The formation of C–F···H–C “hydrogen bonds” has been a controversial subject because, in principle, fluorine is hardly an acceptor for less acidic protons contrasting to the C–F···H–O and C–F···H–N hydrogen bonds. Nevertheless, the interaction is emerging as a powerful implement for confining the torsional rotation in the design of fully coplanar π-conjugated polymers. Heretofore, no evidence of the C–F···H–C interaction has been observed in solutions. We herein disclose comprehensive evidence that the C–F···H–C interaction produces an attractive force. A 19F–1H heteronuclear Overhauser effect experiment elucidated the close proximity of the F and H atoms in the doubly edge-facing C–F···H–C interactions of a meso-tetrafluorophenylene-ethynylene-conjugated porphyrin dimer (1). Extensive electronic and photophysical property investigations confirmed that all the aromatic units were torsionally restricted by the C–F···H–C interactions. Moreover, the enforced coplanarity invoked a markedly high π-staking propensity. Thus, we have firmly established the formation of a C–F···H–C interaction that produces a hydrogen-bond-like attractive force in solution.

The first synthesis of the fully conjugated ethynylene‐linked polymer incorporating boron dipyrrine complex (BODIPY) and zinc porphyrin in the main chain was performed based on the exclusive Sonogashira polycondensation. Comprehensive experimental and theoretical investigations lead to an elaborate synthetic route to circumvent the possible side reactions of BODIPY in the presence of the palladium catalyst. Additionally, optimization of the synthetic conditions found that dichloromethane as the solvent suppresses the formation of the pseudo‐trans dimer of the copper acetylide and mitigates the undesired oxidative homocoupling reaction. Eventually, the exclusive Sonogashira polycondensation in dichloromethane provided the alternating BODIPY–porphyrin ethynylene‐conjugated polymer, which displayed absorption up to the near‐infrared wavelengths. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2457–2465

To synthesize meso-ethynylene-conjugated porphyrin arrays, the Sonogashira cross-coupling reaction is straightforward to construct the C­(sp)–C­(sp2) bonds, but the reaction is often accompanied by side reactions such as the Glaser homocoupling. The rate-determining oxidative addition step results in the unexpected kinetic competition with the Glaser homocoupling, which is desired to be circumvented. We here propose two sets of improved strategies for the synthesis of arylene–ethynylene-linked porphyrin arrays from the meso-brominated porphyrin and alkynes. First, we explored the solvent-modulated approach employing dichloromethane as the reaction solvent to minimize the formation of the copper acetylide dimer as the intermediate for the Glaser homocoupling, while the scope of the approach is limited. Subsequently, we have developed the trimethylsilanolate-promoted Hiyama-type approach that activates alkynyl trimethylsilanes (TMSs) by use of potassium trimethylsilanolate under amine-free conditions. The latter approach is advantageous not only in skipping the preprotodesilylation of the TMS group but also in achieving an excellent isolated yield.

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.

The Cover Feature illustrates how the charge‐transfer (CT) character of a quadrupolar porphyrin–BODIPY–porphyrin array is modulated depending on the solvent polarity. In cyclohexane, as a relatively poor solvent for the quadrupolar array, the structure adapted CT character for stable solubilization through double‐strand formation. The electronic properties were governed by solvent polarity parameters irrespective of assembly in either single‐ or double‐strand structures. More information can be found in the Article by Mitsuhiko Morisue and co‐workers.