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]

Spectroscopic and photophysical properties of firefly luciferin and oxyluciferin analogues with an amine substituent ( NH2, NHMe and NMe2) at the C6' position were studied based on absorption and fluorescence measurements. Their π-electronic properties were investigated by DFT and TD- DFT calculations. These compounds showed fluorescence solvatochromism with good quantum yields. An increase in the electron-donating strength of the substituent led to the bathochromic shift of the fluorescence maximum. The fluorescence maxima of the luciferin analogues and the corresponding oxyluciferin analogues in a solvent were well correlated with each other. Based on the obtained data, the polarity of a luciferase active site was explained. As a result, the maximum wavelength of bioluminescence for a luciferin analogue was readily predicted by measuring the photoluminescence of the luciferin analogue in place of that of the corresponding oxyluciferin analogue. [ABSTRACT FROM AUTHOR]

Based on spectroscopic measurements and DFT calculations, fluorescence properties of thiazolo[4,5-b]pyrazine (TPy) derivatives with the phenyl group at the C2 position were studied. TPys were readily prepared from the corresponding amidopyrazines, which have a similar fluorescent core to a bioluminescence light emitter, Cypridina oxyluciferin. It was found that the introduction of electron-donating (methoxy and dimethylamino) groups onto the 2-phenyl moiety of the TPy derivatives, as well as the phenyl and 4-(dimethylamino)phenyl groups at C2 and C6, respectively, increases the fluorescence yield and appearance of solvatochromic character. The mechanism of increasing the fluorescence yield depending on the substituents is discussed. These findings provide useful information on designing new TPy fluorophores. [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]

Boron difluoride (BF 2 ) complexes of N -(5-phenyl-2-pyrazinyl)pivalamide and its derivatives having a substituent on the phenyl group were prepared and their spectroscopic properties were investigated. It was found that the BF 2 complexes show fluorescence in solution and the solid state. The origins of the fluorescence properties are discussed on the basis of the fluorescence yields and lifetimes, crystal structures and DFT calculations. The present work would provide a guide to design BF 2 complexes of amidopyrazines exhibiting solid state fluorescence. [ABSTRACT FROM AUTHOR]