Conductance switching in diarylethenes bridging carbon nanotubes

Abstract

The recently reported photoswitching of diarylethene derivative molecules bridging carbon nanotube (CNT) contacts is theoretically analyzed. The short lifetime of the lowest unoccupied molecular orbital (LUMO) indicates that neither the open nor closed form of the molecule can be photoexcited into a charge-neutral excited state for any appreciable length of time preventing photochromic ring opening. Analysis of the highest occupied molecular orbital (HOMO) and LUMO lifetimes also suggests that photoexcitation results in oxidation of the molecules. This either reduces the quantum yield of photochromic ring closing, or it gives rise to the possibility of oxidative ring closing. Analysis of the resistance values and energy levels indicates that the HOMO energy levels of the closed isomers relevant for transport must lie within a few k(B)T of the CNT Fermi level. For armchair contacts, the change in resistance with isomer or substituent group is the result of shifts in the energy level of the molecular HOMO. The coupling of the molecular HOMO to the CNT contacts is insensitive to the isomer type or substituent group. For zigzag CNTs, the conductance is dominated by surface states at the Fermi level on the cut ends of the CNTs so that the conductance is relatively insensitive to the isomer type, and the conductance switching ratio is low. Multiple bridging molecules can interact coherently, resulting in energy splitting, shifting, and interference that cause a nonlinear change in conductance with increasing numbers of molecules. Instead of a factor of 3 increase in conductance expected for three independent channels, a factor of 10(3) increase in conductance is obtained for three bridging molecules.

Conductance Switching and Mechanisms in Single‐Molecule Junctions

“…This is in excellent agreement with our original design (Figure 1), which implies that the on/off conductance ratios highly depend on the side groups outside the switching core for single-molecule junctions. [4] Thus, the conductance switching is dominated by the changes in the molecular energy levels as a result of either conformation transformation or the side group substitution. These optoelectronic switching phenomena are very reproducible since we observed the consistent photoswitching effect in many devices (at least 19 working devices for 1, 7 for 2, and 13 for 3).…”

“…Another remarkable feature of the diarylethene molecules used in this study is that only negligible changes in the molecular length ( 0.2 ) happen when they switch back-and-forth between open/closed states ( Figure S2 and Table S1). In conjunction with their superior thermal stability and fatigue resistance, these significant electronic and structural properties place diarylethene molecules as ideal candidates for building light-driven molecular switches as demonstrated theoretically [4] and experimentally. [5] However, a longstanding challenge is to conserve these promising properties in solution when the diarylethene molecules are sandwiched between solid-state molecularscale electrodes.…”

Electron transport through polyene junctions in between carbon nanotubes: An ab initio realization

“…Theoretical discussions have also been made on how the transmission is affected by the length of molecule, the size of CNTs [12], the geometry and coupling strength of the contact [13,14], the specific molecular species, and the chemical end groups of CNT leads' cut edge [15][16][17][18][19]. The interference effect also occurs in such a structure when multiple molecules are bridging the CNT leads.…”

“…Angle h is so defined to describe the relative positions of two contact sites, when two polyenes are in parallel and bridging the electrodes, providing that one of the polyenes uses site 1. TB (solid) and ab initio (dashed) results of the one polyene case, and the two polyene case of h ¼ p(1,17).…”

Theoretical investigation on remote-control photocycloreversion of dithienylethene driven by azobenzene chromophores

“…Photochromic dithienylethene (DTE) derivatives, which can undergo reversible photoisomerization by appropriate irradiation, have attracted more and more attention due to their wide applications in optical switches and memories, molecular machines, and nano-devices [1][2][3][4][5][6][7][8]. Usually the irradiation light on DTE must properly match the absorption band of its isomers, according to the Grotthuss-Draper law (also called the principle of photochemical activation), which states that only that light which is absorbed by a system can bring about a photochemical change [9].…”