Photoinduced work function changes by isomerization of a densely packed azobenzene-based SAM on Au: a joint experimental and theoretical study

Abstract

Responsive monolayers are key building blocks for future applications in organic and molecular electronics in particular because they hold potential for tuning the physico-chemical properties of interfaces, including their energetics. Here we study a photochromic SAM based on a conjugated azobenzene derivative and its influence on the gold work function (Φ(Au)) when chemisorbed on its surface. In particular we show that the Φ(Au) can be modulated with external stimuli by controlling the azobenzene trans/cis isomerization process. This phenomenon is characterized experimentally by four different techniques, kelvin probe, kelvin probe force microscopy, electroabsorption spectroscopy and ultraviolet photoelectron spectroscopy. The use of different techniques implies exposing the SAM to different measurement conditions and different preparation methods, which, remarkably, do not alter the observed work function change (Φ(trans)-Φ(cis)). Theoretical calculations provided a complementary insight crucial to attain a deeper knowledge on the origin of the work function photo-modulation.

Atomistic simulations of charge transport in photoswitchable organic-graphene hybrids

“…Starting from the equilibrated all trans samples at 2.4 and 2.8 molecules nm −2 coverage topped with graphene, the photoswitching of the SAMs was performed (see the method section) until convergence at a final isomerization yield of 86% and 82%, respectively (figure S7). Variations in the thickness of azobenzene SAMs of about 4-7 Å when going from trans to cis isomer have been reported by experimental and theoretical studies [58,59], however in our case we do not observe such a marked difference, with a diminution of only about 1 Å (which increases to 2 Å in absence of graphene). This discordance can be attributed to the rather flexible molecular structure of the specific azobenzene derivatives investigated here (Scheme 1), that allows for local conformational deformations, as well as to the relatively disordered packing of the SAMs.…”

Effect of the Molecular Polarizability of SAMs on the Work Function Modification of Gold: Closed‐ versus Open‐Shell Donor–Acceptor SAMs

“…Recently, the concept of incorporating photoswitchable molecules in SAMs has been introduced to generate bistable systems providing a dynamic control over the work function shift and hence on the charge injection barriers . Prototypical molecules are azobenzene derivatives that can be switched reversibly between the trans and cis states under illumination.…”

Tuning the optical emission of MoS2 nanosheets using proximal photoswitchable azobenzene molecules

“…13 In this regard, optical tuning of devices represents a technological goal that can be achieved using photochromic compounds providing a straightforward way to realize photoswitchable devices. [14][15][16] For instance, chemisorbed, highly ordered azobenzene self-assembled monolayers (SAMs) are widely known to photoisomerize between trans and cis conformations. 17,18 Among various tunable properties of SAMs, which serve as the basis for sensors, 19 memory devices, 17,20 and organic thin-film transistors, 21 the quantum efficiency of a semiconductor in intimate contact can also be tuned.…”