Table 1. Highest-level available literature estimates from computational studies for vertical and adiabatic singlet–triplet energy gaps (kcal mol^–1) in oligoacenes.

Molecule	Vertical gap a	Adiabatic gap	Average adiabatic gap
Naphthalene	76.0	65.8 a ,63.5 b ,61.0 c ,67.3 d	64.4 f
Anthracene	56.8	48.2 a ,44.8 b ,44.0 c ,48.0 d ,46.1 e	46.2 f
Tetracene	40.4	33.5 a ,31.9 b ,31.9 c ,38.3 d ,34.8 e	34.1 f
Pentacene	31.3	25.3 a ,23.3 b ,23.4 c ,25.1 d	24.3 f
Hexacene	22.8	17.7 a ,17.6 b ,17.5 c ,21.9 d	18.7 f
Heptacene	18.1	13.4 a ,13.9 b ,14.5 d	13.9 f
Octacene	13.4	9.2 a ,11.5 b ,13.8 d	11.5 f
Nonacene	10.7	10.1 b ,10.6 d	10.4 f
Decacene	8.1	9.0 b	9.0
Undecacene	7.1	9.4 b	9.4
Dodecacene	NA g	8.9 b	8.9
Infinite chain h			5.1

^aCCSD(T)/CBS from ref. 21, where “CBS” denotes extrapolation to a complete one-electron basis set.

^bvRDM/CBS from ref. 19.

^cDMRG/DZ from ref. 17.

^dπ-MR-CISD + Q/CAS(8,8)/6-31G from ref. 85.

^eMRMP/cc-pVDZ from ref. 84.

^fAverage of the values in adiabatic gap column.

^gNot available.

^hFrom ref. 26.