All about (N-hexadecylquinolin-4-ium-1-yl)methylidenetricyanoquinodimethanide, a unimolecular rectifier of electrical current

We found unimolecular rectification in a single molecule, (N-hexadecylquino lin-4-ium-1-yl)methylidenetricyanoquinomethanide, in which the ground state is zwitterionic: D+-pi-A(-), and has a large dipole moment (43 D) while th e first excited state is undissociated: D-0-pi-A(0) (and has a smaller mome nt, between 3 and 9 D). The intervalence optical absorption band connecting these two states is strongly hypsochromic. Spectroscopic measurements (FTI R, NMR, VIS-UV, XPS) all confirm this assignment. This significant 'first s tep' to unimolecular electronics, i.e. a rectifier only 2.3 nm thick, confi rms a 1974 proposal by Aviram and Ratner. However, the 'real proof' that th e large current under forward bias actually travels through the molecule, h as not yet been obtained.