Evidence of C–F···H–C Attractive Interaction: Enforced Coplanarity of a Tetrafluorophenylene-Ethynylene-Linked Porphyrin Dimer

Abstract

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.

Trimethylsilanolate-Promoted Activation of Alkynyl Trimethylsilanes: Hiyama-Type Sonogashira Cross-Coupling for the Synthesis of Arylene–Ethynylene-Linked Porphyrin Arrays

“…Then, the formidable purification using size-exclusion chromatography (SEC) is required to ensure the purity of 1 π satisfactory to photophysical investigations. , Therefore, the improved synthetic protocols of the Sonogashira cross-coupling reaction will open a new avenue to develop porphyrin-based materials. In our preceding study, we found that dichloromethane (DCM) is an effective solvent to minimize the Glaser homocoupling in Route B1 for the synthesis of 1 π in some cases. , This study extends the scope of the solvent-modulated approach (Route B1 ). Furthermore, we refined the Shultz’s approach and eventually developed a novel alternative methodology: the trimethylsilanolate-promoted Hiyama-type Sonogashira approach using potassium trimethylsilanolate (KOTMS) (Route B4 ).…”

“…At the first stage, we reconsider our strategy to achieve the exclusive Sonogashira cross-coupling conditions, the so-called solvent-modulated approach (Route B1 , Scheme ). The conditions also improved the isolated yield of 1 C6F4 (59%) . Herein, we extend the scope of the solvent-modulated strategy.…”

“…Yields of isolated products are estimated based on 3 π , to which 2.6 equiv of 2 was loaded. 1 Bpy , 1 C6F6 , and 1 C6H4 were previously reported.…”

“…By contrast, the isolation of 1 C6H4 was plagued by arduous repetition of the SCE purification to eliminate the byproducts that underwent the Glaser homocoupling . Moreover, the isolated yield of 1 Nph was low (15%) despite the structural isomer of 1 Azu .…”

Hydrogen-Bond-Promoted Planar Conformation, Crystallinity, and Charge Transport in Semiconducting Diazaisoindigo Derivatives

“…Stronger intramolecular hydrogen bonds (H-bonds) have also been used to lock the conformation of π-conjugated molecular systems. For the typical C–H···F, , C–H···O, , N–H···O, , and N–H···N interactions, the H-bond-induced stabilizations of coplanar conformations are in the range of 7–14 kcal/mol. Many literature examples exhibited intriguing properties induced by the coplanar conformation, such as anisotropic molecular aggregation, solvent resistance, and increased charge carrier mobility. ,,, Despite the potential of the H-bond approach, efficient synthetic strategies to incorporate robust intramolecular H-bonds into conjugated π-systems are still relatively limited.…”