Synthesis and Solvatochromic Behavior of Zwitterionic Donor–Bridge–Acceptor Systems with Oligo(p-phenylene) Spacers

Abstract

Oligo(p-phenylene)s with a donor phenol group and an acceptor pyridinium moiety separated by one and two p-phenylene units were synthesized by the linear iterative Suzuki–Miyaura coupling method using aryl nonaflates as effective coupling reagents. Zwitterionic forms of these push–pull molecules were generated upon deprotonation of the phenol leading to large redshifts in absorbance maxima. UV-vis absorbance studies also revealed strong dependence of the band position on solvent polarity: a smooth bathochromic shift can be observed with the decrease of the solvent polarity. The molecule with one p-phenylene bridging unit showed the strongest solvatochromic characteristics in the series, spanning the range of 167 nm while moving from polar water to less polar N,N-dimethylformamide. The magnitude of this shift was close to Reichardt's dye — one of the most solvatochromic organic dyes known.

Planar in Brooker's mode and twisted in Reichardt's mode: defying the steric forces in biphenyl types of zwitterionic systems through metameric resonance stabilizations

“…1, where the steric constraints are prevalent in both cases (leaving no room for steric relaxations as the influential factor for conformational preferences). [18][19][20] Two zwitterionic molecules have pyridinium (+vely charged) as the acceptor and phenolate (Àvely charged) as the donor, but they differ with respect to the connectivity around the pyridinium N-atoms. [18][19][20] Here, they are represented as the Reichardt's type metamer 21 and Brooker's type metamer.…”

“…[18][19][20] Two zwitterionic molecules have pyridinium (+vely charged) as the acceptor and phenolate (Àvely charged) as the donor, but they differ with respect to the connectivity around the pyridinium N-atoms. [18][19][20] Here, they are represented as the Reichardt's type metamer 21 and Brooker's type metamer. 22 Quantum chemical investigations on the structures of these two metameric zwitterion molecules were carried out using various well-known methodologies, and the possible reasons for the exhibition of such differential behaviours are outlined in this contribution.…”

Amplifying the Negative Solvatochromism of Pyridinium Phenolates via Fluorene Conjugation

“…UV−vis spectroscopic analysis of fluorene series was performed and compared against Betaine 30. 13,19 With the alkyl chains on the fluorene unit, the solubility of the obtained species was significantly improved over previously reported OPPs. 19 Up to 10 solvents 19 we observed that deprotonated forms exist in protic solvents only for a short time and quickly undergo protonation.…”

“…The 1 H NMR spectra displayed significant upfield shifts of the most shielded aromatic signals compared to their protonated precursors, which were consistent with what were observed for previously reported OPPs. 19 Photophysical Properties. UV−vis spectroscopic analysis of fluorene series was performed and compared against Betaine 30.…”

“…Solvatochromic shifts of 356 and 300 nm were observed for Thiobetaine and Betaine 30, respectively, from 1,2-ethandiol to thiophene. 17 Our group has been studying another pyridinium phenolate dye (POMP), 18 and we reported a series of its oligophenylene derivatives 19 showing promising solvatochromic behavior (Figure 1). By extending the π system by one phenyl ring, we observed that the magnitude of solvatochromic shift for OPP(2)-O − was 167 nm between water and DMF.…”