The development of high-performance and cost-effective catalysts for the oxygen reduction reaction (ORR) is essential for the advancement of fuel cells. In this work, three different functionalized cobalt porphyrins, meso-tetraphenylporphyrinatocobalt(II) (CoTPP), meso-tetrakis(4′-hydroxyphenyl)porphyrinatocobalt(II) (CoTHPP) and meso-tetrakis(4′-carboxy-phenyl)porphyrinatocobalt(II) (CoTCPP), are prepared. These porphyrins are immobilized non-covalently on multiwalled carbon nanotubes (MWCNTs) and used for the ORR in 0.1 M HClO₄, 0.1 M phosphate buffer solution (pH 7.0) and 0.1 M KOH media. The composite materials are characterized by using spectroscopic and electrochemical techniques and their oxygen reduction efficiencies are compared in different media. Kinetic interpretations and hydrodynamic voltammetry (in three media) studies demonstrated that the MWCNT–CoTPP, MWCNT–CoTHPP and MWCNT–CoTCPP composite materials exhibit significant efficiency with decreased overpotential, considerable methanol tolerance and long term operational stability (up to 3000 cycles) for the ORR similar to commercially available platinum carbon (Pt–C) catalysts. These results reveal that the new MWCNT–cobalt porphyrin composite materials can be a potential alternative to the expensive Pt–C catalysts or other commercial cathode materials in fuel cells.

Two new series of β-triphenylamine-appended porphyrins (MTPP(TPA)₂X, (where M = 2H, Co(II), Ni(II), Cu(II), Zn(II) and X = NO₂/CHO) have been synthesized and characterized by various spectroscopic techniques, namely, UV-vis, fluorescence, NMR spectroscopy, mass spectrometry, cyclic voltammetry, density functional theory and ultrafast nonlinear optical (NLO) studies. They exhibited 16–22 nm and 39–58 nm red-shifts in the Soret and Q_x(0,0) bands, respectively, as compared to MTPPs due to the resonance and inductive effects of β-substituents on the porphyrin π-system. The first reduction potential of CuTPP(TPA)₂NO₂ and CuTPP(TPA)₂CHO exhibited an anodic shift by 0.44 and 0.36 V, respectively, as referenced to CuTPP, due to the electronic nature of β-substituents (NO₂ and CHO), which led to their easier reduction compared with CuTPP. H₂TPP(TPA)₂NO₂ and H₂TPP(TPA)₂CHO exhibited the largest resultant dipole moments (7.66 D and 4.55 D, respectively) as compared to H₂TPP (0.052 D) due to the cross-polarized push–pull effect of β-substituents (NO₂/CHO and triphenylamino groups) and the nonplanarity of the macrocyclic core. Third-order nonlinear optical properties of MTPP(TPA)₂NO₂ and MTPP(TPA)₂CHO (M = 2H and Zn(II)) were investigated in a broad spectral range (680–850 nm) using the Z-scan technique with femtosecond 80 MHz pulses. These materials demonstrate strong nonlinear optical coefficients, endowing them with potential for prominent photonic applications.

β-Dicyanovinyl substituted porphyrins have been synthesized and utilized as chemodosimeters for ratiometric and colorimetric sensing of cyanide ions in CH₃CN and H₂O/CH₃CN mixture.