Synthesis and Nonlinear Optical Properties of End-Group Modified Aromatic Esters As Chained Chromophores

We synthesized aromatic ester derivatives with some electron accepting groups at molecular ends as new class of nonlinear optical (NLO) active chromophores (ArESn-X, n = 2, 3, X = CN, CF₃, NO₂, DCV). Some second-order NLO properties for poled polymer films consisting of poly(methyl methacrylate) (PMMA) doped with 10 wt.-% ArESn-X(ArESn-X/PMMA) were investigated. UV/vis spectra of these polymer films have cutoff wavelengths (lambda_co) of about 300�`380 nm, which are much shorter than in the case of p-nitroaniline (pNA) (lambda_co = ca. 450 nm) as a typical strong donor-acceptor (D-A) molecule. In addition, some of these polymer films exhibited larger second-order nonlinear coefficient (d₃₃) values than PMMA film doped with 10 wt.-% pNA (pNA/PMMA) (2.8�~10^-9 esu). Namely, ArES3-CN (d₃₃ = 3.1�~10^-9 esu, 10 wt.-% in PMMA), ArES3-NO₂ (3.0�~10^-9 esu, 10 wt.-% in PMMA) and ArES2-DCV(4.0�~10^-9 esu, 10 wt.-% in PMMA) showed not only excellent second-order NLO activity but also excellent transparency in the visible region (lambda_co = 304 nm (ArES3-CN), 340 nm (ArES3-NO₂) and 370 nm (ArES2-DCV), respectively). Consequently, these compounds are believed to be promising chromophores for second-order nonlinear optics.

Fig. 1. Concept of end-group modified Chained Chromophore.