Oligoacenes:  Theoretical Prediction of Open-Shell Singlet Diradical Ground States  [J. Am. Chem. Soc. 2004, 126, 7416−7417].

The Most Stable and Fully Characterized Functionalized Heptacene

“…This solution had been degassed by bubbling argon, which had been passed through activated oxygen-scavenger RIDOX and CaSO 4 , for 30 min with protection from light. The reaction was allowed to proceed in the dark and to reach room temperature overnight, it was then quenched by pouring into 20 mL of saturated NH 4 Cl, the aqueous layer was then extracted with ethyl acetate (3 10 mL). The combined organic layers were washed with water (2 15 mL), brine (1 15 mL) and then dried over MgSO 4 .…”

“…The reaction was allowed to proceed in the dark and to reach room temperature overnight, it was then quenched by pouring into 20 mL of saturated NH 4 Cl, the aqueous layer was then extracted with ethyl acetate (3 10 mL). The combined organic layers were washed with water (2 15 mL), brine (1 15 mL) and then dried over MgSO 4 . Upon evaporation of all solvents under reduced pressure on a rotary evaporator, the crude product was chromatographed on a SiO 2 column with an eluent gradient starting with hexanes, followed by 1-5 % ethyl acetate in hexanes.…”

“…[4,5] Hence, the electronic properties of the longer acenes have long been a subject of debate. [6] While the physical properties of the smaller linear PAHs (2 with n 5) are well explored, our knowledge of longer acenes is limited for two major reasons: 1) the synthetic challenge in their production and their insolubility and 2) their extreme instability with increased length, which makes them characterizable only by electronic spectroscopy in a matrix at low temperatures.…”

The radical character of the acenes: A density matrix renormalization group study

“…1,2 Due to their technological potential [3][4][5] and their intrinsic value as models for more complex conjugated molecules, they have been the subject of many theoretical and experimental investigations. [6][7][8][9][10][11][12][13][14] In a number of recent studies, it has been proposed that longer acenes may possess an unusual electronic ground state that is not the simple closed-shell singlet suggested by molecular orbital arguments. Based on extrapolating the experimental singlet-triplet gap of the acenes up to pentacene, Angliker et al 7 predicted that the ground state of higher acenes from nonacene upwards would be a triplet.…”

Spin transport in highern-acene molecules

“…The lowest unoccupied molecular orbitals (LUMOs) are the corresponding empty spin-split orbitals, so that the HOMO-LUMO gap is an exchange split gap. Recent calculations predicted a spin singlet ground state for the higher acenes [7,8,11,12,18] as a result of the antiferromagnetic coupling between the two orbitally degenerate HOMOs. This contrasts earlier predictions of a ferromagnetic (triplet) ground state [10,19,20].…”