Biomedical subjects
Publications and source records attributed to Barbara Urasinska.
A self-assembled arylene-ethynylene molecular wire with a rigid 7 nm long backbone exhibits symmetrical current-voltage (I-V) characteristics and a single-molecule current of 0.35 +/- 0.05 nA at 0.3 V; these data are supported by theoretical calculations.
Self-assembled monolayers of cationic donor-(pi-bridge)-acceptor dyes coupled with anionic donors exhibit asymmetric current-voltage (I-V) characteristics when contacted by Au or PtIr probes. Rectification ratios of 3000 at +/- 1 V are obtained from Au-S-C10H20-A+-pi-D|D-|Au structures in which the cationic moiety is 5-(4-dimethylaminobenzylidene)-5,6,7,8-tetrahydro-isoquinolinium and the counterion is copper phthalocyanine-3,4',4'',4'''-tetrasulfonate (SAM ). Similar behaviour, with a high rectification ratio of 700-900 at +/- 1 V, is also obtained for the CuPc(SO3-)4 salt of 4-[2-(4-dimethylaminonaphthalen-1-yl)-vinyl]-quinolinium (SAM ). The properties are dependent upon the D-pi-A+ moieties which, for these highly rectifying salts, have sterically locked non-planar structures causing the conjugation to be effectively broken. Its effect on the electrical asymmetry is less spectacular when the cationic species is sterically unhindered: the rectification ratio decreases to 15-70 at +/- 1 V for films of the 4-[2-(4-dimethylaminophenyl)-vinyl]-pyridinium salt (SAM ), which has single-ring substituents on opposite sides of the -CH=CH- bridge and an almost planar D-pi-A+ structure. Rectification ratios from the sterically hindered structures are on a par with electrical asymmetries from metal-insulator-metal (MIM) devices where oxide-induced Schottky barriers dominate the behaviour.
Self-assembled monolayers (SAMs) of arylene-ethynylene oligomers that incorporate electron-accepting 9-fluorenone and 9-[(4-pyridyl)methylene]fluorene units in the backbone exhibit symmetrical current-voltage (I-V) characteristics, but rectifying junctions with current ratios of 20-80 at +/-1 V have been obtained by protonating these wire-like molecules and ionically coupling with anionic donors.