| dc.description.abstract | In dye-sensitized solar cells (DSCs), dye molecules are responsible for absorbing light energy and generating photocurrent, making them a crucial factor influencing the photovoltaic conversion efficiency of the device. The use of photochromic molecules as dyes can enhance their application scope. However, to date, only fully organic photochromic dyes have been explored in DSC research. Therefore, this study focuses on the molecular design of two novel photochromic ligands, L66 and L68, which feature mono- and bis-3H-naphthopyran groups attached to a bipyridine core. These ligands were subsequently coordinated to ruthenium, forming the corresponding dye complexes, CYC-66 and CYC-68. Two synthetic approaches were attempted: one involved ligand exchange, facilitated by AgNO3, to remove chloride ions, thereby enabling the coordination of L66 or L68 to the ruthenium center; the other involved the synthesis of the ester derivatives, CYC-66 ester and CYC-68 ester, followed by different hydrolysis methods to obtain the target compounds. The 1H-NMR spectra measured before and after hydrolysis revealed that mild hydrolysis conditions were crucial for obtaining CYC-66 and CYC-68. Moreover, using an organic base (40 equivalents of NEt3) resulted in more excellent solution stability than using an inorganic base (45 equivalents of Na2CO3). CYC-66 and CYC-68, along with CYC-64 (which also contains two 3H-naphthopyran units), exhibited similar absorption bands within the range of approximately 295–550 nm, indicating comparable absorption properties in the ultraviolet-visible region. However, in the 325–375 nm range, slight differences were observed in the absorption shoulder peaks due to the π → π* transitions of the bipyridine and 3H-naphthopyran moieties. Additionally, CYC-68 and CYC-64 showed similar molar absorption coefficients, both approximately 1.2 times higher than that of CYC-66. Regarding device performance, the JSC values of all three dye-sensitized devices increased over time under illumination, exhibiting a photoactivation phenomenon regardless of the presence of a co-adsorbent. Among them, the CYC-68 sensitized devices (without BPHA) showed the most significant change, with JSC increasing from 3.29 mA·cm-2 to 4.63 mA·cm-2. After more than 1000 seconds of AM 1.5G illumination, the JSC values of the three devices became comparable: CYC-64 / CYC-64+BPHA at 4.49 / 6.09 mA·cm-2, CYC-66 / CYC-66+BPHA at 4.29 / 6.20 mA·cm-2, and CYC-68 / CYC-68+BPHA at 4.63 / 5.94 mA·cm-2. These data suggest that the mono-substituted 3H-Naphthopyran structure of CYC-66, due to its more suitable molecular size, enables a more compact arrangement upon adsorption onto TiO2, thereby enhancing light-harvesting efficiency. Consequently, after adding 5 mM BPHA, the power conversion efficiencies of the CYC-64, CYC-66, and CYC-68 sensitized devices reached power conversion efficiency (PCE) of 2.37%, 2.42%, and 2.32%, respectively. | en_US |