A TD-DFT study of the effects of structural variations on the photochemistry of polyene dyes

We report a TD-DFT study of three polyene dyes namely: NKX-2553, NKX-2554 and NKX-2569 in isolation as well as upon their adsorption on TiO 2 nanoparticles. By choosing closely related dyes we wish to focus on the effects of structural variations on the absorption and charge-transfer properties of these systems. These three dyes show a non-intuitive trend in their respective efficiencies and therefore, were chosen to shed light on the structural components that contribute to this behaviour. Although NKX-2554 has an additional donor group, it is less efficient compared to the simpler NKX-2553 dye, that contains only one donor group. When the NKX-2554 structure is slightly modified by lengthening the linker group, one obtains the most efficient dye among this set, namely, NKX-2569. In this work, we show that the changes in the donor moiety has very little or no effect on the efficiency of these dyes, as can be seen in the case of NKX-2553 and NKX-2554. On the other hand, the improved performance of the NKX-2569titania complex can be understood to be a result of the longer linker group. A better understanding of these properties within different dyetitania complexes is important for the continual improvement of DSSCs. In this regards, this study will serve to provide guidelines to improve efficiencies of novel organic dyes. Relative probability densities of dyetitania complexes: (a) NKX-2553/TiO 2 and (b) NKX-2554/TiO 2 show direct charge transfer while NKX-2569/TiO 2 shows (c1) indirect as well as (c2) direct charge transfer mechanisms.