Identification and electronic characterization of four cyclodehydrogenation products of H₂TPP molecules on Au(111)

Abstract

C–H bond activation and dehydrogenative coupling reactions have always been significant approaches to construct microscopic nanostructures on surfaces. By using scanning tunneling microscopy/spectroscopy (STM/STS) and non-contact atomic force microscopy (nc-AFM)...

Order, disorder, and metalation of tetraphenylporphyrin (2H-TPP) on Au(111)

“…13 Other thermally activated reactions may occur which change the structure of the macrocycle, such as cyclodehydrogenation of the ring structure (removal of hydrogen and formation of C-C bonds between the porphine and phenyl groups which flattens the porphyrin conformation). 14,15 The self-metalation of 2H-TPP on Au(111) is less well studied, partly due to the perception that gold is a relatively inert substrate. However, the uptake of gold into porphyrin macrocycles, to form a Au-TPP species, has recently been reported, 9 and novel methods of gold porphyrin synthesis are relevant due to a possible role as a functional species within anticancer complexes.…”

“…1a shows an STM topograph acquired at B 80 K where a variety of packing motifs were observed (see ESI †), however, the majority of close-packed structures are consistent with previously reported observations. 15,17,18 Annealing to 580 AE 50 K resulted in the loss of the close-packed phase and the formation of a 'diffuse phase', shown in Fig. 1b (imaged at 6.5 K).…”

On-Surface Synthesis of 2D Porphyrin-Based Covalent Organic Frameworks Using Terminal Alkynes

“…At this temperature, the benzene rings of the TEPP molecules were not yet planarized due to dehydrocyclization with the central pyrrole body. 43 Figure 3d shows the 3 × 3 2D COFs of TEPP molecules connected through linear couplings. The small-scale STM images show that these linear bonds are mainly of two types: the sp−sp carbon skeleton (diyne) generated by Glaser coupling (type-I reaction, Figure 3e) and the sp−sp skeleton (enyne) generated by nondehydrogenative head-tohead coupling (type-II reaction, Figure 3f).…”

“…After annealing at 550 K for 30 min (Figure d), more terminal alkynes reacted. At this temperature, the benzene rings of the TEPP molecules were not yet planarized due to dehydrocyclization with the central pyrrole body Figure d shows the 3 × 3 2D COFs of TEPP molecules connected through linear couplings.…”

Surface-Mediated Ring-Opening and Porphyrin Deconstruction via Conformational Distortion

“…Due to possible dehydrogenation at either side of the phenyl, four distinct PPDs (typically labeled A, B, C, and D in literature) could be expected. 25 Indeed, four structural isomers were reported on Ag(111), 24,25,40 Ag(100), 40 and Au(111) 26,27,41 surfaces, derived from different TPPs.…”