Chiral pyrrolo[1,2-a]quinolines as second-order nonlinear optical materials

The synthesis and nonlinear optical properties of a series of chiral pyrrolo[1,2-a]quinolines la-e is presented. The microscopic hyperpolarizabilities (beta(z)) were determined by EFISH measurements and the macroscopic susceptibilities (X2) were estimated by the Kurtz powder test. A small fixed angle of the annelated pyrrolidine donor unit with respect to the aromatic-pi-system renders the whole donor-pi-acceptor system chiral. The small deviation from planarity of approximately 10 +/- 3-degrees causes no observable reduction of the microscopic beta(z) value in comparison with the planar conjugated N,N- dimethylaniline analogues. The powder test showed phase matching for all pyrrolo[1,2-a]quinolines with an electron- withdrawing substituent at C-7 (1b-e). The aldehyde 1b crystallizes in the P2(1)2(1)2(1) space group and was calculated to have an efficiency of 8.3% of beta under optimal phasematch conditions. The nitro derivative 1c crystallizes in the favorable space group P2(1) (Z = 2) in which the angles of the two independent molecules with the optical b axis are 71.7- degrees and 43.5-degrees.