Gas Selective Ultrathin Organic Covalent Networks Synthesized by iPECVD: Does the Central Metal Ion Matter?

Abstract

The potential of porphyrin-derived metal organic covalent networks (OCN) thin films on light gas separations has been recently demonstrated. However, whether or not the central metal ion of the porphyrin plays a key role on separation performance has yet to be elucidated. Here, one metal-free and three metal-containing (zinc(II), manganese(III), and cobalt(II)) porphyrin-derived OCN thin films are successfully deposited on various substrates via an easily scalable initiated plasma-enhanced chemical vapor deposition approach. Among these four porphyrin-derived OCN thin films exhibiting superior light gas separation performances, three of them are synthesized for the first time. The gas permeation properties of these four OCN thin films suggest that the central metal ions neither significantly alter the packing structure of resulting OCN thin films, nor introduce facilitated transport phenomena favoring oxygen transmission. This observation is further validated by density functional theory calculations. Additional aging tests are also carried out to evaluate the physical aging behavior of the OCN thin films.

Reactivity of Nickel(II) Porphyrins in oCVD Processes—Polymerisation, Intramolecular Cyclisation and Chlorination

“…[14,30] Indeed, the mass spectrumo ft he oCVD NiTPP coating solely exhibits signals relatedt oN iTPP monomers (Figure 2a), while peaks corresponding to oligomers are additionally observedf or the oCVD NiP 3 Pa nd NiDPP coatings (Figure 2b and c). [22] During the oCVD process discussed here, NiP 3 Pc ould possibly exhibit similar reactivity to form short oligomers through b-meso or b-b linkages at the less hindered side of the porphyrin (Figure 2b,i nset). This is in contrast to the reaction of NiP 3 Pa nd iron(III) salts in solution, which gives mainly doubly andt riply linked dimers in ac ombined yield of 92 %.…”

“…[14] On the other hand, DFT calculations had suggested the possibility that in aCVD process tetraphenylporphyrins can undergo af ree-radical polymerisation reactiont hrough exo-pyrrole double bonds leading to as terically congested b-b linkedstaircases tructure. [22] During the oCVD process discussed here, NiP 3 Pc ould possibly exhibit similar reactivity to form short oligomers through b-meso or b-b linkages at the less hindered side of the porphyrin (Figure 2b,i nset). Clearly,l inkages involving the b positions are possible in CVD processes, yet they appear to be insignificant in solution processes involving NiP 3 P. In such congested b-meso or b-b connections,t he almostp erpendicular arrangementofthe monomericunits hampers p ex-tension and conjugation compared with doubly or triply linked NiDPP.L ess conjugation also explains the lower NIR absorbance of the oCVD NiP 3 Pc oatingc ompared to the oCVD NiDPP coating (Figure 1a and b).…”

“…[21] Recentg round-breaking studies also demonstrated successful free-radical polymerisation and oxidative polymerisation of porphyrins in CVD processes (Scheme 1). [22] On the other hand, the oxidative chemical vapourd eposition (oCVD)r eactiono f( 5,15-diphenylporphyrinato)nickel(II) (NiDPP,S cheme1)w ith FeCl 3 furnished p-conjugated poly(-NiDPP)t hin films by dehydrogenative CÀCc oupling. [23] The propagation reactiono ccurs at the b position of the porphyrin( 22 p electrons) and leads to ar educed porphyrin (chlorin with 20 p electrons).…”

“…[21] Recentg round-breaking studies also demonstrated successful free-radical polymerisation and oxidative polymerisation of porphyrins in CVD processes (Scheme 1). [20,22] Initiated plasma-enhanced CVD (iPECVD)o ff ree-base, manganese(III), cobalt(II) and zinc(II) 5,10,15,20-tetraphenylporphyrins [22] yielded polymeric films by free-radical polymerisation of one of the exo-pyrrole double bonds of the monomers (Scheme 1). [23] The propagation reactiono ccurs at the b position of the porphyrin( 22 p electrons) and leads to ar educed porphyrin (chlorin with 20 p electrons).…”

“…In these polychlorin thin films the monomers are covalently connected through bb linkages, yet p conjugationisa bsent (Scheme 1). [22] On the other hand, the oxidative chemical vapourd eposition (oCVD)r eactiono f( 5,15-diphenylporphyrinato)nickel(II) (NiDPP,S cheme1)w ith FeCl 3 furnished p-conjugated poly(-NiDPP)t hin films by dehydrogenative CÀCc oupling. These films show ar emarkably high conductivity of 3.6 10 À2 Scm À1 .…”