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Charge‐Transfer‐Adaptable Double‐Strand Formation of a Porphyrin‐BODIPY‐Porphyrin Triad
Author(s) -
Morisue Mitsuhiko,
Kawanishi Miho,
Kusukawa Takahiro
Publication year - 2021
Publication title -
chemphotochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.13
H-Index - 18
ISSN - 2367-0932
DOI - 10.1002/cptc.202100025
Subject(s) - porphyrin , cyclohexane , chemistry , photochemistry , solvatochromism , intermolecular force , chromophore , solvation , solvent effects , solvent , crystallography , molecule , organic chemistry
A quadrupolar porphyrin–BODIPY–porphyrin array ( 1 ) displayed a moderate negative solvatochromism. The elastic 3,4,5‐tri(( S )‐dihydrocitronellyloxy)phenyl groups of 1 facilitated the solubility of such a polarized chromophore array in a nonpolar solvent, and 1 was assembled into a double‐strand as elucidated by extensive NMR spectroscopic experiments in [D 8 ]toluene and electronic absorption spectra in cyclohexane. Thermodynamic analyses revealed a small entropy change upon double‐strand formation, indicating that cyclohexane did not preferably solvate the porphyrin rings and BODIPY segment presumably because of their polarized nature. At the same time, the significant enthalpy change likely explained the intermolecular attractive force, such as the BF 2 ⋅⋅⋅Zn cation‐dipole interaction. The solvent polarity effect on the electronic spectra together with thermodynamic analyses suggested that the charge‐transfer (CT) character was decreased by the double‐strand formation in a nonpolar solvent. It was rationalized that insufficient solvent polarity stabilized the CT character of 1 only in part, and the residual polarization character might be stabilized by supramolecular assembly. The charge transfer character of 1 was stabilized by double‐strand formation which partially decreased the CT character enough to be stabilized by solvation with cyclohexane.