We performed IRC calculations and geometry optimizations to obtain the reactive conformers for the lowest energy transition states of azofurans 1-TS and 2-TS, and azothiophenes 3-TS and 4-TS. Figure shows the optimized reactants 1-Z and 2-Z, along with their optimized transition structures 1-TS and 2-TS, and Figure shows the energies and geometries of transition structures of (3-4)-Z, (3-4)-TS. 2-Z has an isomerization barrier that is 8.5 kcal mol -1 higher than the corresponding azofuran 1-Z. We sought to understand how the electronic structures of (1-4)-Z affect the 10 6 -fold range in half-lives. The transition states feature coplanar aryl groups; we quantify this coplanarity with an out-of-plane angle (θ). θ is the angle between two normal vectors to the planes of the aryl rings. We performed time-dependent density functional theory (TD-DFT) calculations to predict the nature of the electronic transitions and vertical excitation energies of the E-isomers. The corresponding λ max derived from the vertical excitation energies of 1-E, 2-E, 3-E, and 4-E are 382, 304, 400, and 317 nm, respectively. The experimental λ max of (3,3) azothiophene is 332 nm. 1-E, and 3-E have λ max which are redshifted by 78 nm and 83 nm relative to 2-E and 4-E, respectively. To understand the origin of the 96 nm range in λ max along this series, we computed the frontier molecular orbitals (FMOs) for 1-E, 2-E, 3-E, and 4-E (Figure ). 1-E and 3-E have fully delocalized π-systems across the diazo bond, while 2-E and 4-E show interrupted π-electron density due to their cross-conjugated nature. Cross-conjugated molecules have incomplete π-delocalization, which has been shown to impact photophysical properties by increasing molecular band gaps and lowering λ max absorption. Cross-conjugation has also been found to affect the reversibility and activation free energy barriers of Diels-Alder and thiol addition reactions. The delocalization effect in 1-E and 3-E leads to higher-lying HOMOs and lower-lying LUMOs relative to 2-E and 4-E, leading to increased HOMO-LUMO gaps. The HOMO for 1-E is -6.18 eV, 0.41 eV higher than the HOMO for 2-E (-6.59 eV), and the HOMO for 3-E is -6.32 eV, 0.25 eV higher than the HOMO for 4-E (-6.58 eV). The LUMO for 1-E is -2.64 eV, which is 0.47 eV lower than the LUMO for 2-E (-2.17 eV), and the LUMO for 3-E is -2.81 eV, 0.53 eV lower than the LUMO for 4-E (-2.27 eV). The HOMO-LUMO gaps of 1-E and 2-E are 3.54 eV and 4.42 eV (a 0.88 eV difference), and the same gaps are 3.51 eV and 4.31 eV for 3-E and 4-E, a difference of 0.80 eV.