4H-Pyran-4-ylidenes: strong proaromatic donors for organic nonlinear optical chromophores.
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.
Andreu
Raquel
R
Departamento de Química Orgánica, Universidad de Zaragoza-CSIC, 50009 Zaragoza, Spain.
Carrasquer
Laura
L
Franco
Santiago
S
Garín
Javier
J
Orduna
Jesús
J
Martínez de Baroja
Natalia
N
Alicante
Raquel
R
Villacampa
Belén
B
Allain
Magali
M