Highly Ordered 2D‐Assemblies of Phase‐Segregated Block Molecules for Upconverted Linearly Polarized Emission

Abstract

Materials based on the laminar ordering of self‐assembled molecules have a unique potential for applications requiring efficient energy migration through densely packed chromophores. Here, employing molecular assemblies of coil–rod–coil block molecules for triplet–triplet annihilation upconversion (TTA‐UC) based on triplet energy migration with linearly polarized emission is reported. By covalently attaching discrete‐length oligodimethylsiloxane (oDMS) to 9,10‐diphenylanthracene (DPA), highly ordered 2D crystalline DPA sheets separated by oDMS layers are obtained. Transparent films of this material doped with small amounts of triplet sensitizer PtII octaethylporphyrin show air‐stable TTA‐UC under non‐coherent excitation. Upon annealing, an increase in TTA‐UC up to two orders of magnitude is observed originating from both an improved molecular ordering of DPA and an increased dispersion of the sensitizer. The molecular alignment in millimeter‐sized domains leads to upconverted linearly polarized emission without alignment layers. By using a novel technique, upconversion imaging microscopy, the TTA‐UC intensity is spatially resolved on a micrometer scale to visually demonstrate the importance of molecular dispersion of sensitizer molecules for efficient TTA‐UC. The reported results are promising for anti‐counterfeiting and 3D night‐vision applications, but also exemplify the potential of discrete oligodimethylsiloxane functionalized chromophores for highly aligned and densely packed molecular materials.

Organic Polymer Hosts for Triplet–Triplet Annihilation Upconversion Systems

“…111 There are many materials that show great promise to be developed into TTA-UC host systems. 112,113 One such example was reported by Kim et al, who developed a quantum dot/siloxane composite film, which is exceptionally stable against heat and moisture. 113 The film showed excellent dispersion of the nanocrystals and favorable mechanical properties and could be potentially used to load chromophores, which could be encapsulated in the matrix by the high degree of siloxane bond formations and cross-linked bonding.…”

“…Some studies have already been conducted on TTA-UC systems using semiconducting inorganic nanoparticles that can act as a sensitizer with an organic substrate grafted to the particle acting as an emitter. ,, Inorganic materials usually provide more mechanical structure and an improved barrier to oxygen for the system and are often more photostable, while the presence of a grafted organic polymer maintains the processability of lightweight polymeric materials . There are many materials that show great promise to be developed into TTA-UC host systems. , One such example was reported by Kim et al, who developed a quantum dot/siloxane composite film, which is exceptionally stable against heat and moisture . The film showed excellent dispersion of the nanocrystals and favorable mechanical properties and could be potentially used to load chromophores, which could be encapsulated in the matrix by the high degree of siloxane bond formations and cross-linked bonding.…”

Highly Ordered Supramolecular Materials of Phase‐Separated Block Molecules for Long‐Range Exciton Transport

“…Recently, oligodimethylsiloxane ( o DMS) side chains have been attached to various aromatic cores to create highly ordered structures at the nanoscale. [ 16–22 ] In one such example, domains of millimeter‐sized aligned 2D crystalline sheets could be obtained by slow cooling from their melt. [ 16 ] For this purpose, o DMS blocks of discrete length are covalently linked to diphenylanthracene (DPA).…”

“…[ 16–22 ] In one such example, domains of millimeter‐sized aligned 2D crystalline sheets could be obtained by slow cooling from their melt. [ 16 ] For this purpose, o DMS blocks of discrete length are covalently linked to diphenylanthracene (DPA). In this system, the nanophase separation of o DMS with the aromatic core leads to highly ordered 2D DPA sheets separated by o DMS layers.…”

“…Branched Si 15b can also be considered as two o DMS side chains of length 7, and it is known that shorter o DMS side chains often lead to higher melting temperatures. [ 16 ] Upon further heating, the materials became isotropic between 210 and 255 °C for CBT(Si 15 ) 3 and between 180 and 255 °C for CBT(Si 15b ) 3 . The loss of birefringence is related to the breaking of the CBT–CBT interactions and the resulting loss of order.…”