Modulation Of Supramolecular Chirality Of Polydiacetylene Film With Azobenzene Chromophore

Chirality is a basic character of nature and appears at various hierarchical levels from molecular to supramolecular levels. Generally, the chirality of supramolecular systems can be generated through the assembly of chiral molecules or the combination of chiral and achiral molecules. On the supramolecular level, the spontaneous formation of chiral aggregates from achiral molecules is important and has currently received much attention. Interfacial assembly through the Langmuir-Blodgett (LB) technique offers excellent arenas for constructing supramolecular assemblies or ultrathin organized molecular films of the functional materials. By taking advantage of this technique, not only the molecular orientation but also the molecular arrangement as well as the aggregation can be modulated to some extent in a two-dimensional manner.Azobenzene chromophores were introduced into polydiacetylene system, and spontaneous symmetry breaking of the azobenzene-substituted diacetylene derivates could be achieved at the air/water interface, due to the overcrowded packing of adjacent azobenzene chromophores. Then the effects of circularly polarized light (CPL), template effect and hydrogen-bonding interaction on the supramolecular chirality of polydiacetylene were studied in detail. Besides, chiral induction, transfer, amplification, and memory were also investigated. At last, the circularly polarized UV light (CPUL) technique was also introduced into spin-coating films of azobenzene-substituted diacetylene derivates, succeeding in fabricating chiral polydiacetylene films.The π-π stacking between adjacent MADA (or NADA) molecules could contribute to the spontaneous overcrowded packing of the functional groups into a helical sense, so the transferred MADA (or NADA) LB films showed a chiral optical effect. The LB films could be polymerized to a designed chirality by utilizing CPUL. In this case, the chiral source was only CPUL, and the irradiation of left-and right-handed CPUL could definitely yield opposite chiral polymers. Induced chirality was shown to be maintained after the thermochromic phase transition. Chirality amplification and reversible chiroptical changes of PDA LB films upon thermal stimuli were demonstrated. A light-triggered reversible chiroptical switching between two enantiometric structures of PDA chains have been realized by alternating the stereoregular packing of azobenzene chromophores in the side chains with CPL treatment. Strong collective noncovalent interactions (π-π stacking) and rapid conformational rearrangement of the azobenzene chromophores under CPUL or CPL treatment are believed to be responsible for the supramolecular chirality formation and reversible chiroptical switches upon thermal and photic stimuli. This research provides novel model system for the understanding of the detailed mechanism of the chiroptical introduction and modulation in the PDA backbone.A CPL treated DBA monolayer could act as a chiral template to control the chirality formation of a PTDA LB films overlayer. However, the cis-form of azobenzene chromophores in the initial DBA monolayer was not favorable for the chirality formation of the transferred PTDA LB films. The molecular orientation and packing state of the azobenzene unit in the initial DBA monolayer played a key role in the chirality formation of the PTDA LB films overlayer. Further the configuration and chirality of PTDA/DBA hybrid films showed good thermo-stability. These results could benefit studies on the template-directed fabrication of the designed functional molecular arrangement, and the photo-chemical process showed here could be extended to studies of micropatterning of conjugated polymer films, which might provide a new tool for the fabrication of chiral organic devices in optoelectronics, electromagnetics and so on.The helical packing of PCDA assemblies and the resulting chiroptical properties of PDA LB films can be modulated by different azobenzene derivatives. The strong hydrogen-bonding interaction between PCDA and PAzo is suggested to be responsible for the regularly helical packing of PCDA molecules in the monolayer, resulting in chiral amplification of PDA LB films. While in NAzo/PCDA and MAzo/PCDA monolayer, PCDA molecules were in a loose packing similar as that in pure PCDA monolayer, and obvious microphase separation between PCDA assembles and MAzo (or NAzo) aggregates was observed, which was unfavourable for the helical formation of PDA LB films. Moreover, the chiroptical properties of PDA LB films derived from PAzo/PCDA co-assembled monolayer can be modulated by the photo-isomerization of the azobenzene chromophores in the monolayer. This work provides a novel model system that combines supramolecular chemistry and LB technique for the chiral regulation of PDA films.Thin intrinsically achiral PADA/PMMA hybrid films were prepared by spin-coating method. Striking CD signals for azobenzene chromophores and PDA chains were observed for the resulting PPADA/PMMA hybrid films irradiated with left-or right-handed CPUL. In this case, the chiral source was only CPUL. The photoinduced rearrangement of azobenzene chromophores and the interaction between the CPUL and the diacetylene dimmer were believed to be responsible for the supramolecular chirality formation in the hybrid films. After thermal treatment, chirality erasure of azobenzene chromophores was observed due to the thermal induced rearrangement and motions of azobenzene chromophores in the hybrid films. However, chirality amplification for polydiacetylene chains was obtained, which followed the’sergeants and soldiers’principle. This work not only provides novel model system for the understanding of the detailed mechanism of the chiroptical introduction in the PDA backbone but also is of great fundamental value for the rational design of novel optical and electro-magnetic devices based on azobenzene-substituted PDA materials.