Communication: Substrate induced dehydrogenation: Transformation of octa-ethyl-porphyrin into tetra-benzo-porphyrin

Abstract

Faculty of Physics and Center for Nanointegration Duisburg-Essen (CENIDE), University of 47048 Duisburg, Germany (Received 27 March 2013; accepted 29 May 2013; published online 7 June 2013) Individual molecules of octa-ethyl-porhphyrin-iron(III)-chloride adsorbed on a Cu(111) surface are studied by scanning tunneling microscopy. Upon moderate heating the molecules are found to transform into Fe-tetra-benzo-porphyrin at a surprisingly low temperature of 380 K. If the annealing is interrupted, the different steps of the transformation can be imaged. By evaluating the ratio of transformed molecules as function of annealing temperature, an approximate activation energy of 1.2 eV ± 0.1 eV could be determined. © 2013 AIP Publishing LLC.

Dehydrocyclization of peripheral alkyl groups in porphyrins at Cu(100) and Ag(111) surfaces

“…These changes, taken together, indicate a chemical transformation of the peripheral ethyl groups to aromatic benzo groups, i.e., a dehydrocyclization (Scheme 1). The temperature of 500 K is consistent with other studies of dehydrogenation of ethyl groups and C-H bond scission on Cu and other surfaces [59,83]. The dehydrocyclization of OEP on Cu(100) at 500 K (15 minute anneal) ( Fig.…”

“…The dehydrocyclization of OEP on Cu(100) at 500 K (15 minute anneal) ( Fig. 2) is higher in temperature than a previous report for the dehydrocyclization of Fe-OEP on Cu(111) at 430 K (60 minute anneal) [59].…”

“…4A and 4B). The temperature of dehydrocyclization on Ag(111) at 600 K is higher than measurements on the (111) surfaces of metals in the same group; dehydrocyclization has been reported for Fe-OEP on Cu(111) at 430 K [59] and for H 2 -OEP on Au(111) at 530 K [58]. Dehydrocyclization on each of those surfaces occurs at significantly higher temperatures than on Pt(111) (300 K) [31] or on Cu 3 Pt(111) (393 K) [26,29,30].…”

“…There have been several examples of cyclodehydrogenation of aromatic rings on Cu(111) or Pt(111) [52,53], including some that formed more extended polyaromatic structures [54][55][56][57]. Previous dehydrocyclization studies of alkane substituted porphyrins used Fe-OEP, which was characterized through Kondo resonance and scanning tunneling microscopy (STM) on Cu 111and Au(111) [58,59]. In these studies, porphyrin molecules were stable on the surface up to temperatures of 430 K on Cu(111) and 530 K on Au(111) where dehydrocyclization of the alkanes took place.…”

Self-assembly and coverage dependent thermally induced conformational changes of Ni(ii)-meso-tetrakis (4-tert-butylphenyl) benzoporphyrin on Cu(111)

“…47 Moreover, Vörden et al demonstrated that the Cu(111) surface induced the transformation of octa-ethyl-porphyrin to tetra-benzo-porphyrin with an activation energy of B1.2 eV. 48 Most relevant are the findings by Xiao et al,…”