Asymmetric Diradical Made y -Core Modification: Comparisons with Its Symmetric Parents

Abstract

Asymmetric conjugated diradicals are much less common than their symmetric counterparts because they expand th e feasibility of symmetry, but they also present some detrimental aspects. Hence, studies comparing analogue symmetric and asymmetric diradicals are of interest. Previous studies regarding the structure of asymmetric conjugated diradicals only focused on analyzing different radical moieties attached to the same $$-core bridge, while none of them explored the diradicals with asymmetric $$-core (same radical moieties). Herein, we report a series of azine derivatives PNP-n (n = 1–3). The symmetric diradicals PNP-1 and PNP-3 have a $$-core comprising two benzenes or two thiophene units linked to a central azine, respectively. Replacing a benzene unit with thiophene in symmetric PNP-1 diradical yields the asymmetric PNP-2 diradical altering the energy gap and the spin-spin coupling strengths thus modulating the diradical characteristic. This work highlights the advantages and drawbacks of transitioning from symmetric to asymmetric diradicals, while also providing a molecular-level description of their intrinsic properties, despite their similar chemical compositions