Control of Porphyrin Planarity and Aggregation by Covalent Capping: Bissilyloxy Porphyrin Silanes

Abstract

Porphyrins are cornerstone functional materials that are useful in a wide variety of settings ranging from molecular electronics to biology and medicine. Their applications are often hindered, however, by poor solubilities that result from their extended , solvophobic aromatic surfaces. Attempts to counteract this problem by functionalizing their peripheries have been met with only limited success. Here, we demonstrate a versatile strategy to tune the physical and electronic properties of porphyrins using an axial functionalization approach. Porphyrin silanes (PorSils) and bissilyloxy PorSils (SOPS) are prepared from porphyrins by operationally simple κ4N-silylation protocols, introducing bulky silyloxy "caps" that are central and perpendicular to the planar porphyrin. While porphyrins typically form either J-or H-aggregates, SOPS do not self-associate in the same manner: the silyloxy axial substit-uents dramatically improve solubility by inhibiting aggregation. Moreover, axial porphyrin functionalization offers convenient handles through which optical, electronic, and structural properties of the porphyrin core can be modulated. We observe that the identity of the silyloxy substituent impacts the degree of planarity of the porphyrin in the solid state as well as the redox potentials. File list (2) download file view on ChemRxiv PorSil paper final.pdf (2.97 MiB) download file view on ChemRxiv PorSil SI final.pdf (18.18 MiB)

Accessible, Direct Photochemical Route for the Amine-Free Synthesis of Azoxybenzene and Functional Azoxy Derivatives via Nitroarene Homocoupling

“…The Soret band which absorbs around 420 nm is the most distinctive peak of the porphyrin UV-vis spectra and often the peak with the greatest intensity caused by the allowed transition to a higher energy state. 52 As with the Q bands, a redshift was observed in the Soret band after axial modification (Figure 32). Based on the absorption spectra, two different wavelengths of LEDs (405 nm and 455 nm) were used to excite these photocatalysts (Entry e and i, Table 5), where excitation at 405 nm was determined to promote the most photocatalytic activity.…”

“…Herein, I present a family of hypercoordinate porphyrin silanes as potential photocatalysts for reducing nitroarenes to aniline using visible light, including chloride, tributyl-, triphenyl-, or triisopropyl-siloxy axial coordination groups (Figure 30). 52 . These photocatalysts were systematically modified at the meso and axial positions to access an ample range of electrochemical properties rendering them potentially useful for a broad range of photocatalytic transformations.…”

“…Four Q bands absorbing from 580 to 650 nm correspond to the weak transition from the ground state to the first excited state. 52 The Q bands in porphyrin silanes are often bathochromically shifted compared to uncoordinated tetraphenyl porphyrins due to a decrease in the energy required for these transitions. Modifying the axial position of these catalysts can increase the intensity of one of the Q bands and result in the other three peaks being overshadowed (Figure 31).…”

“…Modified porphyrin silanes structures. These porphyrin silanes are used as the photocatalysts for reduction of nitroarenes 52.…”

Employing the thiol-ene click reaction via metal-organic frameworks for integrated sonodynamic-starvation therapy as an oncology treatment

“…They demonstrate that the UV-vis absorption shifted from 421 nm of Gd-TCPP to 416 nm of Gd-TCPP-NC [53][54][55], and the fluorescence emission at 651 nm of Gd-TCPP shifted to 646 nm of Gd-TCPP-NC [53,56]. Both the blue-shifted UV-vis and fluorescence spectra were due to the F atoms in NC having a stronger electronegativity [54,55]. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images (Fig.…”