The optical properties (absorption/emission) of compounds 1-4 were investigated in diluted DCM solutions (c = 5.10 -6 mol.L -1 , Fig. and Table ). 1-4 display large UV-vis absorption bands in the visible range that were attributed by TD-DFT to -* transition (HOMO-LUMO) without significant contribution from the P-atom (Table ). Due to the rotation of the aryl group, in solution several conformers may coexist, which is supported by DFT calculations: except for 1, conformers having similar energies were found for 2-4, and these isomers have slightly different absorption wavelengths. As expected, the extension of the -skeleton leads to a bathochromic/hyperchromic shifts. All derivatives are also luminescent in diluted solution and show broad and unstructured emission in the blue region, with a large Stokes shift (Table and Fig. ). These emissions display a lifetime in the range of the ns (Table ). The molecular structures of 1-4, with their heterocycle-substituted stilbene backbones, makes them ideal synthons to promote photoinduced intramolecular cyclization. Indeed, the reaction of 1 and 2 in the "Katz" conditions (h, I2, propylene oxide) leads to the formation of phenanthrene-(5, Scheme 2) and picene-substituted phosphetene oxides (6, Scheme 2) in good yields (70-72%). In the case of 3-4, the reaction does not stop after the first cyclization, and a second cyclization occurs to yield planar PAH substituted phosphetene 7 and 8 (74%-83%). All the derivatives were fully characterized by multinuclear NMR, mass spectrometry and the structure of 5 and 6 were further confirmed by Xray diffraction (Scheme 2). Again, the structures consist in a racemic mixture of enantiomers and the geometry of the Pring is not significantly altered by the cyclization. In these systems, the polyaromatic scaffold is mostly planar (maximal deviation from the mean polyaromatic plane in 6: 0.14 Å). The NICS(0) patterns confirm that these PAHs nicely agree with Clar's criterion (Table -S9) despite the presence of the P-heterocycle. No intermolecular interactions based on -stacking of the PAH framework can be observed in the packing.