MOLECULAR DESIGN AND PROPERTIES OF SIDE-CHAIN LIQUID-CRYSTAL POLYMERSFOR APPLICATIONS IN OPTOELECTRONICS

The synthesis of a number of side chain liquid crystalline polymers fo r quadratic non-linear optical (NLO) applications is reported, The act ive chromophore is a charge transfer (CT) biphenyl derivative which po ssesses mesogenic properties itself, The liquid crystalline behaviour of these polymers was established by differential scanning calorimetry (DSC), optical microscopy and X-ray diffraction. The active chromopho res were oriented by the standard corona poling technique and the degr ee of axial ordering was determined as a function of poling conditions by linear optical absorption. Growth of the second-harmonic generatio n (SHG) signal was used to probe the induction of polar order. These e xperiments clearly indicated that liquid crystallinity results in an e nhancement of the polar order over that of isotropic materials, The se cond-order NLO susceptibility tensor components d(31) and d(33) were m easured by the SHG technique, The ratio d(33)/d(31) was found to be mu ch larger than 3, in agreement with molecular statistical models, Valu es of d(33) up to 30-35 pm V-1 were obtained at 1064 nm fundamental wa velength. These values are essentially not resonance-enhanced, since t he chromophore absorption occurs below 350 nm. (C) 1998 John Wiley & S ons, Ltd.