Sonication-assisted supramolecular nanorods of meso-diaryl-substituted porphyrins

Supramolecular nanorods of 5,15-diaryl-substituted porphyrins prepared by sonication method exhibit a broad absorption property, which is confirmed by photocurrent generation measurement in a photoelectrochemical cell.     

Functionalization of Diameter-Sorted Semiconductive SWCNTs with Photosensitizing Porphyrins: Syntheses and Photoinduced Electron Transfer

Covalent functionalization of diameter sorted SWCNTs with porphyrins (MP), and photochemistry to establish nanotube diameter-dependent charge separation efficiencies are reported. The MP-SWCNT(n,m) [M=2?H or Zn, and (n,m)=(7,6) or (6,5)] nanohybrids are characterized by a variety of spectroscopic, thermogravimetric, TEM imaging techniques, and also by DFT MO calculations. The thermogravimetric, Raman and fluorescence studies reveal the presence of a moderate number of porphyrins on the SWCNT surface. The MO results suggest charge separation (CS) via the excited state of MP. Time-resolved fluorescence studies reveal quenching of the singlet excited state of the MP with SWCNT(n,m), giving the rate constants of charge separation (k(CS) ) in the range of (4-5)×10(9) s(-1) . Nanosecond transient absorption measurements confirm the charge-separated radical cation and the radical anion as [MP(.+) -SWCNT(.-) ] with their characteristic absorption bands in the visible and near-IR regions. The charge separated states persist for about 70-100?ns thus giving an opportunity to utilize them to build photoelectrochemical cells, which allowed us to derive the structure-reactivity relationship between the nature of porphyrin and diameter of the employed nanotubes.     

Diameter‐Sorted SWCNT–Porphyrin and SWCNT–Phthalocyanine Conjugates for Light‐Energy Harvesting

A non‐covalent double‐decker binding strategy is employed to construct functional supramolecular single‐wall carbon nanotubes (SWCNT)–tetrapyrrole hybrids capable of undergoing photoinduced electron transfer and performing direct conversion of light into electricity. To accomplish this, two semiconducting SWCNTs of different diameters (6,5 and 7,6) were modified via π–π stacking of pyrene functionalized with an alkyl ammonium cation (PyrNH₃⁺). Such modified nanotubes were subsequently assembled via dipole–cation binding of zinc porphyrin with one ( 1 ) or four benzo‐18‐crown‐6 cavities ( 2 ) or phthalocyanine with four benzo‐18‐crown‐6 cavities at the ring periphery ( 3 ), employed as visible‐light photosensitizers. Upon charactering the conjugates using TEM and optical techniques, electron transfer via photoexcited zinc porphyrin and phthalocyanine was investigated using time‐resolved emission and transient absorption techniques. Higher charge‐separation efficiency is established for SWCNT(7,6) with a narrow band gap than the thin SWCNT(6,5) with a wide band gap. Photoelectrochemical studies using FTO/SnO₂ electrodes modified with these donor–acceptor conjugates unanimously demonstrated the ability of these conjugates to convert light energy into electricity. The photocurrent generation followed the trend observed for charge separation, that is, incident‐photon‐to‐current efficiency (IPCE) of a maximum of 12 % is achieved for photocells with FTO/SnO₂/SWCNT(7,6)/PyrNH₃⁺: 1 .