PUB - Publikationen an der Universität Bielefeld

Recently the controversial discussion on the reliability of electrooptical relaxation data of polyelectrolyte systems has been revived. It can be shown that chemical-conformational contributions, for instance, to the dichroitic absorbance changes are exactly given by Delta A(CH)=(Delta A(parallel to) +2 .Delta(perpendicular to))/3, where Delta A(parallel to) and Delta A(perpendicular to) are the measured at the light polarization modes sigma=0 degrees (parallel to) and sigma=90 degrees (perpendicular to), respectively. Alternatively, Delta A(CH)=Delta A(sigma)* where sigma*=54.7 degrees is the magic angle (for small absorbance changes). If Delta A(sigma) is measured at the various sigma-polarization modes according to Delta A(sigma)=Delta A(parallel to) cos(2) sigma+Delta A(perpendicular to) sin(2) sigma, the exact value of Delta A(CH) is readily obtained. On the other hand, the linear dichroism Delta A=Delta A(OR)(parallel to) -Delta A(perpendicular to)=Delta A(parallel to) -Delta A(perpendicular to)+(Delta A(CH)(parallel to)-Delta A(CH)(perpendicular to)) can only be determined as an approximation of the difference Delta A(-)=Delta A(perpendicular to), if Delta A(CH)(parallel to) and Delta A(CH)(perpendicular to) are smaller or approximately equal.