Direct Emission of Continuously Varying Polarization of Light by Surface Treatment of a Mesogenic Luminophore

Abstract

Control of the polarized light generated from a luminophore has been intensively studied in organic light emitting diodes due to an enhancement of light intensity. The direct emission of highly circularly polarized light has been reported in a twist stacking of an achiral conjugated polymer by boundary surface effect without any chiral dopant. Although the twisted configuration of the emitting layer was obtained by applying different boundary conditions to two interfaces of the conjugated polymer, little study has been performed on the effect of the interfaces of the mesogenic polymer so far. Here, twist‐angle‐varying configuration in a single luminophore is designed and demonstrated to investigate an interfacial effect such as surface anchoring phenomena of conjugated mesogenic polymer. The continuously varying twisted configuration is fabricated by applying the circularly and unidirectionally rubbing method to the lower and the upper interfaces of the mesogenic luminophore, respectively. The surface anchoring and bulk elastic properties of luminophores are systematically analyzed to investigate twist deformation. Furthermore, a self‐luminous light source generating continuously varying polarization of light is demonstrated. The proposed light source can generate multi‐polarization states including linearly polarized, right‐handed circularly polarized, and left‐handed circularly polarized light in a single substrate.

Effects of molecular ordering on circularly polarized emission from a twisted mesogenic conjugated polymer

“…7 In the twisted stacks of the mesogenic luminophores, it is assumed that the F8BT film consists of uniformly twisted sublayers and the LP light emitted from an aligned sublayer within the EML experiences the phase retardation and changes to the other polarized light including CP light propagated through the twisted birefringent F8BT. 7,[11][12][13][14] In the PL process, the LP light is emitted from each sublayer and propagated in the twisted sublayers as shown in Fig. 1a (left image).…”

“…The twisted stacks of mesogenic luminophores induced by a chiral dopant or surface treatment of the EML lead to a high dissymmetry g factor. 4,7,[9][10][11][12][13] Here, linearly polarized (LP) light emitted from locally aligned conjugate polymers experiences birefringence passing through the twisted stacks of the mesogenic polymer and the CP light is extracted. In the twisted stacks of mesogenic luminophores, the dissymmetry g factor was governed by several parameters such as the total twisted angle, birefringence, and the location of the electron-hole recombination zone (the emission zone) within the EML.…”

“…In the twisted stacks of mesogenic luminophores, the dissymmetry g factor was governed by several parameters such as the total twisted angle, birefringence, and the location of the electron-hole recombination zone (the emission zone) within the EML. 7,[11][12][13][14] However, the twisted mesogenic luminophores on the well-controlled alignment layer produce the phase retardation of ambient light and consequently break the anti-reflection condition to eliminate reflection of ambient light. 7 Furthermore, the relationship between the dissymmetry factor and molecular ordering, directly related to the phase retardation of an EML, has not been fully analysed yet.…”

“…The dissymmetry g factors of the PL and EL devices with various total twisted angles (controlled by concentrations of the chiral dopant) and various order parameters (controlled by the contact distance) were experimentally measured and theoretically calculated based on the Mueller matrix analysis of the continuously twisted mesogenic sublayers, where the LP light emitted from the locally aligned mesogenic sublayer experiences birefringence passing through the twisted sublayers. 7,[11][12][13][14] The degree of LP light emitted from a certain mesogenic sublayer is governed by the order parameter which is controlled by the contact distance. That is, the degree of LP emission increases with the increasing order parameter.…”