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

Abstract

Oxidative chemical vapour deposition of (5,15‐diphenylporphyrinato)nickel(II) (NiDPP) with iron(III) chloride as oxidant yielded a conjugated poly(metalloporphyrin) as a highly coloured thin film, which is potentially useful for optoelectronic applications. This study clarified the reactive sites of the porphyrin monomer NiDPP by HRMS, UV/Vis/NIR spectroscopy, cyclic voltammetry and EPR spectroscopy in combination with quantum chemical calculations. Unsubstituted meso positions are essential for successful polymerisation, as demonstrated by varying the porphyrin meso substituent pattern from di‐ to tri‐ and tetraphenyl substitution. DFT calculations support the proposed radical oxidative coupling mechanism and explain the regioselectivity of the C−C coupling processes. Depositing the conjugated polymer on glass slides and on thermoplastic transparent polyethylene naphthalate demonstrated the suitability of the porphyrin material for flexible optoelectronic devices.

Constitution and Conductivity of Metalloporphyrin Tapes

“…The distortion lowers the symmetry yielding mixed a 1u /a 2u radical cation character . Indeed, Ni II diphenyl porphyrins form double and triple linkages under oCVD conditions . A similar effect might be operative in copper(II) and iron(III) diphenyl porphyrins since both solution based, , and the present oCVD experiments yield doubly and triply‐linked copper(II) porphyrin tapes.…”

“…The generally accepted reaction mechanism of the oxidative C‐C coupling reaction between porphyrins starts with a nucleophilic attack of a neutral porphyrin at a porphyrin radical cation , , , , …”

“…Reducing the substituent size decreases the intermolecular distances, improves the interchain π–π stacking and thus facilitates interchain electron transfer in the film . Moreover, phenyl substituents with free ortho positions, allow dehydrogenative C–C coupling of the phenyl ring with the macrocycle during the oCVD process , . This intramolecular cyclization forces co‐planarity between the phenyl substituent and the porphyrin macrocycle.…”

“…To prevent the intramolecular cyclization as side reaction,, which would interfere with the mass spectrometric analysis of the double or triple intermolecular dehydrogenative coupling reaction by forming isobaric species, meso ‐mesityl substituents with blocked ortho positions were employed in the metalloporphyrin monomers.…”

Molecular flattening effect to enhance the conductivity of fused porphyrin tape thin films

“…28 The unique properties of fused porphyrins fostered the development of a wide series of synthetic strategies aiming to obtain directly fused porphyrins (porphyrin tapes) (Scheme 1). The main synthetic route towards directly fused porphyrins involves the solution-based dehydrogenative coupling of metalloporphyrins with transition metal salts such as AgX, 29 CuX 2 , 30,31 FeX 3 , 32 WCl 6 33 or organic oxidants such as [(p-Br-C 6 H 4 ) 3 N][SbCl 6 ], 34 or a mixture of 2,3-dichloro-5,6-dicyano-1,4benzoquinone and Sc(OTf) 3 . 16 Solution-based methods have enabled the preparation of fused porphyrin tapes from several metalloporphyrin complexes such as zinc(II), nickel(II), palladium(II) and copper(II).…”