On the Electro-optical Properties of Metallo-supramolecular Polyelectrolytes (MEPEs) Containing Copper(I) and Their Electrochromic Applications

In this thesis, a new field in electrochromic materials combining inorganic metal ions with organic ligands, which is called metallo-supramolecular materials, is introduced and discussed. The metallo-supramolecular polyelectrolytes (MEPEs) containing copper(I) metal ion, MEPE-Cu(I), is first synthesized and applied in electrochromism. To investigate different roles in electrochromic device, polyaniline-carbon nanotube (PANI-CNT) and poly(3,3-diethyl-3,4-dihydro-2H-thieno-[3,4-b][1,4]dioxepine) (PProDOT-Et2) are chosen with MEPE-Cu(I) for device fabrications. We choose 4’-4’’’’-(1,4-phenylene) bis (2,2’:6’,2’’-terpyridine) as the ligand and copper(I) acetate as metal ion center to synthesize the MEPE-Cu(I). Due to metal-to-ligand charge transfer (MLCT) and redox reaction of Cu(I)/Cu(II), the color could be change by applying potential to influence the interaction between Cu(I) and terpyridine ligands and becomes as a new cathodic coloration material. All the MEPE-Cu(I) thin films are prepared by drop-coating with a concentration of 1 mg/mL. By varying the volume per drop, four different thicknesses of MEPE-Cu(I) films (MEPE-Cu(I) 100 μL to 400 μL) are prepared and compared. And the limitation of thickness for MEPE-Cu(I) have been found. The cyclic-voltammetry (CV) pretreatment between 0.0 V and 1.5 V (vs. Ag/Ag+) for 100 cycles is applied for preparation of MEPE-Cu(I) thin film, which enhance the optical performance and reduce resistance of thin film in electrochemical reaction to reach stability of the film. It is also proved by SEM image for surface morphology and EQCM for mass change. MEPE-Cu(I) has transmittance change of above 20%, less 1s of response time and the coloration efficiency of around 260 cm2/C. With ultra-fast response time and higher coloration efficiency, MEPE-Cu(I) could be chosen to apply for electrochromic applications. Two electrochromic devices based on MEPE-Cu(I) with TBAP/ACN as electrolyte have been fabricated. In MEPE-Cu(I)/PANI-CNT ECD system, PANI-CNT as an anodic coloration material is selected as an ionic storage layer with higher charge capacity, which provide better ability of electron transfer for MEPE-Cu(I) and enhance the electrochromic properties. The transmittance change at 580 nm is similar to MEPE-Cu(I) thin film. However, the response time could be shortened to less than 0.5 s. In the long-term stability experiment, the device could be operated for 1500 cycles and maintains above 99% of original performance. Besides, in MEPE-Cu(I)/PProDOT-Et2 ECD, PProDOT-Et2 is selected as the main electrochromic layer to fabricated with MEPE-Cu(I) because of relatively smaller transmittance change. MEPE-Cu(I) could also act as an ionic storage layer and assist the electron transfer of PProDOT-Et2, which provides higher transmittance above 35%, fast response time of less than 1 s. In spite of larger operating potential window of 3.5 V, the device could be operated for 1000 cycles with only 6.3% of decay. Both these two devices prove that MEPE-Cu(I) could be a stable electrochromic material and worth applying for other applications