Synthesis, spectroscopic, electrochemical redox, solvatochromism and anion binding properties of β-tetra- and -octaphenylethynyl substitutedmeso-tetraphenylporphyrins

Abstract

b-Tetra/octa-phenylethynyl substituted porphyrins and their metal (Co(II), Ni(II), Cu(II) and Zn(II)) complexes have been synthesized and characterized. H 2 TPP(PE) 8 exhibited a remarkable red shift in the Soret (Dl max ¼ 92 nm) band and longest wavelength band, Q x (0,0) (Dl max ¼ 117 nm), as compared to H 2 TPP. Interestingly, MTPP(PE) 8 exhibited a 450-500 mV anodic shift in the first ring reduction potentials as compared to MTPP which is ascribed to the electron accepting nature of phenylethynyl groups and extended p-conjugation whereas the first ring oxidation potentials remain unaltered. Hence, we observed a significant reduction in the HOMO-LUMO gap. The fluorescence quantum yields and lifetime values of the free base and Zn(II) porphyrins are found to be 10-20 and 2-6 times, respectively lower than MTPPs. These porphyrins display a strong solvatochromism that is reflected by a large red-shift in their absorption and emission maxima upon increasing the solvent polarity. These porphyrins exhibited lower radiative rate constants (k r ) and enhanced nonradiative rate constants (k nr ) as compared to MTPPs. The decrement in fluorescence lifetime values, quantum yields, radiative rate constants (k r ) and profound solvatochromism with enhanced nonradiative rate constants (k nr ) have been interpreted in terms of intramolecular charge transfer (ICT) from the porphyrin core to phenylethynyl moieties and extended p-conjugation. Further, ZnTPP(PE) 8 was utilized for the colorimetric "naked-eye" sensing of CN À , F À , Cl À , Br À , H 2 PO 4 À and CH 3 COO À ions through axial coordination of anions to Zn(II) metal centre. The electron deficient nature of the Zn(II) centre of ZnTPP(PE) 8 was further proved by axial ligation studies with anions in toluene.ZnTPP(PE) 8 exhibited extremely high binding constants (10 12 to 10 7 M À2 ) with anions. † Electronic supplementary information (ESI) available: Fluorescence, 1 H NMR and MALDI-TOF mass spectra, cyclic voltammograms, HOMO-LUMO diagrams, solvent dependent UV-visible and uorescence spectral proles, UV-Vis spectral titrations of ZnTPP(PE) 8 with different anions. See

Identification of Single-Atom Ni Site Active toward Electrochemical CO2 Conversion to CO

“…Using DFT (Supporting Information Note 4), which was confirmed to predict reliable E 0 for various Me−N 4 −TPP systems (Me = Fe, Co, Ni, Cu, and Zn) (Table S6), the E 0 of Ni-porphyrin compounds was theoretically investigated. DFT predicts the one-electron reduction potential of Ni−N 4 −TPP as −1.04 V SHE and the additional electron to be added to the π*-orbital of N 4 −TPP (Figure S25), which are in agreement with the previous experimental 44,45 and theoretical studies. 46 Electrochemical CO 2 -to-CO Conversion.…”

β‐Trisubstituted “Push–Pull” Porphyrins – Synthesis and Structural, Photophysical, and Electrochemical Redox Properties

“…The syntheses of H 2 TPPBr 2 NO 2 and H 2 TPPBr 2 CHO were achieved according to literature methods,, [12a] and they were utilized to prepare H 2 TPP(CH 3 ) 2 NO 2 ( 1 ) and H 2 TPP(CH 3 ) 2 CHO ( 2 ) in good yields (75–85 %) through Suzuki–Miyaura coupling reactions with methylboronic acid (Scheme ). Further, the appropriate metal complexes were synthesized from the corresponding metal acetates in quantitative yield . All of the newly synthesized porphyrins were characterized by UV/Vis, fluorescence, and 1 H NMR spectroscopy (Figures S1–S6 in the Supporting Information), MALDI‐TOF mass spectrometry (Figures S7–S16) and elemental analysis.…”

“…In addition to their biological demand, porphyrins are used in dye‐sensitized solar cells (DSSCs), nonlinear optics (NLO), ion sensing, catalysis, self‐assembly, and sorbents . The unsymmetrical β‐substitution fascinates porphyrin chemists owing to its existence in natural systems and it also exerts more favorable steric and electronic effects on the porphyrin π‐system compared to substituents at the meso ‐phenyl positions , . The redox properties of natural and synthetic porphyrins depend on the core structure, the type and location of the electron‐donating or ‐withdrawing β and meso substituents, the electronic nature and oxidation state of central metal ion, and the type and number of bound axial ligands.…”

Color Change Effect in an Organic–Inorganic Hybrid Material Based on a Porphyrin Diacid

“…These can then be reversed by heating in air. [88][89][90] Solvatochromic or vapochromic color changes are a ubiquitous phenomenon found in many fields of chemistry and biology, [91][92][93] as examples in the field of porphyrin compounds 94 and metal halides 95 show.…”

“…Photochromic effects in these compounds are induced with UV-light, triggering dramatic color changes, for example from colorless to black. These can then be reversed by heating in air. − Solvatochromic or vapochromic color changes are a ubiquitous phenomenon found in many fields of chemistry and biology, − as examples in the field of porphyrin compounds and metal halides show.…”