Modulation of Axial-Ligand Binding and Releasing Processes onto the Triazole-Bearing Nickel(II) Picket-Fence Porphyrins: Steric Repulsion versus Hydrogen-Bonding Effects

Abstract

N-(p-Methoxycarbonylbenzyl) triazole (BTz) substituents have been introduced to Ni(II) porphyrins (NiPs), in which their modulated axial-coordination processes have been investigated. For this study, the two types of ligands, neutral pyridine versus anionic cyanide, were employed to investigate an effect of BTz substituents. The unique microenvironments given by the BTz substituents provided two different effects on the axial-coordination processes of NiPs on the ground and excited states: (1) steric shielding and (2) donation of hydrogen-bonding sites. The steric shielding diminished the binding affinity of pyridine, while the cooperation of hydrogen bonds extraordinarily strengthened the binding affinity of CN(-). Interestingly, it was observed that the binding of CN(-) with the supporting of BTz substituents accompanied nonplanar distortion of NiPs. Such conformational change perturbed the electronic structure of NiPs, which gave rise to the modulation of coordination processes of NiPs in the excited state. As a consequence, photoinudced ligand binding and releasing processes of four- and six-coordinated NiPs were changed into the dominant photoinduced ligand releasing process.

Three-dimensional aromaticity in an antiaromatic cyclophane

“…While the TA spectra of 5 and 6 show that their excited-state dynamics are dominated by Ni-induced relaxation dynamics (Supplementary Figs. 8 and 9) 36,37 , the contrasting TA spectral features of 5 and 6 nicely illustrate the interactions between the norcorrole moieties in AN-cyclophane 5 . The TA spectrum of 6 , shows sharp and derivative-like TA spectral features at 520–650 nm.…”

Chirogenesis in Zinc Porphyrins: Theoretical Evaluation of Electronic Transitions, Controlling Structural Factors and Axial Ligation

“…Synthetic porphyrins also found a broad application in catalysis, [4–6] optical and chemo sensors, [7–15] light harvesting, [5,16–18] medicine, [19–22] supramolecular systems, [1,23–27] electronic devices, [11,28,29] etc. Specific natural and supramolecular chiral environment may result in chirogenic processes in porphyrin chromophores, which can be detected by various spectroscopic methods such as X‐ray, [30–33] IR, [31,34] Raman, [32] NMR, [31,32,35,36] circular polarized luminescence, [30,37,38] vibrational, [34,39,40] electronic (ECD), [9,19,41–44] and magnetic [34,45,46] circular dichroism.…”

“…Beside internal chemical modification of the porphyrin chromophore, external interactions, such as axial ligation, may play a significant role in the ECD behavior, since it affects the charge [79] and the spin state [52,80] of the central metal ion, the electronic configuration, [52,60,81–84] and the planarity of the porphyrin molecule [44,57,79,85–90] . Kolling et al., [91] Wang et al., [79] and Song et al [52] .…”

Synthesis of Di‐peri‐dinaphthoporphyrins by PtCl2‐Mediated Cyclization of Quinodimethane‐type Porphyrins

“…[17,18] Femtosecond transient absorption (TA) measurements were carried out for 8Ni and 10Ni. [19] On the other hand, the TA absorbance of 10Ni decays rapidly with two time constants of 1.2 and 12 ps.T he ultrafast relaxation dynamics can be comprehended by the optically dark state,c haracteristic of antiaromatic porphyrinoids. 8Ni exhibits ad ouble exponential decay profile (12 and 800 ps) without fluorescence emission.…”

“…This excited state dynamics of 8Ni can be explained by Ni II -centered (d,d) state of typical Ni II porphyrinoids,w here the excited population undergoes ar apid internal conversion (IC) process to the (d,d) state and subsequent deactivation process to the ground state on the order of hundreds ps. [19] On the other hand, the TA absorbance of 10Ni decays rapidly with two time constants of 1.2 and 12 ps.T he ultrafast relaxation dynamics can be comprehended by the optically dark state,c haracteristic of antiaromatic porphyrinoids. [16] Since the dark state acts as aladder in the deactivation process to the ground state, 10Ni shows fast IC process to the dark state with t = 1.2 ps and subsequent relaxation to the ground state with t = 12 ps.T wophoton absorption (TPA) measurements were carried out for 8Ni and 10Ni by using an open-aperture Z-scan method in the range of 1200-1900 nm, whereby one-photon absorption is negligible.T he TPAcross-section values are 190 GM for 8Ni at 1400 nm, and 380 GM for 10Ni at 1800 nm, respectively ( Figures S11-1, S11-2).…”