Solvatochromic properties of long alkyl chain π* indicators: comparison of N,N‐dialkyl‐4‐nitroanilines and alkyl 4‐nitrophenyl ethers

Abstract

Hydrophobic forms of the N,N-dialkyl-4-nitroaniline (DNAP) ( p-O 2 NC 6 H 4 NR 2 ) (1a-f) and alkyl-4nitrophenyl ether ( p-O 2 NC 6 H 4 OR) (2a-c) solvatochromic p à indicators have been characterized and compared with respect to: (a) solvatochromic bandshape, (b) sensitivity expressed as Ss, (dv max /dp à ), and (c) trends in Às with increasing length of alkyl chain(s) on the probe molecule. -Octyl 4-nitrophenyl ether ( p-O 2 NC 6 H 4 OC 8 H 17 ) (2b) and -decyl 4-nitrophenyl ether ( p-O 2 N C 6 H 4 OC 10 H 21 ) (2c) were synthesized and their solvatochromic UV/Vis absorption bands were found to maintain a Gausso-Lorentzian bandshape for the indicators in non-polar and alkyl substituted aromatic solvents, for example, hexane(s) and mesitylene. Corresponding absorption bands for 1a-f display increasing deviation from a Gausso-Lorentzian shape in the same solvents as the alkyl chains on the indicator are increased in length all the way to C 10 and C 12 , for example, N,N-didecyl-4-nitroaniline ( p-O 2 NC 6 H 4 N (C 10 H 21 ) 2 ) and N,N-didodecyl-4-nitroaniline ( p-O 2 NC 6 H 4 N (C 12 H 25 ) 2 ) (1d-f). A plot of Às versus C n follows a 1st order decay for the DNAP indicators but is linear for the alkyl 4-nitrophenyl ethers. A discussion of how the long alkyl chains on the two types of indicators affect the orientation and overlap of n and p à orbitals, and resulting solvatochromic bands is presented. For DNAP, overextending the alkyl chains to obtain greater hydrophobic character may cause the alkane component to dominate solute-solvation processes at the expense of the probe's fundamental solvatochromic character. a Range of Chi-square ¼ 9.5  10 À6 to 4.0  10 À5 ; range of r 2 ¼ 0.9539 to 0.9886. b Range of Chi-square ¼ 9.3  10 À6 to 4.5  10 À5 ; range of r 2 ¼ 0.9489 to 0.9893. c Range of Chi-square ¼ 7.10  10 À6 to 5.0  10 À5 ; range of r 2 ¼ 0.9037 to 0.9923. d Range of Chi-square ¼ 7.15  10 À6 to 6.0  10 À5 ; Range of r 2 ¼ 0.9152 to 0.9919. e Values are for cyclohexane. f Values are for the cyclic ether dioxane. Figure 4. Solvatochromic (UV/Vis) absorption bands of 2a (left) and 2c (right) in hexane(s)

Solvatochromic Measurement of KAT Parameters and Modeling Preferential Solvation in Green Potential Binary Mixtures of N-Formylmorpholine with Water, Alcohols, and Ethyl Acetate

“…All of NFM + alcohols mixtures show the synergy in hydrogen bond basicity. Synergism occurs when two pure solvents form hydrogen-bonding complexes that show different polarity compared to the pure solvents. − The negative deviation of β reveals that hydrogen-bonding complexes formed by interactions between NFM and alcohols have lower β than two pure solvents.…”

“…However, DMPNA shows greater polarity sensitivity as well as less change in the spectral band shape. In addition, its spectral band does not show overlapping with solvent absorption studied in this work . In practice, eq is used to determine π* from υ̅ DMPNA …”

“…In addition, its spectral band does not show overlapping with solvent absorption studied in this work. 18 In practice, eq 2 is used to determine π* from υ ̅ DMPNA . 19 π ν * = − ̅ 28.…”