Two new photosensitizers featured with a cyanoacrylic acid electron acceptor (A) and a hybrid electron donor (D) of cyclopentadithiophene and dithiafulvenyl, either directly linked or separated by a phenyl ring, were synthesized and characterized. Both of them undergo two reversible oxidations and strongly absorb in the visible spectral region due to a photo-induced intramolecular charge-transfer (ICT) transition. To a great extent, the electronic interaction between the D and A units is affected by the presence of a phenyl spacer. Without a phenyl ring, the D unit appears more difficult to oxidize due to a strong electron-withdrawing effect of the A moiety. In sharp contrast, the insertion of the phenyl ring between the D and A units leads to a broken π-conjugation and therefore, the oxidation potentials remain almost unchanged compared to those of an analogue without the A group, suggesting that the electronic coupling between D and A units is relatively weak. As a consequence, the lowest-energy absorption band shows a slight hypsochromic shift upon the addition of the phenyl spacer, indicative of an increased HOMO–LUMO gap. In turn, the direct linkage of D and A units leads to an effective π-conjugation, thus substantially lowering the HOMO–LUMO gap. Moreover, the application in dye-sensitized solar cells was investigated, showing that the power conversion efficiency increases by the insertion of the phenyl unit.
合成并表征了两种新的光敏剂,其特点是具有氰基丙烯酸电子受体(A)和由环戊二硫苯和二硫富烯基组成的杂化电子给体(D),可以直接连接或通过苯环分离。它们都经历了两次可逆氧化反应,并且由于光诱导分子内电荷转移(ICT)跃迁,在可见光谱区强烈吸收。D和A单元之间的电子相互作用在很大程度上受到苯基间距的影响。没有苯环时,由于A基团的强电子吸引作用,D单元更难氧化。相比之下,将苯环插入D和A单元之间会破坏π-共轭,因此氧化电位与没有A基团的类似物相比几乎不变,表明D和A单元之间的电子耦合相对较弱。因此,最低能量吸收带在加入苯基间距后显示出轻微的向蓝移,表明HOMO-LUMO间隙增加。相反,D和A单元的直接连接导致有效的π-共轭,从而大大降低了HOMO-LUMO间隙。此外,还研究了其在染料敏化太阳能电池中的应用,插入苯基单元可以提高其功率转换效率。