α-Position Tricyano Engineering in Anthracene and Pyrene Push–Pull Chromophores for Tunable Electronic Materials

A series of push–pull π-conjugated chromophores based on anthracene and pyrene cores was designed to examine how progressive substitution of electron-withdrawing groups modulates optical, electrochemical, and charge-transport properties. Eight molecules were synthesized, including ester-, mixed ester/cyano-, dicyano-, and tricyano-substituted derivatives. The terminal tricyano compounds 2-(anthracene-9-yl)ethene-1,1,2-tricarbonitrile ( ATCN ) and 2-(pyrene-1-yl)ethene-1,1,2-tricarbonitrile ( PTCN ), serve as the strongest acceptor members of the series. Optical absorption depicted bathochromic shifts for ATCN and PTCN relative to their dicyano analogues, and enhanced intramolecular charge-transfer character. Cyclic voltammetry reveals reduced band gaps ∼1.27 eV for ATCN and ∼1.26 eV for PTCN, with higher electron affinity for nitrile-rich derivatives compared to ester-containing analogs. Thin-film measurements indicate space-charge-limited current transport. Contact-mode AFM revealed that ATCN forms three-dimensional crystalline islands (∼629 nm step height), while PTCN forms a comparatively continuous film (∼349 nm). These morphological differences correlate with electron mobility; ATCN exhibits values nearly 2 orders of magnitude higher than PTCN. This enhancement is attributed to the reduced torsional distortion of the anthracene framework. Furthermore, time-dependent density functional theory and natural transition orbital analyses support these trends, highlighting α-position tricyano substitution as an effective approach for tuning polyaromatic push–pull chromophores.