Immobilization of tetra-amine substituted metallophthalocyanines at gold surfaces modified with mercaptopropionic acid or DTSP-SAMs

This paper shows that amine substituted cobalt phthalocyanine (CoTAPc) can be deposited on gold surfaces by using an interconnecting layer of a self-assembled monolayer (SAM) of mercaptopropionic acid or Lomant's reagent (dithiobis(N-succinimidyl propionate) (DTSP)). In both cases the new bond formed is obtained by the creation of an amide. The layers were characterized by electrochemistry and showed high coverage fractions (near 100%). Reductive and oxidative desorption of the SAMs limit the useful potential window from −0.6 to +0.5 V versus Ag|AgCl. The SAM-CoTAPc layers show electrocatalytic activities towards oxygen reduction through the Co(I) central metal ion. The amount of CoTAPc molecules deposited (obtained from the Co central metal ion activity in nitrogen purged solutions) revealed that the CoTAPc molecules are bonded in a perpendicular manner at the surface. Taking into account a surface of 200 Å² for a flatly bonded MPc, this should result in a four times less amount of deposited CoTAPc compared to the experimental value obtained. Both methods showed good results and promising long-term stability and will be interesting tools for further research in surface modification and sensor development.