Highly polarizable chromophores for nonlinear optics:: syntheses, structures and properties of donor-acceptor substituted thiophenes and oligothiophenes

A series of new chiral donor-acceptor substituted mono- (1a,b), bi- (2a,b,f) and terthiophenes (3) as well as thienyl- and bithienylpyridinium salts 1d-f and 2i-k with various counterions has been synthesized. This class of thiophenes exhibit excellent molecular nonlinear optical properties such as second-order polarizabilities beta or second-order hyperpolarizabilities gamma. With respect to an application as nonlinear optical materials, some of these compounds have been investigated by Kurtz powder technique as well as by X-ray crystallographic analysis. The second-harmonic generation (SHG) powder efficiencies are measured at 1.064 mu m and 1.3 mu m with urea as reference. Furthermore, the influence of the chiral donors prolinol and methoxymethylpyrrolidine in the thiophene derivatives as well as the variation of counterions in the pyridinium salts on the orientation of the chromophores in the crystalline lattice was investigated, (C) 1998 Elsevier Science Ltd. All rights reserved.