THE SYNTHESIS AND NONLINEAR-OPTICAL PROPERTIES OF (N-ALKYLPYRROL-2-YL)SQUARAINE DERIVATIVES .1.

The synthesis of a soluble poly(pyrrolylsquaraine) was achieved by N-a lkylation of the pyrrole nucleus with 1-bromooctadecane and subsequent condensation with squaric acid. Bis(1-octadecylpyrro1-2-yl)squaraine was also produced and found to exist in a variety of inseparable isome ric forms. When deposited as Langmuir-Blodgett monolayers on hydrophil ic substrates, these dyes exhibit second harmonic generation (SHG) wit h d(eff) = 0.5 +/- 0.1 pm V-1 for both. For comparison, bis(3,5-dimeth yl-1-octadecylpyrrol-2-yl)squaraine was synthesised and revealed a hig her SHG activity of d(eff) = 1.8 +/- 0.2 pm V-1. Poly(1-octadecylpyrro lylsquaraine) is the first alternating donor-acceptor polymer to give SHG.