The efficiency of organic molecular emitters is limited by intersystem crossing (ISC) into low-lying non-emissive triplet states, which are favored over the emissive singlet states due to spin statistics The triplet states are furthermore favored energetically over singlets with the same electron configuration in accordance with Hund's rule, thereby making reverse ISC (RISC) less efficient (E(S 1 -T 1 ) > 0, Figure ). Recently, it was discovered that the gap between the lowest excited singlet (S 1 ) and triplet (T 1 ) states of a class of azaphenalenes is inverted (E(S 1 -T 1 ) < 0, Figure ). RISC is more efficient than ISC in cyclazine and heptazine because S 1 is thermodynamically favored over T 1 , as shown in Figure . Violations of Hund's rule can occur when the exchange interaction is minimized by reducing the overlap between the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO). As standard density functional theory-based methods struggle with Hund's rule violations, azaphenalenes were only recently identified as inverted gap emitters using coupled cluster methods. Fig. ) Simplifed Jablonski diagrams of conventional and inverted state ordering. b) Azaphenalenes and isopyrene with inverted singlet-triplet gaps. c) Related non-alternant molecules; bicalicene is an example of a higher-lying Hund's rule violation. Computed at the EOM-CCSD/augcc-pVDZ//ωB97X-D/def2-TZVP level.