By the combined retrosynthetic and computational analysis we selected a group of potentially interesting and synthetically accessible laterally π-expanded fused indoloindolizines for further exploration of their optoelectronic properties. Our synthetic protocol (vide infra) allows benzannulation on positions 2,3 (on the indole part of the molecule), 5,6, and 7,8 on the indolizine moiety. Therefore, further theoretical analysis is focused on derivatives that were synthetically attainable. To examine our hypothesis, we computed HOMO-LUMO gaps and assessed the aromaticity of all rings utilizing magnetically induced current density (MICD), nucleus-independent chemical shifts (NICS), and isomerization stabilization energy (ISE) , at DFT (B3LYP /def2-TZVPP ) computational level. As a rule of thumb, chemists expect that the band gap in conjugated molecules shrinks as the size of the conjugated π-system increases. This trend is well-established for linear polycyclic aromatic hydrocarbons (PAHs). A recent comprehensive big-data study by Gershoni-Poranne and co-workers further validated this phenomenon, demonstrating a clear correlation between the expansion of the π-system and the reduction of the band gap in PACs. However, the intrinsic difference between the aromaticity, as well as the HOMO-LUMO gap of indole and indolizine makes the trends in the variation of the band gap complicated in the case of indoloindolizine derivatives. Nevertheless, listing the studied molecules according to their HOMO-LUMO gap reveals a structure-dependent periodic pattern of HOMO-LUMO gap variation (Figure ). To construct a periodic table for indoloindolizines we followed four simple rules. (1) From the top left to the bottom right the band gap of molecules decreases. The only exceptions to this rule are M3 and M4 where DFT predicts the band gap of M4 to be 0.01 eV higher than M3 but for the sake of the fourth rule, we place M3 before M4 in the table. (2) We keep all molecules that have equal or fewer rings than the first molecule in a row of the periodic table on the same row. Inspecting the variation of the HOMO-LUMO gaps with respect to structure and aromaticity reveals an interesting trend. Within each row of our periodic table, we observe that as the HOMO-LUMO gap decreases, the isomerization stabilization energy (ISE) of the indolizine moiety increases. Notably, in each row, the ISE of the 6-membered ring of the indole moiety remains almost constant. From top to bottom of each group, where the number of attached benzene rings on the 6-membered ring of indolizine moiety is conserved, the addition of more benzene rings to the other side of the molecule has two effects. First, the aromaticity of the indolizine moiety decreases as it is reflected in the decrease of the ISE of the indolizine fragment. Interestingly, the ISE of the 6-membered ring of indole also decreases more rapidly than the 6-membered ring of the indolizine moiety. These two simultaneous changes point to the loss of the aromatic stabilization energy in the indole unit in each group from top to bottom. Therefore, in each group, the HOMO-LUMO gaps decrease from top to bottom. Akin to the periodic table of elements, one may fill the gaps in the periodic table presented in Figure . A more comprehensive version of this periodic table with substituted indolizines is presented in Figure . Inspecting the current density passing through the 5-membered ring of these systems reveals a similar trend but with less sensitivity to the HOMO-LUMO gap variation trend. The current density values for all studied systems are collected in Figure for comparison with the ISEs. Our initial analysis suggests that double benzannulation of positions 5,6 and 7,8 on the indolizine moiety is the most efficient method to increase the band gap as M2 has the largest band gap in its row. Mono-benzannulation in position 7,8 gives a slightly higher HOMO-LUMO gap than in the corresponding isomers with a benzene ring added in the 5,6 position of indoloindolizine moiety. Finally, benzannulation of the indole moiety increases the ISE of the indolizine part which results in lowering the band gap, as seen on the right side of our indoloindolizine periodic table (Figure ).