Nonlinear optical properties of rhenium(I) complexes: Influence of the extended π-conjugated connectors and proton abstraction

• Deprotonation affect causes an efficient second-order NLO switching.
• Deprotonation has an influence on the βvec sign from positive to negative.
• The differences on NLO properties are due to a change in charge transfer pattern.
• The absorption bands of all complexes show deprotonation dependence.

The photoinduced proton-coupled electron transfer chemistry is very crucial to the development of nonlinear optical (NLO) materials with large first hyperpolarizability contrast. We have performed a systematic investigation on the geometric structures, NLO switching, and simulated absorption spectra of rhenium(I) complexes via density functional theory (DFT). The results show that the first hyperpolarizabilities (βvec) increase remarkably with further extending of the organic connectors. In addition, the solvent leads to a slight enhancement of the hyperpolarizability and frequency dependent hyperpolarizability. Furthermore, the proton abstraction plays an important role in tuning the second-order NLO response. It is found that deprotonation not only increases the absolute value of βvec but also changes the sign of βvec from positive to negative. This different sign can be explained by the opposite dipole moments. The efficient enhancement of first hyperpolarizability is attributed to the better delocalization of the π-electron system and the more obvious degree of charge transfer. Therefore, these kinds of complexes might be promising candidates for designed as proton driven molecular second-order NLO switching.

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