Odd-even effect of the switching performance for dimethyldihydropyrene/cyclophanediene single-molecule switch modulated by carbon atomic chains

Improving the switching performance of single-molecule switches is one of the major pursuits in the research of molecular switches. Here, by applying the first principles method based nonequilibrium Green's function formulisms, a single-molecule switch comprised of a dimethyldihydropyrene(DHP)/cyclophanediene(CPD) photosensitive molecule connected to gold electrodes by carbon atomic chains (CACs) has been designed. To optimize the switching performance of the DHP/CPD single-molecule switch, the length of CACs has been varied, where the number n of carbon atoms in the CACs has been sequentially changed from 1 to 6. The numerical results suggest that there is an evident odd-even effect in the switching performance of the DHP/CPD single-molecule switch modulated by the odevity of n (nodd or neven). The ON/OFF ratio is enhanced by one order of magnitude when CACs with neven carbon atoms are adopted in comparison with the cases of CACs with nodd carbon atoms. Further analysis reveals that the atomic bondings are distinctly different for the CACs with nodd and neven carbon atoms, which results in large difference in alignments of molecular states with EF of electrodes. Meanwhile, the conducting channels around EF for CPD are dramatically changed with respect to the odevity of n, which leads to a large modulation of the switching performance of the DHP/CPD single-molecule switch. Our results suggest a promising and efficient way to optimize the switching performance of single-molecule switches.