Propeller-shaped molecules diphenyldibenzofulvene (1) and (4-methoxyphenyl)phenyldibenzofulvene (2) were nonemissive when dissolved in good solvents but became luminescent when aggregated in poor solvents or in the solid state, showing a novel phenomenon of aggregation-induced emission (AIE). 8-Phenylbenzo[e]acephenanthrylene (3), a ring-closed form of 1 with one of its phenyl blades locked, was emissive in the solutions, suggesting that the AIE effects of 1 and 2 are caused by the restrictions of intramolecular rotations of their aromatic blades in the aggregation state. The crystals of 1 and 2 emitted stronger, bluer lights than their amorphous powders, possibly due to the structural rigidification and conformational twisting of the dye molecules in the crystalline phase. The light-emitting diodes with a device configuration of ITO/NPB/dye/BCP/Alq3/LiF/Al were fabricated, which emitted bluish-green and yellow lights with maximum luminance and current efficiency up to 5000 Cd/m2 and 1.90 Cd/A, respectively.

Aggregation-Induced Emission: Effects of Molecular Structure, Solid-State Conformation, and Morphological Packing Arrangement on Light-Emitting Behaviors of Diphenyldibenzofulvene Derivatives

Experimental and CIS, TD-DFT, ab initio calculations of visible spectra and the vibrational frequencies of sulfonyl azide-azoic dyes.

Extensive TD-DFT investigation of the first electronic transition in substituted azobenzenes

Using an ab intio TD-DFT approach systematically accounting for the molecular surroundings effects, we have computed the n → π* absorption wavelength of 22 azoalkane derivatives. For the complete set of molecules, we propose a theoretical procedure able to reproduce the major auxochromic effects, and to deliver a mean absolute error of 5.8 nm (0.056 eV) with maximal deviations limited to 21 nm (0.20 eV). The impact of including in the model explicit solvent molecules is discussed as well. This contribution confirms that PCM-TD-PBE0 is a first-grade method for simulating the vertical absorption spectra of organic dyes.

On the TD-DFT UV/vis spectra accuracy: the azoalkanes

Using time-dependent density functional theory and the polarizable continuum model, we have simulated the absorption spectra of an extended series of azobenzene dyes. First, we have determined a theoretical level optimal for this important class of dyes, and it turned out that a C-PCM-CAM-B3LYP/6-311+G(d,p)//C-PCM-B3LYP/6-311G(d,p) approach represents an effective compromise between chemical accuracy and computational cost. In a second stage, we have compared the theoretical and experimental transition energies for 46 n π☆ and 141 π π☆ excitations. For the full set, that spans over a 302–565 nm domain, we obtained a mean absolute deviation of 13 nm (0.10 eV) and a linear correlation coefficient of 0.95, illustrating the accuracy of our approach, though some significant outliers pertained. In a last step, the impact of several modifications, that is, trans/cis isomerization, variation of the acidity of the medium and azo/hydrazo tautomerism have been modeled with two functionals. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

Absorption spectra of azobenzenes simulated with time-dependent density functional theory

In order to predict the absorption half-band width, the ground state and the first singlet-excited state configurations of some azobenzene compounds are calculated by B3LYP/6-311G* and CIS methods, respectively. Based on the configurations obtained above, the absorption maximum and emission maximum are calculated by TD-DFT method, the results are in good agreement with observed values. Further study shows a linear relationship between Δ λ 1/2 (the observed absorption half-band width) and S (the difference between the emission maximum and absorption maximum). According to the relationship obtained, the absorption half-band width of other azobenzene derivatives in the same series could be predicted successfully.

Research on the prediction of absorption half-band width of some azobenzene compounds

The optimized geometry and electronic absorption spectrum of cyanine compounds were calculated by semi-empirical PM3 and ZINDO/S method in HyperChem 7, the results show that based on the optimized geometry obtained from PM3 method, the electronic absorption spectrum of cyanine compounds could be predicted precisely by setting OWFπ–π (one of the adjustable parameters in ZINDO/S method) at an appropriate value. It is found that there is an excellent linear relationship between OWFπ–π and n (the number of conjugated double-bonds within the conjugated chain) exists, the value of OWFπ–π decreases as n increases. At the same time, the research on molecular orbital indicates that the maximum absorption wavelength of cyanine compounds originates from the electron transition from HOMO to LUMO, a transition enhances the bonding of central carbon-atom with neighboring atoms when n is an odd number while weakens the bonding of central carbon-atom with neighboring atoms when n is an even number.

Shenfeng Yuan

Papers

Research on the prediction of absorption half-band width of some azobenzene compounds

Study on the prediction of electronic absorption spectrum for cyanine compounds