title: 4H-Pyran-4-ylidenes: strong proaromatic donors for organic nonlinear optical chromophores.
abstract: Merocyanines where a polyenic spacer separates a 4H-pyran-4-ylidene moiety and different strong organic acceptors have been synthesized. According to NMR studies and X-ray diffraction data, these compounds have weakly alternated structures and remarkably zwitterionic ground states, with a partial aromatic character that is compared to those of other pyran derivatives. The proaromaticity of the 4H-pyran-4-ylidene donor lies behind the cyanine-like behavior and low (positive or negative) second-order optical nonlinearities of the shorter derivatives. On the other hand, lengthening the pi-spacer gives rise to rapidly increasing mubeta(1907) values up to 17,400 x 10(-48) esu.
authors: Departamento de Química Orgánica, Universidad de Zaragoza-CSIC, 50009 Zaragoza, Spain.
authors: Raquel
authors: R
authors: Andreu
authors: Laura
authors: L
authors: Carrasquer
authors: Santiago
authors: S
authors: Franco
authors: Javier
authors: J
authors: Garín
authors: Jesús
authors: J
authors: Orduna
authors: Natalia
authors: N
authors: Martínez de Baroja
authors: Raquel
authors: R
authors: Alicante
authors: Belén
authors: B
authors: Villacampa
authors: Magali
authors: M
authors: Allain