Figure 2 The optimized structures of heterocyclic and amino-ethyl-amino modified dyes in dichloromethane. The grey, blue, red, yellow and white balls represent carbon, nitrogen, oxygen, sulfur and hydrogen atoms, respectively. Dihedral angles are α1, α2, α3 and α4 and bond lengths are r1, r2, r3, r4, r5 and r6.
As can be seen in Figure 2, after the introduction of the heterocycle, the donor moiety of the dye remains substantially planar except for the triphenylamine moiety. While the donor and acceptor exhibit distinct dihedral angles, in order to further illustrate the effect of the introduction of the heterocycle on the dye structure, we also listed in Table 1 the dihedral parameters of MTPABT-Pyc to MTPAPA-Pyc.
Table 1 Geometric parameters of heterocyclic modified dyes