Fig. 1: Schematic representation of size-matching strategy for facile identification of two types of conformations of model compound 1 with six formyl groups presented with red dots.

The three-dimensional molecule 1 experiences spontaneous interconversion between Conformer-1 with a pair of upper and lower clefts and Conformer-2 with a pair of left and right clefts (left column), of which C–C bonds a are much more liable to rotate than C–C bonds b, as the latter has a higher rotational energy barrier determined by relaxed potential energy scan (Supplementary Fig. 9). As revealed by molecular dynamics simulations, the permanently moving formyl groups are spotted within a projected circular ring with pink color (middle column), which is used to quantify the range covered by permanently moving formyl groups in each cleft. Considering the inner circle of the ring, i.e., the smallest possible size of the cleft, is different for Conformer-1 and -2, a small-sized CC-1 (with the amines presented with blue dots) and large-sized CC-2 (with the amines presented with green dots) are selected as size-matching conformational capturers (denoted as CC) by molecular dynamics simulations. Small-sized CC-1 exclusively captures and identifies Conformer-1, and large-sized CC-2 captures both Conformer-1 and -2 (right column).