Emission ellipsometry used to probe aggregation of the luminescent 2,1,3-benzothiadiazole dyes and ordering in an E7 liquid crystal matrix

Unraveling the Morphology and Macroscopic Alignment of Poly(9,9-di-n-octylfluorenyl-2,7-diyl) for Enhanced Polarized Emission

“…This occurs with the NRSHT samples in Figures B and B as excitation with vertical polarization led to emission with vertical polarization (negative S 1 ), while excitation with horizontal polarization yielded emission in the horizontal direction (positive S 1 ). Therefore, the emission polarization was not due to the alignment of polymer molecules but rather to the polarization of the excitation, as reported in previous works. ,, For the RSHT samples, on the other hand, excitation with either vertical or horizontal polarization led to emission with vertical polarization (negative S 1 ), but the polarization degree and the S 1 values are smaller in modulus (see Figures and ). Emission occurs with polarization in the vertical direction, even with a horizontal excitation, because the molecules oriented in the horizontal direction will absorb the light preferentially and they will transfer energy to those oriented in the vertical direction.…”

“…In order to verify the polarization state of the emitted light, ellipsometry measurements , were performed. The polarized emitted light was determined from the Stokes parameters using the equations proposed in refs and . where S 0 , S 1 , S 2 , and S 3 are the Stokes parameters and the polarization degree is given by …”

“…Emission occurs with polarization in the vertical direction, even with a horizontal excitation, because the molecules oriented in the horizontal direction will absorb the light preferentially and they will transfer energy to those oriented in the vertical direction. The latter will then be responsible for emission . This indicates that polarized emission for RSHT is due to energy-transfer processes, in which molecules with a dipole transition moment, or at least some component of it, in the direction of excitation polarization have a higher probability to absorb. , The resulting emission is then partially polarized in the direction of light excitation due to energy transfer from photoexcited carriers .…”

“…A broad, practically symmetrical band from 320 to 430 nm characterizes the optical absorption of the PFO nematic phase (N) . The spectra from the polarized absorption measurements performed as given in ref are shown in Figure B for the RSHT sample. The differences between the spectra can be explained as follows.…”

Achromatic Ellipsometry: Theory and Applications

“…Basically, it consists of a mixture of LC 5CB (47%), 7CB (25%), 8OCB (18%), and 5CT (10%), doped with a luminescent dye 4,7-bis {2-[4-(4-decylpiperazin-1-yl) phenyl]ethynyl}-[2,1,3]-benzothiadiazole (5A) at 0.025% of molar concentration [20]. Cells were prepared by superimposing two BK7 glass substrates coated with Poly(vinyl alcohol) (PVA) films separated by 20 mm thick Mylar spacers.…”