Theoretical Study On Intramolecular Charge Transfer Of O-fluoroazobenzenes Photoswitches

In this information age, due to vast amounts of information storage，opticalinformation storage materials are in urgent demand. As a new type of photochromiccompounds, azobenzene with excellent optical and photochromic cis-transisomerization characteristics has been widely used in many fields such as biologicalmaterials and information materials and become the favorite in optical informationstorage materials.However, the azobenzene itself has two drawbacks that can not be ignored.One is the use of UV light to induce anti-cis isomer, by*excitation, whichpotentially brought impact and damage to the surrounding environment. Another isnot fully reversible cis-trans isomerization, which needed to be induced in thevisible region, where then*band of the cis and trans isomers were oftenignored. Therefore after back-switching, the PSSs for the E (trans) isomer couldn’tbe given. These drawbacks can be avoided by changing the chemical structure ofazobenzene, In order to eliminate these drawbacks, we can adjust the chemicalstructure of the azobenzene compounds. Meanwhile, The physical and chemicalproperties of it will be improved.In this paper, the o-Fluoroazobenzene was synthesized by commercially2,6-difluoroaniline in one step. Then we got compounds1and2by introducingeither electron-donating group (EDGs) N-acyl or electron-withdrawing group(EWGs)ester to the para-positions of the o-Fluoroazobenzene that can help to adjustthe spectral characteristics and maximize the absorption and the gap betweenthen*band. For compound1, the N-acyl groups work as the donor and theo-fluoroazobenzene is the acceptor. And for compound2, o-fluoroazobenzene is thedonor, the ester groups work as the acceptor. All of the calculations reported in thispaper were carried out by the quantum chemistry methods. The ground-stategeometries of compound1and2were optimized with density functional theory (DFT),using B3LYP functional and DZVP basis set. The properties of the excitedstates were investigated with time-dependent density functional theory. The HOMOand LUMO orbitals and the corresponding methods were listed. The absorptionpeaks of the E and Z isomers of compound1were403.18nm fromHOMOâ†'LUMO and329.84nm from HOMO-1â†'LUMO respectively. Those forcompound2were371.65nm from HOMO-1â†'LUMO and468.66nm fromHOMO-4â†'LOMO. Furthermore, we adopted UV spectrum and circular dichroismspectrum to get a better analysis of the excited states properties of compound1and2. The three dimensional (3D) cube representations were applied to visualize theprocess of charge transfer. The transition density reveals the orientation andoscillator strengths of the dipole moment. The charge difference density shows theresults of the intramolecular charge transfer. The atomic resolved DOS was appliedto find out if there was density on the HOMOs or LUMOs. We envisioned twodimensional cube representation (2D) were using to visualize the electron-holecoherence and the electron delocalization. The results were consistent with theanalysis by3D methods.