Emergent Properties of an Organic Semiconductor Driven by its Molecular Chirality

Abstract

Chiral molecules exist as pairs of nonsuperimposable mirror images; a fundamental symmetry property vastly underexplored in organic electronic devices. Here, we show that organic field-effect transistors (OFETs) made from the helically chiral molecule 1-aza[6]helicene can display up to an 80-fold difference in hole mobility, together with differences in thin-film photophysics and morphology, solely depending on whether a single handedness or a 1:1 mixture of left- and right-handed molecules is employed under analogous fabrication conditions. As the molecular properties of either mirror image isomer are identical, these changes must be a result of the different bulk packing induced by chiral composition. Such underlying structures are investigated using crystal structure prediction, a computational methodology rarely applied to molecular materials, and linked to the difference in charge transport. These results illustrate that chirality may be used as a key tuning parameter in future device applications

Outstanding Chiroptical Features of Thin Films of Chiral Oligothiophenes

“…Chirality in organic optoelectronic devices is a topic that is rapidly gaining interest . There is at least a two‐fold interest: in the first place it can constitute a means to drive and control the supramolecular order of π‐conjugated molecules constituting the active layers of the devices, and secondly it opens the way to highly specialized applications, such as producing (CP‐OLED), or detecting (CP‐OFET) circularly polarized (CP) light or specifically responding to analyte enantiomers in analytical sensors . Moreover, molecular chirality is a unique way to manipulate electron spins and to construct spin filters .…”

Intense redox-driven chiroptical switching with a 580 mV hysteresis actuated through reversible dimerization of an azoniahelicene

“…[5][6][7] Of particular interest are helicene-based switches, 8 since the exceptionally intense chiroptical properties 9-11 of helicenes could lead to a large increase in the magnitude of the differential chiroptical signal and such molecules have already been successfully exploited in technological applications. [12][13][14][15][16][17] In most cases, the switching of these helicenes through changes in electrochemical potential (redox switching) has been achieved via reduction or oxidation of electronically biased helicenes [18][19][20][21] or helicene-coordinated transition metals, [22][23][24][25][26] leading to strong chiroptical switching D(De) of up to 135 M À1 cm À1 (see Fig. 1A left) 21 and even chiroptical switching at wavelengths suitable molecular systems are based on simple, reversible redox reactions with little or no significant structural change of the helicene, 27 the difference between the ''ON'' and the ''OFF'' potentials (redox hysteresis) is small and on the order of 60 mV (e.g.…”

“…We have previously found 1-aza [6]helicene [36][37][38] (1) to be a highly useful scaffold for chiroptical applications, especially in the context of organic electronic devices. 12,13,17 Based on the electrochemical behaviour of related non-chiral systems, 39,40 we anticipated that quarternisation of the nitrogen atom would afford a system (2 + ) that could provide a new intermolecular pathway to strong chiroptical switching 21,41,42 with a large redox hysteresis. As such, pyridinium helicene 2 + BF 4 À was synthesised by treating racemic or enantiopure aza [6]helicene 38 (1) with trimethyloxonium tetrafluoroborate (see ESI † for details).…”

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

“…Fuchter and co‐workers demonstrated a circularly polarised light‐detecting organic field‐effect transistor (OFET) based on enantiopure ( M )‐ or ( P )‐1‐aza[6]helicene as the active element of a semiconducting thin film . The same authors also described remarkable differences in hole mobility measured in OFETs constructed from either racemic or enantiopure 1‐aza[6]helicene in a thin film . Naaman and co‐workers demonstrated the chirality‐induced spin selectivity (CISS) effect in supramolecular assemblies of cationic ( M )‐ or ( P )‐[4]helicenes .…”

“…[4] The same authorsa lso describedr emarkable differences in hole mobility measured in OFETsc onstructed from either racemic or enantiopure 1-aza [6]helicene in athin film. [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.…”