Syntheses of Sterically Hindered Zwitterionic Pyridinium Phenolates as Model Compounds in Nonlinear Optics

Abstract

Pyridinium phenolates possess a dissymmetric delocalised π-electron system providing a huge quadratic nonlinearity. They are a promising class of molecules for applications in photoelectronics and photonics. Semiempirical calculations indicate that the interplanar angle between the two aromatic rings leads to enhancement in the NLO properties of these compounds. The confirmation of this feature may be provided by the study of a new series of sterically hindered pyridinium phenolates 2a-e bearing two tert-butyl substituents

Electron Transfer between Hydrogen‐Bonded Pyridylphenols and a Photoexcited Rhenium(I) Complex

“…The protected phenols ( 2 and 4 ) are reacted with pyridine molecule 5 (which is accessible in one step from 2‐picoline and diisopropyl ketone) by using a palladium catalyst 8. The coupling products ( 6 and 8 ) are deprotected with aqueous HBr (in the case of 6 )9 or ethanethiol (in the case of 8 )10 to obtain the final pyridylphenols ( 7 , PhOH‐CH 2 ‐py and 9 , t Bu 2 PhOH‐CH 2 ‐py).…”

“…On subjecting molecule 8 to the same methoxyl‐deprotection reaction with aqueous HBr as described above for molecule 6 , not only the methoxyl group but also the tert ‐butyl substituents of molecule 8 were cleaved off and the reaction afforded molecule 7 . It was therefore necessary to apply the following procedure to obtain molecule 9 10. Ethanethiol (0.69 g, 11.2 mmol) was added dropwise to a suspension of NaH (60 % in mineral oil, 0.31 g, 12.8 mmol) in dry N , N ‐dimethylformamide under N 2 atmosphere.…”

A 13C NMR Study of pyridinium phenoxide series with increasing sterical hindrance reveals the dramatic influence of torsion on their structure

“…The synthesis of all compounds were already published. 8,9 Procedure for deuteration studies on 1a-d: 2 mL of a solution of 1a-d (0.9 x 10 -2 M) and KOH (10 -1 M) was prepared. 1 H NMR spectrum of this solution is recorded after 45 s and then every 10 min over 5 h.…”

“…6,7 We have recently synthesized two series of five pyridinium phenoxides 1a-e and 2a-e (scheme 1) with different torsion angles between the two phenyl rings. 8,9 This was achieved by increasing the steric hindrance through the introduction -at the ortho, ortho' position of the intercyclic bond -of alkyl groups R1, R2 (at meta position of the phenolate functionality for 1a-e) or R3, R4 (at meta position of the pyridinium ring for 2a-e) with different sizes.…”

Concerning restricted rotations in pyridinyl anisoles and pyridinyl phenols bearing saturated handles, and their solid state structures

“…11 These drawbacks may be avoided by introducing bulky groups at the ortho position of the phenolate. [4][5][6][7][8][9][10][11][12] In this context, we have recently synthesised pyridinium phenolates bearing saturated handles of various lengths (compounds 1a-d, Scheme 1). 13 A moderate twist angle was introduced by anchoring two methyl groups at the meta position of the pyridine ring to retain reasonable NLO responses.…”