Theoretical Studies On The Effects Of Steric Hindrance On Molecular Conformation And Spectrum Of Organic Luminescent Molecules

Research on design, synthesis and performance of organic luminescent moleculedeveloped rapidly in recent years. Theoretic calculation can offer the relation betweenmolecular structure and performance which to offer theoretical basis for molecular design.Therefore, theoretic forecasting organic luminescent molecular with excellence photoelectricperformance was the important component parts for organic luminescent molecule furtherresearch development. In this paper, we researched the effects of steric hindrance onmolecular conformation of several kinds organic luminescent molecule.Triphenyl imidazole compounds also named lophine, Those compounds not only haveexcellence nonlinear optical performance, transparency and stability, but also two-photonabsorbing compounds. The structures of four lophine derivatives have been optimized atDFT/B3LYP//6-31G*method. Based on the obtained stable molecular configuration, wecalculated electric structure and adopted the finite field (FF) method to analyze thesecond-order nonlinear optical (NLO) properties. Time dependent density functional theory(TD-DFT) methods were employed to calculate absorption spectra of these molecules. Theresults show that planar conjugation has been changed and the total virtual value ofsecond-order polarizability (βtot) reduced by introducing a benzyl in3-imidazole and a nitro in4,5-pyridine ring to lophine. The two groups induce blue-shift in the absorption spectra. Also,it is found that the λmaxof a and c are mainly from the Ï€â†'Ï€*electronic transition of HOMOâ†'LUMO in CH2Cl2, The λmaxof b and d are mainly from the Ï€â†'Ï€*electronic transition ofHOMOâ†'LUMO+2in CH2Cl2.4-Amino-1,8-Naphthalimide(ANI) are widely used organic photoelectric material due toexcellence optical performance, In this text, the geometry of the ground state of ANIderivatives was optimized by B3LYP approaches at6-31+G(d)basis sets. Based on theobtained stable molecular configuration, the absorption spectra were calculated byTD-B3LYP/6-31+G(d) method. With the help of CIS/6-31+G(d), the geometry of the firstexcited state(S1) was calculated. Based on the obtained stable excited state configuration, thefluorescence spectra were calculated by TD-DFT/MPWK/6-31+G(d) method. The resultsshow that an increase in the length of the dialkyl groups connected to the amino nitrogen andan increase in the size of the ring containing the amino nitrogen enhances electron donor inductive effect and the torsion angle which between naphthalimide planar and the dialkylgroups; The energy gap was reduced. Red-shift in the calculated absorption maxima andemission maxima by an increase in the polarity of the media. The effect of the polarity of themedium on the fluorescence maximum is more pronounced than that on the absorptionmaximum.