Unsymmetrical β-functionalized 'push-pull' porphyrins: synthesis and photophysical, electrochemical and nonlinear optical properties

• Published in: Dalton transactions : an international journal of inorganic chemistry Vol. 49; no. 1; pp. 3198 - 328
• Main Authors: Rathi, Pinki, Ekta, Kumar, Sandeep, Banerjee, Dipanjan, Soma, Venugopal Rao, Sankar, Muniappan
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 14.03.2020
• Subjects: Copper; Density functional theory; Dipole moments; Femtosecond pulses; Fluorescence; Mass spectrometry; Nickel; Nitrogen dioxide; NMR spectroscopy; Nonlinear optics; Optical properties; Photonics; Porphyrins; Reduction
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c9dt04252k

Two new series of β-triphenylamine-appended porphyrins (MTPP(TPA) 2 X, (where M = 2H, Co( ii ), Ni( ii ), Cu( ii ), Zn( ii ) and X = NO 2 /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) 2 NO 2 and CuTPP(TPA) 2 CHO exhibited an anodic shift by 0.44 and 0.36 V, respectively, as referenced to CuTPP, due to the electronic nature of β-substituents (NO 2 and CHO), which led to their easier reduction compared with CuTPP. H 2 TPP(TPA) 2 NO 2 and H 2 TPP(TPA) 2 CHO exhibited the largest resultant dipole moments (7.66 D and 4.55 D, respectively) as compared to H 2 TPP (0.052 D) due to the cross-polarized push-pull effect of β-substituents (NO 2 /CHO and triphenylamino groups) and the nonplanarity of the macrocyclic core. Third-order nonlinear optical properties of MTPP(TPA) 2 NO 2 and MTPP(TPA) 2 CHO (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. A new family of unsymmetrical β-TPA appended 'push-pull' porphyrins has been synthesized in good yield for the first time. They exhibited red shifted broad absorption spectral features with high dipole moments and tunable redox properties.