Linear and V-shaped nonlinear optical chromophores with multiple 4H-pyran-4-ylidene moieties

A simple synthesis of dipolar one- and two-dimensional chromophores bearing two or three 4H-pyran-4-ylidene moieties is reported. Whereas the pyranylidene fragments acting as donors are proaromatic, the spacer one is not. In the linear derivatives, chain elongation gives rise to a sharp increase in the second order nonlinear optical responses, but some V-shaped derivatives display first hyperpolarizabilities (β) lower than those of their linear analogues. This uncommon feature lends experimental support to previous theoretical studies on the relative contribution and sign of the β-tensor components.Financial support from MICINNFEDER (CTQ2008-02942 and MAT2008-06522C02-02) and Gobierno de Aragón-Fondo Social Europeo (E39) is gratefully acknowledged. Predoctoral fellowships to E. Galán (CSIC, JAE 2008) and R. Alicante (FPI BES 2006- 12104) are also acknowledged.Peer Reviewe