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Investigation on Structures and Nonlinear Optical Properties of PPV and Its Derivatives Systems with Adsorbing Alkali Metal Atom

By means of the density functional theory(DFT) method,we investigated detailedly the structures and nonlinear optical(NLO) properties of the adsorbed phenylenevinylene(PPV) polymer with the alkali metal Li atom and its corresponding derivatives systems decorated with the donor/acceptor group.In these PPVbased systems,the Li atom can be adsorbed stably on the surfaces of PPV and its derivatives,as revealed by their considerable adsorption energies(62.3—78.2 k J/mol).It is revealed that when adsorbing the Li atom on the [PPV]n(n = 2—4),the evident charge transfer can occur between them,and this effect of lithium salt can effectively enhance the first hyperpolarizabilities β0values of PPV systems from original 249—756 a.u.to the range of 1.16 × 104—1.37 × 105 a.u.Comparatively,when adsorbing the alkali metal Li atom on the PPV derivatives modified with only donor(—NH2) or acceptor(—CN) group,the first hyperpolarizabilities of systems can be significantly improved further,where the β0values of Li@ [NH2-(PPV)4]and Li@ [(PPV)4-CN] can be as large as 1.61 × 105 and 2.85 × 105 a.u.,respectively.This can be attributed to the case that the cooperation effect of lithium salt and Donor-π-Acceptor can result in the more evident decrease of main transition energy of system.Further,this cooperation effect can be strengthened significantly in the Li-adsorbed PPV derivatives decorated with donor/acceptor(—NH2/ —CN) pairs,which can lead to the more effective improvement of β0value(up to 3.56 × 105 a.u.at n = 4).This work can provide some new valuable insights for designing the new type of high-performance NLO materials based on the excellent PPV systems.