**3. Spectroscopic Characterization**

Newly synthesized FB analogs of LTAM molecules are not expected to be fully planar because of steric crowding, rather they can be viewed as a screw or helical, and thus may possess propeller structures. Subsequently, they can adopt a conformation where all three rings are twisted in the same direction, making a right- or left-handed propeller. As an analogy to a common screw or bolt, right- and left-handed screws are nominated as *M* and *P*, respectively, as shown in the upper line of Fig. 7. The red arrows denote the direction of bond rotation, not the helical direction (blue arrows). Two rings rotate through a perpendicular conformation while one moves in the opposite direction.

**Figure 7.** A new diastereomer can be formed via bond rotation (red arrows) of one diastereomer (blue arrows denote the helical direction between *M* and *P* isomers).

Theoretically, three configurational isomers, *ZE*, *EE,* and *ZZ,* can be proposed for these dyes. Since the *ZE* isomers can have *M* and *P* conformations, *ZE-*LTAM molecules can be obtained as a racemic mixture from the synthetic reaction described previously.
