Halogenation of a Nonplanar Molecular Semiconductor to Tune Energy Levels and Bandgaps for Electron Transport

Abstract

Though peripheral halogen substitution is a known strategy to lower the lowest unoccupied (LUMO) and highest occupied (HOMO) molecular orbital energy levels of planar molecular semiconductors, this strategy has not been explored in conformationally contorted systems. We demonstrate that substitution of peripheral hydrogens with fluorine and chlorine can effectively lower the energy levels of contorted hexabenzocoronene (cHBC) despite its nonplanar conformation. The HOMO energy level lowers comparably with fluorine and chlorine substitution. Due to chlorine’s ability to accommodate more electron density than fluorine, chlorination lowers the LUMO energy level more effectively compared to fluorination (31–60 meV/F versus 53–83 meV/Cl), resulting in a narrowing of the optical bandgap. We find the preference for electron transport to increase with increasing halogenation of cHBC. As an example, thin-film transistors fabricated with 8F-8Cl-cHBC demonstrated electron mobilities as high as 10–2 cm2/(V s) and solar cells with 8F-8Cl-cHBC and poly­(3-hexylthiophene), P3HT, showed power-conversion efficiencies as high as 1.2%.

Design of Hexabenzocoronene Derivatives as Non-Fullerene Acceptors in Organic Photovoltaics by Bridging Dimers and Modulating Structural Twists

“…The computational and the experimental data were listed in Table S2 and plotted in Figure S2. The results showed that the maximum absorption wavelength of PBE0 was 433 nm, which is in good accordance with the experimental value 400 nm . Therefore, the absorption spectra of 1–14 were simulated by TD‐PCM‐PBE0/6‐31G(d) method.…”

“…The results are shown in Table S1. Meantime, B3LYP has been proven feasible to predict the geometries and the electronic structures of HBC derivatives . The absorption spectra and excited‐state energies were obtained with TD‐DFT calculations based on the optimized ground‐state geometries .…”

“…Compared with bridging dimerization studies, there is still no systematic and unambiguous understanding regarding the solution of introducing/utilizing structural twists. Recently, Loo et al designed an aromatic molecule contorted hexabenzocoronene halogenated derivative (8F‐8Cl‐cHBC), whereas the PCE of this device is 1.2% with poly(3‐hexylthiophene) as the donor . The structural characteristics of HBC have 12 bay positions to discuss 1–6 kinds of connections; this will allow us to systematically explore the degree of twists in the performance of the acceptor material.…”

Chlorination of phenylallene derivatives with 1-chloro-1,2-benziodoxol-3-one: synthesis of vicinal-dichlorides and chlorodienes

“…Organochlorine compounds are vital as polymer precursors [1], as pharmaceuticals [2–3] and agrochemicals [4–6] and as functional materials [7–8]. And as there is an abundance of chlorine-containing natural products, the synthesis of chlorinated functional groups, such as allyl- and vinyl chlorides, can represent challenging obstacles that practitioners of natural product synthesis must surmount [9–12].…”

Controlled Growth of Ultrathin Film of Organic Semiconductors by Balancing the Competitive Processes in Dip-Coating for Organic Transistors

“…[1][2][3][4][5][6][7][8][9] Generally, the thickness of organic semiconductor layer in organic electronic devices is in the range of several tens of to hundreds of nanometer (nm), which consists of tens of or more molecular layers. [10][11][12][13][14][15][16] On the other hand, ultrathin film (< 15 nm, Figure 1a) of organic semiconductors represents a kind of nano-scale film consisting of monolayer to few molecular layers (Figure 1b).…”