低聚芴及其衍生物吸收和发射光谱性质的量子化学研究

Quantum Chemical Studies of Absorption and Emission SpectrocopicProperties for Oglimeric Fluorenes and Its Derivatives

用 DFT/ B3 LYP方法对低聚物 ( PF) 2 n和 ( PFDBO) n( n=1— 4)体系进行了全优化 ,计算得到两个系列低聚物的电离能 PI( v,a)、电子亲和势 EA( v,a)、空穴抽取能 EHP和电子抽取能 EEP等相关能量 ,并用 ZINDO和 TD-DFT方法计算其吸收光谱 ,分析了两系列总能量和 HOMO-LUMO能隙随 n递增的变化规律及对低聚物稳定性和光谱性质的影响 ,推断高聚物的发光性质 .用 CIS方法优化低聚物的 S1激发态结构并分析其与发射光谱的关系 .计算结果表明 ,这两个系列低聚物激发态结构中都有使所有骨架原子共平面的趋势 .由于插入 CH2 OCH2 ,使 PFDBO的七元环部分发生较大的扭曲 (两个苯环间成 42 .5°± 0 .5°的二面角 ) ,致使有效共轭链被破坏、能带带隙变宽、吸收发射光谱波长变短 .

We have fully optimized the structures of the oligomers of (PF) 2n and (PFDBO) n (n=1—4) using DFT/B3LYP method and calculated their P I(v,a), E A(v,a), E HP , E EP . The absorption spectra data were calculated at ZINDO and TD-DFT levels of theory. We analyzed the rules to the variation of their HOMO-LUMO energy gap with n rising and how the energy gap reflected the spectral properties of the oligomers to deduce the spectral properties of their polymers. We optimized the S 1 excited geometries and studied the emission spectra. Moreover, in the excited geometries all the framework atoms in a molecule are apt to coplanar. Above all, the dramatically twisted segment of seven-membered-ring in PFDBO(dihedral angel between it′s two phenyl ring is 42.5°±0.5°), because of CH 2OCH 2 caused the conjugated backbone broken. So the energy gap of it is broader, which makes in the max absorption and emission wavelengths of PFDBO shorter than PF′s.