Fluorescence Quantum Yields Of Compounds Research Articles

Substituent Effects on Selective Syntheses of Fused‐Ring Heterocycles Based on Carbazole and Naphthalene by Photocyclization: Synthesis, Crystal Structures, and Properties

AbstractTwo new different types of fused‐ring heterocycles based on the carbazole and naphthalene, that is, 10‐bromine‐7‐hexyl‐7‐monoaza[6]helicene (7) and 14‐hexyl‐11‐(thiophen‐2‐yl)‐14H‐phenanthro[4, 3‐b]carbazole (10) were successfully synthesized through the introduction of bromine and thiophene subtituents into 9‐Hexyl‐9‐carbazole‐3‐carbaldehyde. Their structures were fully characterized by 1H NMR, 13C NMR, mass spectroscopy and single‐crystal X‐ray diffraction pattern. Single‐crystal structures revealed that compound 10 possessed less distortion and deformation, and better planarity than compound 7. Compounds 7 and 10 had good solubility and thermal stability (Td = 236.82 °C for 7, Td = 214.96 °C for 10). These compounds had absorption maximum peaks at 319 nm for 7, 337 nm for 10, and emitted blue light with the peaks at 435 nm for 7, 447 nm for 10 in dichloromethane. The fluorescence quantum yields of compounds 7, 10 in different solvents were measured in the range of 8% ‐ 18%, 35% ‐ 74%, respectively. These results showed that introducing the functional substituent group of thiophene to the carbazole could not only transform photocyclization products from helicenes into other types of fused‐ring heterocyclic compounds but also increase the fluorescence quantum yields of compound 10 by more than three and half times. The simple synthetic method would pave the way for obtaining fused‐ring heterocycles with diverse types and various properties.

Tunable Dual Fluorescence of 3‐(2,2′‐Bipyridyl)‐Substituted Iminocoumarin

3-(2,2'-Bipyridyl)-substituted iminocoumarin molecules (compounds 1 and 2) exhibit dual fluorescence. Each molecule has one electron donor and two electron acceptors that are in conjugation, which leads to fluorescence from two independent charge transfer (CT) states. To account for the dual fluorescence, we subscribe to a kinetic model in which both CT states form after rapid decays from the directly accessed S(1) and S(2) excited states. Due to the slow internal conversion from S(2) to S(1), or more likely the slow interconversion between the two subsequently formed CT states, dual emission is allowed to occur. This hypothesis is supported by the following evidence: 1) the emission at short and long ends of the spectrum originates from two different excitation spectra, which eliminates the possibility that dual emission occurs after an adiabatic reaction at the S(1) level. 2) The fluorescence quantum yield of compound 2 grows with increasing excitation wavelength, which indicates that the high-energy excitation elevates the molecule to a weakly emissive state that does not internally convert to the low-energy, highly emissive state. The intensity of the two emission bands of 1 is tunable through the specific interactions between either of the two electron acceptors with another species, such as Zn(2+) in the current demonstration. Therefore, the development of ratiometric fluorescent indicators based on the dual-emitting iminocoumarin system is conceivable. Further fundamental studies on this series of compounds using time-resolved spectroscopic techniques, and explorations of their applications will be carried out in the near future.

Two-Photon Excitation of Substituted Enediynes

Electronic spectroscopy of nine benzannelated enediynes and a related fulvene was studied under one-photon and two-photon excitation conditions. We utilize measured absorbance and emission spectra and time-resolved fluorescence decays of these molecules to calculate their radiative lifetimes and fluorescence quantum yields. The fluorescence quantum yields for the other compounds were referenced to the fluorescence quantum yield of compound 3 and used to determine relative two-photon absorption cross-sections. Further insight into experimental studies has been achieved using time-dependent density functional (TD-DFT) computations. The probability of two-photon absorption (TPA) increases noticeably for excitation to the higher excited states. The photophysical properties of benzannelated enediynes are sensitive to substitutions at both the core and the periphery of the enediyne chromophore. Considerably enhanced two-photon absorption is observed in an enediyne with donor substitution in the middle and acceptor substitution at the termini. Excited states with B symmetry are not active in TPA spectra. From a practical point of view, this study extends the range of wavelengths applicable for activation of the enediyne moiety from 350 to 600 nm and provides a rational basis for future studies in this field. Our theoretical computations confirmed that lowest energy TPA in benzannelated enediynes involves different orbitals than lowest energy one-photon absorbance and provided further support to the notion that introduction of donor and acceptor substituents at different ends of a molecule increases TPA.

Ortho-Fused Heterocyclic Derivatives as Efficient Electroluminescent Materials

Abstract We describe the synthesis and optical properties of 1,2-dithienylethylene derivatives (DTE-8–15) consisting of ortho-fused heterocyclic systems such as benzodithiophene and naphthothiophene. The compounds 8–13 are highly fluorescent in toluene solution and their intensities are approximately two times as large as 4,4′-bis(2,2-diphenylethenyl)biphenyl (18). The fluorescence quantum yields of compounds 8–15, except for 14, are 2 times as high as that of 18. Although a maximum luminance of 9 in a multilayer device of structure ITO/CuPc/NPD/9/Alq3/LiF/Al is low (186 cd m-2), the brightness is significantly improved by doping the host emitters such as 18 and 9,10-bis(2-biphenylyl)-2-(t-butyl)anthracene (19) with 9. The electroluminescent (EL) device doped with 8 (5%) in the layer of 19 exhibits blue emission with a maximum luminance of 30000 cd m-2 at a driving voltage of 14 V and a luminous efficiency of 2.42 lm W-1 at 5V.

Syntheses, structures, and electroluminescence of new blue luminescent star-shaped compounds based on 1,3,5-triazine and 1,3,5-trisubstituted benzene

Four novel blue luminescent star-shaped compounds 1,3,5-tris(di-2-pyridylamino)benzene, 1, 1,3,5-tris[p-(di-2-pyridylamino)phenyl]benzene, 2, 2,4,6-tris(di-2-pyridylamino)-1,3,5-triazine, 3, and 2,4,6-tris[p-(di-2-pyridylamino)phenyl]-1,3,5-triazine, 4, have been synthesized and fully characterized. Compounds 1, 2 and 4 were prepared from the reactions of appropriate s-triazine and 1,3,5-trisubstituted benzene compounds with di-2-pyridylamine via copper-mediated Ullmann condensation in good yield (45–85%). Compounds 1, 2 and 4 show glass formation. Compounds 1–4 emit a blue color both in solution and in the solid state. The emission maxima of compounds 1–4 in the solid state are at λ = 412, 409, 393 and 440 nm, respectively. Fluorescence quantum yields of compounds 1–4 are 0.53, 0.16, 0.43 and 0.78, respectively. Electroluminescent devices using compounds 1–4 as the emitters were fabricated.

SYNTHESIS AND SPECTROSCOPIC CHARACTERIZATION OF WATER SOLUBLE PERYLENE TETRACARBOXYLIC DIIMIDE DERIVATIVES

Two new perylene dye, N,N′ bis(4-hydroxyphenyl)-3,4,9,10 perylenebis (dicarboximide) (1) and N,N′-bis-(3,3,5,5-tetramethyl piperidine)-3,4,9,10-perylenebis (dicarboximide) (2) have been synthesized. They are both soluble in water. A limited number of water soluble perylene dyes published in literature have been obtained in pure grade only with column chromatography. For this reason they are not useful for certain applications. The N, N′-bis-(3,3,5,5-tetramethyl piperidine)-3,4,9,10-perylenebis (dicarboximide) derivative is obtained in high purity with high yield. Solubility of dyes, (1) and (2) were measured as 4.4 × 10−5 g/ml and 5.1 × 10−3 g/ml respectively in distilled water at pH: 7. The solubility of N.N′-bis- (3,3,5,5-tetramethyl piperidine)-3,4,9,10-perylenebis (dicarboximide) was increased with decreasing pH. The chemical and photochemical stabilities of 1, and 2 are very high. The fluorescence quantum yields of compounds are different (0.053 (1), 0.110 (2)). The report includes the electronic absorption and emission spectra, extinction coefficients and fluorescence quantum yields.

A study of the photophysical properties of 2,4,6-triphenyl pyrylium salts with rigid and non-rigid structures

The photophysical properties of 2,4,6-triphenyl pyrylium salts with rigid and non-rigid structures were investigated. It was found that the polarizability of compound 2 (with a rigid structure) was stronger than that of compound 1 (with a non-rigid structure) in the excited state. The fluorescence quantum yield of compound 1 increased slightly with increasing viscosity of the solvent, while the fluorescence quantum yield of compound 2 decreased dramatically in the same conditions. It was also discovered that the hindered rotation of the 4-phenyl group in the molecules of 2,4,6-triphenyl pyrylium salts inhibits the fluorescence emission of these compounds.