N-Alkyl-p-nitroanilines: impact of alkyl chain length on crystal structures and optical SHG

Abstract

N-Alkyl-p-nitroanilines from the propyl to the octyl derivative are synthesised and characterised. Powder SHG studies show that the butyl derivative alone is active, in agreement with earlier observations. Crystal structures of the propyl, butyl and pentyl derivatives are determined; the propyl and pentyl derivatives belong to the centrosymmetric space groups P1 and P21/1v\c respectively and the butyl derivative to the noncentrosymmetric P212121 space group. Detailed analysis of these structures provides insight into the critical role of the alkyl chain length in the formation of centrosymmetric or noncentrosymmetric crystal lattices. The utility of alkyl chain length as a crystal design element for quadratic NLO materials is noted.