Formation and photoinduced properties of zinc porphyrin-SWCNT and zinc phthalocyanine-SWCNT nanohybrids using diameter sorted nanotubes assembled via metal-ligand coordination and π–π stacking

Abstract

Photoinduced electron transfer processes in self-assembled zinc porphyrin (ZnP) or zinc phthalocyanine (ZnPc) with semiconducting (7,6)-and (6,5)-enriched SWCNTs were investigated. To bind photosensitizers to SWCNTs, first, pyrene covalently functionalized with a phenylimidazole (ImPyr) entity was treated with SWCNTs. Exfoliation of SWCNTs occurred due to π−π stacking of pyrene with nanotubes walls leaving the imidazole entity that was subsequently used to coordinate ZnP or ZnPc in o-dichlorobenzene (DCB). The donor-acceptor nanohybrids thus formed were characterized by TEM imaging, steady-state UV-visible-near IR absorption and fluorescence spectra. Free-energy calculations suggested possibility of electron transfer from the photoexcited ZnP or ZnPc to Im-Pyr/SWCNT(n,m) in the nanohybrids. Consequently, steady-state and time-resolved fluorescence studies revealed efficient quenching of the singlet excited state of ZnP or ZnPc with the rate constants of charge separation (k CS ) in the range of (3-6) × 10 9 s -1 . Nanosecond transient absorption technique confirmed the electron transfer products, ZnP •+ ←Im-Pyr/SWCNT •-and ZnPc •+ ←Im-Pyr/SWCNT •-(and opposite charged pairs) having characteristic absorptions with the decay rate constants due to charge recombination (k CR ) in the range of (1.4-2.4) × 10 7 s -1 , corresponding to lifetimes of radical ion-pairs in the 70-100 ns range. The SWCNT •-was further utilized to mediate electrons to hexyl-viologen dication (HV 2+ ) resulting in an electron-accumulation process in the presence of sacrificial electron donor, offering additional proof for the occurrence of photoinduced charge-separation and potential utilization of these materials in light energy harvesting applications. Further, photoelectrochemical cells have been constructed on FTO/SnO 2 electrodes to verify their ability to directly convert light into electricity. An IPCE efficiency of up to 7% has been achieved in case of ZnP←Im-Pyr/SWCNT modified electrode.

Design and photochemical study of supramolecular donor–acceptor systems assembled via metal–ligand axial coordination

“…The study revealed ultrafast energy transfer in the donor-acceptor dyads with time constants on the order of 2 -25 ps depending upon the type of dyad, as shown in Table 1 below. Similar results were obtained when ZnPc and ZnNc were replaced by MgPc and MgNc in DCB [102].…”

“…The imidazole groups were subsequently used to coordinate ZnP and ZnPc via the metal-ligand axial coordination as shown inFig. 50[135]. In this study, the nanohybrid of SWCNTs(n,m) with Pyr-Im was prepared by stirring SWCNTs andPyr-Im at ambient temperature for 48 hours in DMF as a solvent.…”

Photoinduced electron transfer processes of single-wall carbon nanotube (SWCNT)–based hybrids

“…Notably, pyrene was used as the linkage in some systems due to the strong π-π interaction between the pyrene and SWCNT [16]. A series of self-assembly zinc porphyrin derivatives noncovalently linked to SWCNT hybrids have been designed by D'Souza and Ito et al [8,[17][18][19][20][21][22], among which the self-assembly mechanisms like the metal-ligand axial coordination, ion pairing, hydrogen bonding and dipole ion pairing have all been reported. As shown in Figure 1a, the self-assembly (TMPyP + )Zn/PyrCOO − /SWCNT and (TPPS − )Zn/PyrNH 3 + /SWCNT hybrids were designed through ion paring [17].…”

Porphyrin‐Based Organophotocatalysts

“…FL quenching is commonly referred to as a useful fingerprint to probe the PET process. As in the case of single-wall carbon tube-zinc porphyrin (SWCNT-ZnP) hybrids (Figure 2A), steadystate and time-resolved FL studies ( Figure 2B) revealed efficient FL quenching of the singletexcited state of zinc porphyrin with the rate constants of charge separation in the range of (3-6) × 10 9 s −1 [90]. In addition, because of increased PET, a uniform film made of CNTs-porphyrin conjugates by simple filtration displayed high light-activated antimicrobial activity toward S. aureus with easy recovery [91].…”