Chirality-Dependent Electron Spin Filtering by Molecular Monolayers of Helicenes

Abstract

The interaction of low-energy photoelectrons with well-ordered monolayers of enantiopure helical heptahelicene molecules adsorbed on metal surfaces leads to a preferential transmission of one longitudinally polarized spin component, which is strongly coupled to the helical sense of the molecules. Heptahelicene, composed of only carbon and hydrogen atoms, exhibits only a single helical turn but shows excess in longitudinal spin polarization of about P = 6 to 8% after transmission of initially balanced left- and right-handed spin polarized electrons. Insight into the electronic structure, that is, the projected density of states, and the spin-dependent electron scattering in the helicene molecule is gained by using spin-resolved density functional theory calculations and a model Hamiltonian approach, respectively. Our results support the semiclassical picture of electronic transport along a helical pathway under the influence of spin-orbit coupling induced by the electrostatic molecular potential.

Thermal Decoherence and Disorder Effects on Chiral-Induced Spin Selectivity

“…Chiral-induced spin selectivity (CISS) is an intriguing physical effect, first experimentally demonstrated in 1999, that manifests itself as spin-dependent transport in helical albeit nonmagnetic molecules. [1][2][3] Despite the large amount of experimental [4][5][6][7][8][9][10][11][12][13][14][15][16] and theoretical [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] work published so far, the ultimate origin of the CISS effect is still subject to debate. There seems to be, however, agreement that a combination of the helical conformation of the molecule, together with field and exchange effects, leads to an enhanced spin-orbit interaction that ultimately is responsible for the spin-dependent transmission of electrons in media without time reversal symmetry.…”

Chirality‐Controlled Self‐Assembly of Amphiphilic Dibenzo[6]helicenes into Langmuir–Blodgett Thin Films

“…[5] Naamanand co-workersdemonstrated the chirality-induced spin selectivity (CISS)e ffect in supramolecular assemblies of cationic (M)-or (P)- [4]helicenes. [6] Similarly,E rnst and co-workersd escribed chirality-dependent electron spin filtering by monolayerso fe nantiopure (M)-and (P)- [7]helicenes. [7] The monolayers/thin films of racemic/enantiopure helicenes are usually preparedb ys pin coating, drop casting,u ltra-high vacuum (UHV) deposition or throught he formation of self-assembled monolayers (SAM) on the surface of solidso rat the air-water interface.…”

“…[6] Similarly,E rnst and co-workersd escribed chirality-dependent electron spin filtering by monolayerso fe nantiopure (M)-and (P)- [7]helicenes. [7] The monolayers/thin films of racemic/enantiopure helicenes are usually preparedb ys pin coating, drop casting,u ltra-high vacuum (UHV) deposition or throught he formation of self-assembled monolayers (SAM) on the surface of solidso rat the air-water interface. Surprisingly,t he relativelys imple Langmuir-Blodgett (LB) technique has so far not been systematically explored in the contexto fh elicene chemistry,e ven though such assemblies can exhibit unique chiroptical and NLO properties as reported by Katz et al [3,8] (see above)a nd Siltanen et al [9] In these studies,helicene units are equipped with multiple long alkyl chains to support the Langmuir monolayer formation.…”

“…Naaman and co‐workers demonstrated the chirality‐induced spin selectivity (CISS) effect in supramolecular assemblies of cationic ( M )‐ or ( P )‐[4]helicenes . Similarly, Ernst and co‐workers described chirality‐dependent electron spin filtering by monolayers of enantiopure ( M )‐ and ( P )‐[7]helicenes …”

Double layer crystallization of heptahelicene on noble metal surfaces

“…The on‐surface crystallization of helical aromatic hydrocarbons, so‐called helicenes, serves as such a model system 9 . Beyond chiral recognition, however, helicenes on surfaces may also show interesting new phenomena, such as electron spin selectivity, electromechanics, or selective chiroptical response 10–13 …”