Two-photon induced blue fluorescent emission of heterocycle-based organic molecule

LED based on alternating benzene-furan oligomers

A series of conjugated-chain compounds which contain two furan units and more than three other aromatic ring units were synthesized by two different methods, their UV-visible absorption coefficient (ε), maximum absorption wavelengths (λa), fluorescence emission wavelengths (λe), stokes shift and quantum yields (Φ) were determined, the relationships between the molecular structures and the effects of spectral behaviors were discussed. Meanwhile, the excitation spectrum and emission spectrum of 2b and 2d in solid and in ethyl acetate were respectively recorded, the thermal stability of 2b and 2d was evaluated, and the fluorescence emission behaviors of two light emitting diodes, fabricated with 2b and 2d as phosphors, were investigated. The results showed that most of target compounds can perform high fluorescence emission ability, compounds 2b and 2d can perform higher thermal stability under 350°C and they are suitable for making light emitting diode as phosphors, the light emitting diodes fabricated with 2b and 2d can show higher fluorescence emission ability. Therefore, those compounds are worthy of further being developed as fluorescent emission materials.

Concise synthesis and two-photon-excited deep-blue emission of 1,8-diazapyrenes

Efficient violet-blue-emitting molecules are especially useful for applications in full-color displays, solid-state lighting, as well as in two-photon absorption (TPA) excited frequency-upconverted violet-blue lasing. However, the reported violet-blue-emitting molecules generally possess small TPA cross sections. In this work, new 1,8-diazapyrenes derivatives 3 with blue two-photon-excited fluorescence emission were concisely synthesized by the coupling reaction of readily available 1,4-naphthoquinone O,O-diacetyl dioxime (1) with internal alkynes 2 under the [{RhCl(2)Cp*}(2)]-Cu(OAc)(2) (Cp*=pentamethylcyclopentadienyl ligand) bimetallic catalytic system. Elongation of the π-conjugated length of 1,8-diazapyrenes 3 led to the increase of TPA cross sections without the expense of a redshift of the emission wavelength, probably due to the rigid planar structure of chromophores. It is especially noteworthy that 2,3,6,7-tetra(4-bromophenyl)-1,8-diazapyrene (3c) has a larger TPA cross section than those of other molecules reported so far. These experimental results are explained in terms of the effects of extension of the π-conjugated system, intramolecular charge transfer, and reduced detuning energy.

Synthesis of benzimidazoles containing pyrazole group and quantum chemistry calculation of their spectroscopic properties and electronic structure

Five benzimidazole compounds containing pyrazole group were synthesized via one-step reaction of o-phenylenediamine and 1-arylpyrazole-4-carbaldehyde in ethanol under mild conditions. The composition and structure of resultant benzimidazole compounds were analyzed by means of elemental analysis, mass spectrometry, (1)H-nuclear magnetic resonance spectroscopy and X-ray single crystal diffraction. The ultraviolet-visible light spectra and fluorescent spectra of the products were measured. Their ground-state (S(0)) equilibrium geometries and vibrational frequencies were determined based on B3LYP method, and their first excited-state (S(1)) geometries were fully optimized based on 6-31G (d, p) basis set of TD-B3LYP method. Besides, the spectroscopic properties of the products were computed based on cc-pVTZ basis set of TD-B3LYP method and compared with corresponding experimental data. It has been found that benzimidazole compounds containing pyrazole group can be readily synthesized in a high yield via one-step reaction of o-phenylenediamine and 1-arylpyrazole-4-carbaldehyde in ethanol solvent. The fluorescence properties of the five synthesized compounds are closely related to their molecular structure; and their computed fluorescence spectra well correspond to their experimental values. Moreover, they have stable structure and strong fluorescence, showing potential application in time-resolved fluoroimmunoassay and DNA probe.

Synthesis and optical behaviors of 2-(9-phenanthrenyl)-, 2-(9-anthryl)-, and 2-(1-pyrenyl)-1-alkylimidazole homologues

Eight 2-(9-phenanthrenyl)-, 2-(9-anthryl)- and 2-(1-pyrenyl)-1-alkyl-benzimidazole compounds, three 2-(9-anthryl)-1-alkylphenanthroimidazole compounds and five 4,5-diphenyl-1-alkyl-2-(9-anthryl)imidazole compounds were synthesized by alkylation reactions of the corresponding benzimidazole, phenanthroimidazole or imidazole compounds. 2-(10-Bromo-9-anthryl)-1-alkyl-benzimidazole compounds were prepared by bromination reaction of 2-(9-anthryl)-1-alkylbenzimidazole compounds. All the synthesized compounds were characterized by elemental analysis, (1)H NMR, (13)C NMR, MS or HRMS; their absorption coefficients (epsilon), maximum absorption lambda(amax), fluorescence emission maximum lambda(em), Stokes shifts and fluorescence quantum yields (Phi(F)) in ethyl acetate were determined; their fluorescent lifetimes (T(1) and T(2)) were measured in ethyl acetate and in solid state, respectively. The crystal structure of 2-(9-anthryl)-1-n-butyl-4,5-diphenylimidazole (12a) was determined to be triclinic, space group P-1 types, using single crystal X-ray crystallography technique. The results showed that these compounds exhibited moderate fluorescence-emission abilities and higher solubility in most organic solvents than their corresponding starting materials. The relationships between the optical behaviors and structures for these compounds were discussed.

Optical behaviors of conjugated-chain compounds containing benzene and furan units

Thirteen conjugated-chain compounds which contain benzene and furan units were prepared, their optical behaviors, including UV-vis absorption coefficient (epsilon), absorption wavelengths (lambdaa), fluorescence emission wavelengths (lambdae), and quantum yields (Phi) were measured. Meanwhile, their LUMO and HOMO energy were determined by cyclic voltammetry and their second-order polarizations (betaxxx) values were determined by solvatochromic method, respectively. The results showed that this kind of compounds possess a shorter lambdaa (320-365 nm) and performance a higher Phi values, especially for 2aa, 2ab, 2ac and 2bb, their Phi values are all more than 90%. These compounds, except 2db, showed a higher betaxxx values in DMSO, especially for 2dc (75.77x10(-30) m5 C-1) and 2dd (83.32x10(-30) m5 C-1), than that 10-methyl-acridone (6.578x10(-30) m5 C-1) or 10-benzylacridone (6.845x10(-30) m5 C-1) in DMSO did, and second harmonic generation value of 10-methylacridone and 10-benzylacridone in powder are, respectively, 1.381 and 1.861 times of that value of urea. The betaxxx values and Phi values determined for these compounds in this work were lower than these values which were desired in the original work, this phenomena was explained from their molecular structures. This work confirmed that as these compounds performance shorter lambdaa and higher Phi values, they could be good blue-color optical materials for some fields, such as OLED materials, two-photo absorption materials, fluorescent dyes.

Study on the second-order optical behavior of 4-(substituted-benzylidene)-2-phenyl-4H-oxazol-5-one

The maximum absorption wavelengths (lambda(a-max)), absorption coefficient (epsilon), maximum emission wavelengths (lambda(e-max)) of 4-benzo[1,3]dioxol-5-ylmethylene-2-phenyl-4H-oxazol-5-one (1), 4-(3,4-dimethoxybenzylidene)-2-phenyl-4H-oxazol-5-one (2) and 4-(3,4,5-trimethoxy-benzylidene)-2-phenyl-4H-oxazol-5-one (3) were measured, their second-order nonlinear polarization values (beta(xxx)) were determined by solvatochromic method. Although the spectral nature (lambda(a-max), epsilon, lambda(e-max)) and beta(xxx) values of 1, 2 and 3 were close to each other in the same solvent, the second-order harmonic generation (SHG) value of sample 1 is higher obviously than that of sample 2 or 3 in solid state. The crystal structures of 1 and 2 characterized by single crystal X-ray diffraction technique indicated the reason why the SHG value of 1 is higher.