Tetracyanoanthracenediacenaphthalimides as n-Type Organic Semiconductors: Control of Molecular Orientation

We investigated tetracyanoanthracenediacenaphthalimides (TCDADIs) as n-type organic semiconductors (OSCs) and assessed their molecular self-assembly in forming monolayers and thin films using optical absorption spectroscopy, scanning tunneling microscopy (STM), atomic force microscopy (AFM), and grazing incidence wide-angle X-ray scattering (GIWAXS). The absorption spectra, along with quantitative GIWAXS analysis, reveal the influence of molecular structure (alkyl chain length) and film processing conditions (annealing temperature and spin-coating speed) on the orientation of TCDADI molecules in films. Our findings indicate that increasing the spin-coating speed and annealing temperatures causes a transition from a mixed phase to a predominantly edge-on molecular orientation. This transition significantly enhances the electron mobility, from 0.01 to 0.05 cm² V^–1 s^–1 for TCDADI-C16 and from 0.13 to 0.20 cm² V^–1 s^–1 for TCDADI-C24. In addition, we highlight the potential of TCDADIs for photodetector applications, showing a photoresponse gain of over 2000 under white light.