Tuning octopolar NLO chromophores: synthesis and spectroscopic characterization of persubstituted 1,3,5-tris(ethynylphenyl)benzenes.

The synthesis of a series of octopolar 1,3,5-tris(ethynylphenyl)benzenes via Sonogashira coupling is described, varying the substituents on both the central benzene core as well as the acetylenic periphery. In particular, systems bearing an electron-rich core and an electron-poor periphery are obtained that display advanced optical properties. The linear (by UV-vis and fluorescence spectroscopy) and second-order nonlinear optical properties are studied, the latter by hyper-Rayleigh scattering (HRS) (Hendrickx, E.; Clays, K.; Persoons, A. Acc. Chem. Res. 1998, 31, 675-683). The influence of different core and periphery substitution is revealed by the optical properties and confirms the possibility of fine-tuning those. Because of the presence of (one-photon) fluorescence for all compounds, femtosecond hyper-Rayleigh scattering has been applied (Olbrechts, G.; Strobbe, R.; Clays, K.; Persoons, A. Rev. Sci. Instrum. 1998, 69, 2233-2241). The implementation of the deconvolution in the frequency domain allows for a demodulation and a phase shift between immediate (nonlinear) scattering and time-delayed (multiphoton) fluorescence for high modulation frequencies (Wostyn, K.; Binnemans, K.; Clays, K.; Persoons, A. Rev. Sci. Instrum. 2001, 72, 3215-3220). In accordance with the linear optical properties, the second-order NLO properties can also be tuned by varying the core and peripheric substitutents.