N-Aromatic Complexation in Tetraphenyl Porphyrin Iron (III)-Pyridine: Evidence of Spin-Flip via Gas-Phase Electronic Spectroscopy

TY - JOUR

T1 - N-Aromatic Complexation in Tetraphenyl Porphyrin Iron (III)-Pyridine

T2 - Evidence of Spin-Flip via Gas-Phase Electronic Spectroscopy

AU - Uleanya, Kelechi O.

AU - Wilson, Sarah A.

AU - Dessent, Caroline E.H.

N1 - © 2024 The Authors. ChemPhysChem published by Wiley-VCH GmbH

PY - 2024/9/18

Y1 - 2024/9/18

N2 - There is growing interest in the electronic properties of metalloporphyrins especially in relation to their interactions with other molecular species in their local environment. Here, UV-VIS laser photodissociation spectroscopy in vacuo has been applied to an iron-centred metalloporphyrin (FeTPP+) and its N-aromatic adduct with pyridine (py) to determine the electronic effect of complexation. Both the metalloporphyrin (FeTPP+) and pyridine adduct (FeTPP+⋅py) absorb strongly across the spectral region studied (652–302 nm: 1.91–4.10 eV). Notably, a large blue shift was observed for the dominant Soret band (41 nm) upon complexation (0.47±0.02 eV), indicative of strong pyridine binding. Significant differences in the profiles (i. e. number and position of bands) of the electronic spectra are evident comparing FeTPP+ and FeTPP+⋅py. Time-dependent density functional theory calculations were used to assign the spectra, revealing that the FeIII spin-state flips from S=3/2 to S=5/2 upon complexation with pyridine. For FeTPP+, all bright spectral transitions are found to be π-π* in character, with electron density variously distributed across the porphyrin and/or its phenyl substituents. Similar electronic excitations are observed for FeTPP+⋅py, with an additional bright transition which involves charge transfer from the porphyrin to the pyridine moiety.

AB - There is growing interest in the electronic properties of metalloporphyrins especially in relation to their interactions with other molecular species in their local environment. Here, UV-VIS laser photodissociation spectroscopy in vacuo has been applied to an iron-centred metalloporphyrin (FeTPP+) and its N-aromatic adduct with pyridine (py) to determine the electronic effect of complexation. Both the metalloporphyrin (FeTPP+) and pyridine adduct (FeTPP+⋅py) absorb strongly across the spectral region studied (652–302 nm: 1.91–4.10 eV). Notably, a large blue shift was observed for the dominant Soret band (41 nm) upon complexation (0.47±0.02 eV), indicative of strong pyridine binding. Significant differences in the profiles (i. e. number and position of bands) of the electronic spectra are evident comparing FeTPP+ and FeTPP+⋅py. Time-dependent density functional theory calculations were used to assign the spectra, revealing that the FeIII spin-state flips from S=3/2 to S=5/2 upon complexation with pyridine. For FeTPP+, all bright spectral transitions are found to be π-π* in character, with electron density variously distributed across the porphyrin and/or its phenyl substituents. Similar electronic excitations are observed for FeTPP+⋅py, with an additional bright transition which involves charge transfer from the porphyrin to the pyridine moiety.

KW - Density functional theory

KW - Excited states

KW - Mass spectrometry

KW - Metalloporphyrin

KW - Molecular orbitals

UR - http://www.scopus.com/inward/record.url?scp=85208500713&partnerID=8YFLogxK

U2 - 10.1002/cphc.202400669

DO - 10.1002/cphc.202400669

M3 - Article

AN - SCOPUS:85208500713

SN - 1439-4235

JO - ChemPhysChem

JF - ChemPhysChem

M1 - e202400669

ER -