Molecular rectification: asymmetric current–voltage curves from self-assembled monolayers of a donor–(π-bridge)–acceptor dye

Self-assembled monolayers: from simple model systems to biofunctionalized interfaces

“…For instance, Ashwell and coworkers used an STM tip to contact a molecule comprising donor and acceptor groups linked via an electron bridge (π system), i.e. 'D-π-A', and have found rectification behaviour [108], as have many others.…”

Induced rectification from self-assembled monolayers of sterically hindered π-bridged chromophores

“…However, recent studies have confirmed molecular rectification from LB films 8,9 of C 16 H 33 -Q3CNQ contacted by non-oxidisable electrodes as well as self-assembled Au-S-C n H 2n -Q3CNQ monolayers. 9,10 Metzger and co-workers 7b,11 have argued that the rectifying behaviour is induced, at least in part, by the insulating tail but this conflicts with experimental evidence: 9,10 e.g. a systematic lengthening of the alkyl tail provides no significant variation of the rectification ratio from Au-S-C n H 2n -Q3CNQ structures where 3 ¡ n ¡ 12; exposure to acid and then base causes the I-V characteristics of these analogues to reversibly alter between symmetrical and rectifying as the donor-acceptor combination is first disrupted and then restored.…”

“…It has been demonstrated by scanning tunnelling spectroscopy (STS) with the SAM contacted by coated gold probes: Au-S-C 10 H 20 -Q3CNQ//C 10 H 21 -S-Au. 10 LB and self-assembling derivatives of five different D-p-A chromophores [8][9][10][12][13][14][15] and a conjugated oligomer with electrondonating bithothene and electron-accepting bithiazole segments 16 are known to exhibit electrical asymmetry when contacted by non-oxidisable electrodes. The polarity for rectification is dependent upon the dipole orientation and, thus, molecules connected via their acceptors (Au-S-C n H 2n -A-p-D) and donors (Au-S-C n H 2n -D-p-A) exhibit higher currents in opposite quadrants of the I-V plot.…”

Molecular rectification: self-assembled monolayers of a donor–(π-bridge)–acceptor chromophore connected via a truncated Au–S–(CH2)3bridge

“…Scanning probe spectroscopy was used to monitor the electrical asymmetry with a gold tip coated with decanethiolate, the alkyl tail matching the link between the chromophore and substrate: Au-S-C 10 H 20 -Q3CNQ//C 10 H 21 -S-Au (ref. 13). By assembling the electrically nonlinear dye on the tip rather than the substrate, thereby altering orientation of the Q3CNQ unit, reverses the polarity for rectification.…”