Herein, we demonstrate an efficient synthesis of two antiaromatic constitutional isomers of pyrene-fused dicyclopenta[a,f]naphthalenes (PCPNs) 1a and 1b featuring 44 π-conjugated electrons. Notably, the thermodynamic stability of PCPNs can be tuned by ortho-fusing pyrene moieties to either the a or b bond of dicyclopentanaphthalene (CPN) leading to labile 1,5- (1a) or stable 2,6-naphthoquinodimethane (NQDM) (1b) configurations, respectively. Both isomers 1a and 1b exhibit moderate open-shell biradical characters (y0) of 0.48 and 0.44 and narrow energy gaps of 1.0 and 1.1 eV, respectively. Moreover, the spectroscopic and spin properties of radical cation and anion species of 1a and 1b are elucidated by in situ EPR/UV-vis-NIR spectroelectrochemical investigations. Furthermore, a solution-processed field-effect transistor of 1b was fabricated, manifesting its promising potential in organic electronics.