AbstractThis article details the preparation, photophysical and electrochemical investigation of four novel polyaromatic square‐planar platinum(II) bis(acetylide) complexes, incorporating either a planar hexa‐peri‐hexabenzocoronene (L2) or its uncyclised ethynyl‐hexaphenylbenzene precursor (L1). Complexes in both cis and trans geometries (cis‐[Pt(L)2(dppe)] [C1, C2; dppe = 1,2‐bis(diphenylphosphanyl)ethane] and trans‐[Pt(L)2(PPh3)2] (T1, T2) were successfully prepared and fully characterised. The low‐energy bands of the UV/Vis absorption spectra for the uncyclised family (L1, C1, T1) and for the cyclised family (L2, C2, T2) exhibit a redshift in the order trans > cis > ligand, indicating enhanced π‐conjugation along the molecular axis in trans configuration. Each PtII complex is dual luminescent and possesses a high‐energy ligand‐centred fluorescence and a lower energy emission with significant phosphorescent character facilitated by the high spin‐orbit coupling of the heavy platinum metal centre. Notably, cis‐ and trans‐L2 complexes exhibit remarkably long lifetimes in degassed CH2Cl2 at room temperature (trans: 30.9 μs; cis: 18.3 μs) for sharp phosphorescence at λ = 578 nm.