Systematic Studies on the Effect of Fluorine Atoms in Fluorinated Tolanes on Their Photophysical Properties

Diverse Synthetic Transformations Using 4-Bromo-3,3,4,4-tetrafluorobut-1-ene and Its Applications in the Preparation of CF2 CF2 -Containing Sugars, Liquid Crystals, and Light-Emitting Materials

Organic molecules with fluoroalkylene scaffolds, especially a tetrafluoroethylene (CF2 CF2 ) moiety, in their molecular structures exhibit unique biological activities, or can be applied to functional materials such as liquid crystals and light-emitting materials. Although several methods for the syntheses of CF2 CF2 -containing organic molecules have been reported to date, they have been limited to methods using explosives and fluorinating agents. Therefore, there is an urgent need to develop simple and efficient approaches to synthesize CF2 CF2 -containing organic molecules from readily available fluorinated substrates using carbon-carbon bond formation reactions. This personal account summarizes the simple and efficient transformation of functional groups at both ends of 4-bromo-3,3,4,4-tetrafluorobut-1-ene and discusses its synthetic applications to biologically active fluorinated sugars and functional materials, such as liquid crystals and light-emitting molecules.

Development of Donor-π-Acceptor-Type Fluorinated Tolanes as Compact Condensed Phase Luminophores and Applications in Photoluminescent Liquid-Crystalline Molecules

Fluorinated tolanes, produced by introducing fluorine atoms into one of the aromatic rings of tolane, emitted almost no fluorescence in a solution state, but the fluorescence intensity increased dramatically in the crystalline state because of intermolecular H⋅⋅⋅F hydrogen bonds. The photoluminescent (PL) colors depend on the molecular orbitals, dipole moments, and molecular aggregated structures can be varied by controlling terminal substituents along the major molecular axis. The introduction of a long alkoxy or semifluoroalkoxy unit as a flexible chain into the terminal positions along the major molecular axis induced the formation of a liquid-crystalline (LC) phase; fluorinated tolanes act both as luminophores and as mesogens, leading to the molecular design of new photoluminescent LC molecules (PLLCs). The results also indicated that a fluorinated tolane dimer, which consists of two fluorinated tolanes linked by a flexible alkylene spacer, also becomes a novel PLLC.

Revisiting the bases of the excited states for solvated fluorinated benzenes and pentafluorophenylalanine

Vapor-phase molecular simulation studies of aromatic compounds with five or more fluorine atoms on the ring reveal emission spectra characterized by S₀ → πσ* and πσ*→S₀ transitions. In this study, the absorption, excitation, and solvent-dependent emission spectra of fluorinated benzenes, including pentaflurophenyalanine (F5Phe), which is a potential marker for biochemical research, were collected and compared to the results of the simulation. Time-dependent self-consistent field (TD-SCF) density functional theory (DFT) calculations were performed to examine the nature of excited states and relevant photo-physical processes. The results show that pentafluorobenzene (PFB) and hexafluorobenzene (HFB) show behavior consistent with the vapor phase simulation studies, that tracts well with benzenes substituted with fewer fluorine atoms. For example, 1,2,3-trifluorobenzene (123TFB) and 1,2,3,4-tetrafluorobenzene (1234TFB) show emission spectra with varying intensities of tails and shoulders. Those features are attributed to πσ*→S₀ transitions where the πσ* state has been stabilized in the presence of solvents like water, acetonitrile, and isopropanol, which are different from their simulated behavior in the gas phase. The emission in water solvent especially shows a significant increase in the emission intensity at 310 nm, which is common for all studied samples. The emission spectrum of F5Phe closely reflects that of PFB, which arises from the interplay of both ππ *→S₀ and πσ*→S₀ transitions. Also, it is observed that the interaction between adjacent σ* orbitals of C-F bond for 123-TFB, 1234-TFB, 12345-PFB, and 123456-HFB contributes to further narrowing the energy gap between S₀ and S₁ states with a significant red shift on the emission spectra compared to their isomers.

Development of Yellow-to-Orange Photoluminescence Molecules Based on Alterations in the Donor Units of Fluorinated Tolanes

Since the aggregation-induced emission (AIE) phenomenon was first reported by Tang et al., much effort has been devoted to the development of solid-state luminescent molecules by chemists worldwide. Our group successfully developed fluorinated tolanes as novel compact π-conjugated luminophores with blue photoluminescence (PL) in the crystalline state. Moreover, we reported the yellow-green PL molecules based on their electron-density distributions. In the present study, we designed and synthesized fluorinated tolanes with various amine-based donors and evaluated their photophysical properties. The carbazole-substituted fluorinated tolane exhibited strong PL in the solution state, whereas piperidine- or phenothiazine-substituted fluorinated tolanes showed a dramatic decrease in PL efficiency. Notably, fluorinated tolanes with piperidine or phenothiazine substituents displayed yellow-to-orange PL in the crystalline state; this may have occurred because these tolanes exhibited tightly packed structures formed by intermolecular interactions, such as H···F hydrogen bonds, which suppressed the non-radiative deactivation process. Moreover, fluorinated tolanes with amine-based donors exhibited AIE characteristics. We believe that these yellow-to-orange solid PL molecules can contribute to the development of new solid luminescent materials.

D–π–A-type fluorinated tolanes with a diphenylamino group: crystal polymorphism formation and photophysical behavior

Ph2N-Substituted fluorinated tolanes produced two polymorphisms, which display a distinct photoluminescence behavior; one polymorphism showed green PL and the other exhibited yellow PL.

Fluorinated tolane-based fluorophores bearing a branched flexible unit with aggregation-induced emission enhancement characteristics

Precise molecular design of fluorinated tolane-based fluorophores can control both the electron density and molecular aggregated structures.

Halogen atom effect of fluorinated tolanes on their luminescence characteristics

Modification of the halogen constituent in the fluorinated tolane moiety is an effective method for tailoring the functionality of the material.