A new synthesis of 1-phenylthio- and 1-alkylamino-4-nitrobuta-1,3-dienes

Abstract

A new synthesis of push-pull dienes such as 4-nitro-1-phenylthiopenta-1,3-diene 4 and 1-dialkylamino-4-nitropenta-1,3-diene 5, is described. The X-ray crystal analysis shows that 4-nitro-1-(pyrrolidin-1-yl)penta-1,3-diene 5a is essentially planar in an E,E-configuration with r(C–C)= 1.42(1)Å and r(CC)= 1.35(1) and 1.371(9)Å. Compounds 5 showed a large solvatochromic effects similar to that of merocyanine dyes. Molecule 5a exhibits second harmonic generation (SHG) activity whose efficiency is 2.5 times that of urea (determined by a powder method at 1064 nm). For 5a, the molecular nonlinearity µβ is estimated to be 1200 × 10^–48 esu which is calculated from the Pockel coefficient (r₃₃) determined by electrooptic measurements of poled polymers of 5a in poly(methyl methacrylate) at 1300 nm. This value is relatively large for such small conjugated molecules, where donors and acceptors are bridged by only 4π electron systems.