(a) Overview STM image (350 × 350 nm2) and close-up STM image (50 × 50 nm2) for submonolayer coverage of porphyrin 1 on Au(111) after adding Co atoms. Rosette structures and 1D polymer chains co-exist. (c) and (d) Zoom-in STM images (10 × 10 nm2) showing rosette structures of two different sizes. The rosette in (c) consists of 12 molecules: 4 molecules in the inner core and 8 molecules in the outer ring, while that in (d) is made up of 15 molecules: 5 molecules in the inner core and 10 molecules in the outer ring. The blue and green bars in (c) and (d) indicate the two different conformational isomers A and B, respectively (cf. Figure S5). The STM images were taken at 77 K with U = –1.8 V, I = 20 pA. The set of three arrows in (a) indicates the principal directions of