Nonlinear optical properties of benzofurobenzofurans

The geometric structure, dipole moment, mu, linear polarizability, alpha and first hyperpolarizability, beta, of symmetrically substituted amino- and cyanobenzofurobenzofurans and dihydrobenzofurobenzofurans have been calculated by ab initio coupled perturbed Hartree-Fock methods. Singlet electronic transition energies and excited state dipole moments have been calculated by the AM1 program. The benzofurobenzofuran derivatives are planar, while dihydrobenzofurobenzofuran derivatives have a V-shaped form, in agreement with experimental X-ray data. The molecular structure is rather unaffected by substitution. The linear polarizability is weakly sensitive to the substituent and substituent position, while beta value changes over about 1 order of magnitude. Although both series of compounds have relatively modest hyperpolarizability, reaching ca. 60% beta of para-nitroaniline, they have good properties for second harmonic generation devices: transparency in the visible spectral region, thermal stability and conformational rigidity.