Search

The effects of silyl groups on the structural, absorption, fluorescence, and photoisomerization properties of stilbenes were investigated. In comparison to that of the parent stilbene (1), fluorescence quantum yields (Φf) of Me3Si‐substituted stilbenes 2–4 and 6 in solution were higher. Derivative 5, in which Me3Si groups are present at all ortho positions of the arene moieties, did not fluoresce at room temperature. The absorption and fluorescence wavelength maxima of Me3SiMe2Si‐substituted stilbene 7 occurred at longer wavelengths compared to those of the Me3Si analog 2. The results of theoretical calculations showed that this difference is a consequence of an increase in the HOMO energy of 7 caused by orbital interaction between π‐system and the σ(Si–Si) orbital. Stilbene 14, with two Me3Si‐C≡C groups at both para positions, had a high Φf (0.95). The calculated transition dipole moment (µ) was well correlated with Φf. Derivative 21, which contains Ph2N and Me3SiC≡C groups exhibited solvatofluorochromism because it possesses a twisted intramolecular charge transfer (TICT) excited state in which the Ph2N group and the aromatic ring are orthogonal. [ABSTRACT FROM AUTHOR]

We prepared amide-heterocycle (HC) compounds having various aromatic π-electron systems (Ar), such as phenyl, naphthyl, furyl, thienyl and phenanthryl moieties, and converted them as ligands to difluoroboronated complexes, Ar@HCs. Blue fluorescence from Ar@HCs was observed in solution and the solid state, and the fluorescence quantum yields (Φf) and lifetimes (τf) were determined. The Φf values in CHCl3 were as small as 0.1 except for the phenanthrene derivatives (0.4–0.6). Observation of the triplet–triplet absorption upon laser flash photolysis of Ar@HCs in solution indicated that the fluorescence process competes with intersystem crossing to the triplet state. Blue fluorescence in the solid state was observed with the Φf values of 0.3–0.7. Based on the crystallographic data, the relationship between the crystal structures and emission features of Ar@HCs in the solid state is discussed. [ABSTRACT FROM AUTHOR]

We prepared a variety of coumarin derivatives having expanded π-electron systems along the direction crossing the C3–C4 bond of the coumarin skeleton via a photochemical cyclization process and investigated their photophysical features as a function of the number (n) of the added benzene rings based on emission and transient absorption measurements. Upon increasing n, the fluorescence quantum yields of the π-extended coumarins increased. Expanding the π-electron system on the C3–C4 bond of the coumarin skeleton was found to be efficient for increasing the fluorescence ability more than that on the C7–C8 bond. Introducing the methoxy group at the 7-position was also efficient for enhancing the fluorescence quantum yield and rate of the expanded coumarins. The non-radiative process from the fluorescence state was not substantially influenced by the expanded π-electron system. The competitive process with the fluorescence was found to be intersystem crossing to the triplet state based on the observations of the triplet–triplet absorption. The effects of the expanded π-electron systems on the fluorescence ability were investigated with the aid of TD-DFT calculations. [ABSTRACT FROM AUTHOR]

[Display omitted] • Intramolecular multi-photocyclization of 1,3,5-tris(arylethenyl)benzenes was attempted in solution. • Successful preparation of star-burst-shaped polycyclic aromatic hydrocarbons was recognized by NMR spectroscopy. • Quantum yields and lifetimes of fluorescence of the star-burst compounds were determined in solution. • Photophysical features of the star-burst compounds were found to be similar irrespective of the number of the fused benzene rings. Photocyclization-oxidative aromatization sequence of diarylethenes, such as stilbene, is useful to construct π-expanded molecules, i.e. , phenacenes, having benzene rings fused in a zigzag manner. We applied this strategy to 1,3,5-tris(arylethenyl)benzene substrates, and successfully prepared polycyclic aromatic hydrocarbons with two-dimensionally expanded systems between the core benzene and the three fused-aromatic arms, what we call, star-burst aromatics. The photophysical features of the prepared star-burst-shaped molecules in solution were investigated with the aid of quantum chemical calculations. [ABSTRACT FROM AUTHOR]

Difluoroboronate β-diketones, compounds 1 having the fluorene moiety and the phenyl groups as well as the ligating precursors of the corresponding β-diketones, compounds 2 were synthesized. The photophysical features of compounds 1 were investigated based on the measurements of fluorescence yields and lifetimes, and transient absorption. Compounds 1 are significantly fluorescent with quantum yields of ca. 0.95 in acetonitrile and ca. 0.90 in chloroform. Fluorescence from compounds 1 was observed also in the solid state. Observation of extremely weak triplet–triplet absorption spectra of compounds 1 verifies the large fluorescence quantum yields. [ABSTRACT FROM AUTHOR]

[Display omitted] • Emission features of biaryls were investigated in solution and the solid state. • The fluorescence yields were greater than those of the original component molecules. • The positions for linking the chromophores affect the fluorescence yields. • Red-shifts in emission are due to overlapping of chromophores in the crystalline state. • The method of linking chromophores is applicable to developing efficient emitters in the solid state. Thanks to recent developments in spectrophotometric apparatuses, fluorescence quantum yields (Φ f) and lifetimes (τ f) of emissive compounds can be readily determined not only in solution but also in the solid state. In this work, we found that solid-state photoluminescence of biaryls consisting of naphthyl, phenanthryl and pyrenyl moieties emerged in the visible wavelength region at room temperature. The Φ f and τ f values of the studied biaryls were determined in the solid state as well as in solution. The biaryls showed fluorescence in the wavelength regions longer than that of the corresponding parent chromophores, i.e. , naphthalene, phenanthrene and pyrene, and the Φ f values in solution were greater than those of the parent ones. Some biaryls showed the solid-state emission spectra in the wavelength region longer than those in solution. Based on the crystallographic analysis results, relationship between the crystal packing and the emission features in the solid state was discussed. [ABSTRACT FROM AUTHOR]

• Compounds with multi N -methylaminoanthranyl (MANT) chromophores were prepared. • ･The MANT compounds showed blue fluorescence in solution and the solid state. • The fluorescence yields increased with increasing the number of the MANT chromophore. • The fluorescence rates in the solid state were found to be similar to those in solution. • The studied MANT compounds could be applicable to blue-color OLED. We prepared various compounds having the N -methylaminoanthranyl (MANT) moiety tethered with oligomethylene chains, and investigated the photophysical features in solution and the solid state based on the fluorescence quantum yields and lifetimes, and quantum chemical calculation. The molar absorption coefficient and fluorescence quantum yield were enhanced by an increase of the number of the MANT chromophore, resulting in an increase of the brightness as emission probes. Solid-state blue emission at room temperature was observed with moderate fluorescence quantum yields. The fluorescence rates in the solid state were found to be similar those in solution. From the results of the transient absorption measurements, the photophysical deactivation pathways in the solution were discussed. The studied multi-MANT compounds could be applicable to emissive photonic crystals and an exciton generating source for blue-color OLED. [ABSTRACT FROM AUTHOR]

• 7-Halogenated derivatives of 6-dimethylamino-2-phenylbenzothiazoles were prepared. • The halogenated derivatives have the deformed dimethylamino group by steric repulsion. • The halogenated derivatives showed blue-shifted electronic absorption and fluorescence. • Intersystem crossing from the fluorescence state suffers from heavy atom effect. 6-Dimethylamino-2-phenylbenzothiazole (1 -H) is a push-pull benzothiazole fluorophore mimicking the firefly oxyluciferin structure. We newly prepared 7-chloro and 7-bromo derivatives of 1 -H and its 4-acetyl derivative (2 -H), and their spectroscopic and photophysical properties were investigated. The halogenated derivatives showed the blue-shifted electronic absorption maxima and fluorescence emission maxima compared to 1 -H and 2 -H, resulted from the deformations of the NMe 2 groups and the electron withdrawing properties of the halogen groups. In addition, the halogen substitutions accelerate intersystem crossing by heavy atom effect, resulting in a decrease in fluorescence quantum yields. Interestingly, however, the halogenated derivatives of 2 -H still showed moderate fluorescence quantum yields. The halogenation effect is one of the guides to design push-pull benzothiazole fluorophores for tuning fluorescence properties. [ABSTRACT FROM AUTHOR]

6-Dimethylamino-2-phenylbenzothiazole ( 1a ) mimicking the firefly oxyluciferin structure and the derivatives with an electron-withdrawing substituent on the phenyl group were prepared, and their fluorescence properties were investigated in various solvents. 1a showed solvatochromic fluorescence with good fluorescence quantum yields ( Φ f >0.8). The introduction of an electron-withdrawing group led to a red-shift of the emission maximum. In particular, the derivatives with the 2,2-dicyanoethenyl and (1,3-dihydro-1,3-dioxo-2 H -inden-2-ylidene)methyl groups showed near-infrared fluorescence in chloroform. In addition, the derivative with the phenylimine moiety showed efficient solid-state fluorescence, resulted from a molecular arrangement inhibiting intermolecular interactions for quenching the fluorescence state in crystals. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Push-pull benzothiazole derivatives were designed based on firefly oxyluciferin. • The derivatives show solvatochromic fluorescence with high quantum yields. • Solid state fluorescence of the derivatives were depended on the crystal structures. Abstract 6-Dimethylamino-2-phenylbenzothiazoles with a carboxy, ester and amide substituent on the 2-phenyl group were prepared as a series of the push-pull benzothiazoles, and their spectroscopic and photophysical properties in solutions were investigated. The derivatives showed solvatochromic fluorescence with quantum yields over 0.68 in various organic solvents similar to the core fluorophore structure. The color variation ranges in fluorescence solvatochromism of the derivatives were wider than that of the original compound having the core structure, 6-dimethylamino-2-phenylbenzothiazole. It was also found that the derivatives together with the original compound show solid state fluorescence depending on their crystal structures. In particular, an ester derivative with a protected serine has a reasonable crystal packing leading to increase in fluorescence efficiency. The results of the present study provide a guide to design push-pull 2-phenylbenzothiazoles exhibiting fluorescence in solution and the solid state. [ABSTRACT FROM AUTHOR]