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In this paper we investigate the role of electron correlation in predictingthe S$_1$-S$_0$ and T$_1$-S$_0$ excitation energies and hence, thesinglet-triplet gap ($\Delta$E$_{ST}$) in a set of cyclazines which act astemplates for potential candidates for 5th generation Organic Light EmittingDiode (OLED) materials. This issue has recently garnered much interest with thefocus being on the inversion of the $\Delta$E$_{ST}$, although experiments haveindicated near degenerate levels with both positive and negative being withinthe experimental error bar (\emph{J. Am. Chem. Soc. 1980, 102: 6068 , J. Am.Chem. Soc. 1986, 108: 17} ). We have carried out a systematic and exhaustivestudy of various excited state electronic structure methodologies andidentified the strengths and shortcomings of the various approaches andapproximations in view of this challenging case. We have found that neardegeneracy can be achieved either with a proper balance of static and dynamiccorrelation in multireference theories or with state-specific orbitalcorrections including its coupling with correlation. The role of spincontamination is also discussed. Eventually, this paper seeks to producebenchmark numbers for establishing cheaper theories which can then be used forscreening derivatives of these templates with desirable optical and structuralproperties. Additionally we would like to point out that the use ofDLPNO-STEOM-CCSD as the benchmark for $\Delta$E$_{ST}$ (as used in \emph{J.Phys. Chem. A 2022, 126: 8: 1378, Chem. Phys. Lett. 2021, 779: 138827}) is nota suitable benchmark for this class of molecules.

Benchmark Computations of Nearly Degenerate Singlet and Triplet states of N-heterocyclic Chromophores : I. Wavefunction-based Methods