【摘要】 采用密度泛函理论(DFT)-B3LYP/6-31G(d)方法研究了给、吸电子基团对称和不对称封端对9,9’-螺双芴光电性质的影响.全优化得到了9,9’-螺双芴封端前后各分子的稳定构型,分析了各种封端系列的HOMO-LUMO能隙.结果表明,以给电子基团噻吩和吸电子基团噁二唑不对称封端作用于9,9’-螺双芴,能使LUMO能量大幅降低,HOMO能量略有升高,能隙明显变窄.不对称封端低聚9,9’-螺双芴分子[T(SBF)nO,n=1～4]在相同计算水平下的全优化结果表明吸、给电子基团的电荷比随n的增大而递增,揭示了给、吸电子基团间存在分子内电荷转移(ICT),且这种电荷转移在低聚物中得到加强.计算得到的电离势、电子亲和势、空穴抽取能、电子抽取能和重组能等相关能量,证明了在主链上形成的载流子传输通道提高了空穴和电子传输的能力.用TD-DFT和ZINDO方法计算了T(SBF)nO(n=1～4)的吸收光谱,随着n的增大而激发光所需的能量减小,光谱红移,吸收强度增大;用CIS/6-31G(d)方法优化得到了不对称封端9,9’-螺双芴S1激发态构型,结果表明,激发态的平面化程度比基态高.更多还原

【Abstract】 Symmetrical and asymmetrical end capped 9,9’-spirobifluorene with electron donor or/and acceptor groups are calculated to investigate the influence of the end-capping groups by using DFT/B3LYP method at 6-31G(d) level.We fully optimize all the structures concerned.Analyzing the HOMO and LUMO energy levels and HOMO-LUMO gaps of all species,we find that the LUMO level drops while the HOMO level slightly increases and therefore the HOMO-LUMO gap shrinks when 9,9’-spirobifluorene is asymmetrically end-capped by an electron donor group oxadiazole (O) and an electron acceptor group thiophene (T).Full optimizations,at the same B3LYP/6-31G(d) level,on the structures of the oligo-9,9’-spirobifluorene end-capped with thiophene and oxadiazole [T(SBF)nO,n=1～4] show that the ratio of the partial charge of the donor group over that of the acceptor group grows larger with increasing chain length n.The donor and acceptor moieties exhibit intramolecular charge transfer (ICT) and the charge transfer gets enhanced in oligomers.The ionization potentials (IPs),electron affinities (EAs),hole extraction potentials (HEP),electron extraction potentials (EEP) and the reorganization energies (λ) are calculated to show that the charge carrier injection from donor to acceptor group further facilitates the transport of both electrons and holes.Absorption spectra of T(SBF)nO (n=1～4) are obtained by employing TD-DFT and ZINDO calculations.The results show that,with increasing chain length n,the excitation energy becomes smaller,the spectra are red-shifted,and the oscillator strength is enhanced.The singlet excited geometry of T(SBF)1O is calculated using the single-excitation configuration interaction CIS method at the same 6-31G(d) level.Compared to the ground state,the excited state tends to move toward a planar geometry.更多还原