Effect of Ring Strain on the Charge Transport of a Robust Norbornadiene-Quadricyclane-Based Molecular Photoswitch.

Behabitu E Tebikachew,Gemma C Solomon,Alessandro Pirrotta,Karl Börjesson,Haipeng B Li,Kasper Moth-Poulsen,Joshua Hihath

doi:10.1021/acs.jpcc.7b00319

Abstract

Integrating functional molecules into single-molecule devices is a key step toward the realization of future computing machines based on the smallest possible components. In this context, photoswitching molecules that can make a transition between high and low conductivity in response to light are attractive candidates. Here we present the synthesis and conductance properties of a new type of robust molecular photothermal switch based on the norbornadiene (NB)–quadricyclane (QC) system. The transport through the molecule in the ON state is dominated by a pathway through the π-conjugated system, which is no longer available when the system is switched to the OFF state. Interestingly, in the OFF state we find that the same pathway contributes only 12% to the transport properties. We attribute this observation to the strained tetrahedral geometry of the QC. These results challenge the prevailing assumption that current will simply flow through the shortest through-bond path in a molecule.

Highlights

Integrating functional molecules into single-molecule devices is a key step toward the realization of future computing machines based on the smallest possible component, single molecules.[1−4]
UV−vis absorption spectroscopy of NB-1 was carried out in toluene, and the onset of absorption wavelength was found to be around 460 nm (SI: Figure S4(a)), which is significantly red-shifted from unsubstituted norbornadiene
This is attributed to the extended π-conjugation in NB-1, which enabled the photoisomerization with visible light

Summary

■ INTRODUCTION

Integrating functional molecules into single-molecule devices is a key step toward the realization of future computing machines based on the smallest possible component, single molecules.[1−4] In this context, molecular switches that can make a transition between high and low conductivity in response to external stimuli have attracted significant attention since they can add a unique electronic function to molecular-scale devices and at the same time provide insight into the charge transport mechanism at the nanoscale.[5−10]. It is one of the few examples of a T-type negative photochrome along with dimethyldihydropyrene.[18] The photoswitching properties of norbornadiene have been demonstrated and utilized to study intramolecular energy transfer in solution. This work brings more insight into the effect of quantum interference on charge transport in strained ring structures and suggests new candidates and perspectives on engineering molecular-level photoswitches

■ RESULTS AND DISCUSSION

■ CONCLUSION

■ ACKNOWLEDGMENTS

■ REFERENCES