interactions, included in the dipolarity/polarizability term (π* S ), and specific interactions (in particular, hydrogen bonding to the probe phenolate oxygen) included in the α S term.…”