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A Structural Model of Nitro‐Porphyrin Dyes Based on Spectroscopy and Density Functional Theory
Author(s) -
Farley Christopher,
Aggarwal Amit,
Singh Sunaina,
Dolor Aaron,
To Philip,
Falber Alexander,
Crossley Maxwell,
Drain Charles Michael
Publication year - 2018
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.24887
Subject(s) - porphyrin , nitro , chemistry , pyrrole , density functional theory , photochemistry , spectroscopy , computational chemistry , organic chemistry , physics , quantum mechanics , alkyl
Nitro‐porphyrins are an important class of commercial dyes with a range of potential applications. The nitro group is known to dramatically affect the photophysics of the porphyrin, but there are few systematic investigations of the contributing factors. To address this deficiency, we present spectroscopic studies of a series of nitro‐porphyrins, accompanied by density functional theory calculations to elucidate their structures. In particular, we explore how the positions of the substituents affect the energy levels and nuclear geometry. As expected, nitro groups on the meso‐phenyl rings cause small changes to the orbital energies by induction, while those at the β‐pyrrole positions more strongly conjugate into the aromatic system. In addition, however, we find evidence that β‐pyrrole nitro groups distort the porphyrin, creating two non‐planar conformations with distinct properties. This unexpected result helps explain the anomalous photophysics of nitro‐porphyrins reported throughout the literature, including inhomogeneous line broadening and biexponential fluorescence decay. © 2017 Wiley Periodicals, Inc.