Evolution of the characterization of horizontally aligned organic light-emitting molecules and their recent progress of molecular design

This review article surveys the organic small molecular materials, light-emitting for most of them, being studied for the molecular alignment or orientation in thin films. Following a chronicle order, three practical characterization techniques, variable angle spectroscopic ellipsometry (VASE), angle-dependent photoluminescence (ADPL), and grazing incidence wide-angle x-ray scattering (GIWAXS) have been used to probe phosphorescence, thermally activated delayed fluorescence (TADF) materials, as well as those of non-phosphorescence and non-TADF materials.