Biradicaloid intermediates in photochemistry: spectroscopic and kinetic study of 1,4-perinaphthadiyl and related 1,8-naphthoquinodimethans

Calculations on 1,8‐naphthoquinone predict that the ground state of this diradical is a singlet

“…However, as would be expected for a hydrocarbon diradical with non‐disjoint MOs and as has been found experimentally, the ground state of 1,8‐ PND is computed to be a triplet. Consistent with the results of experiments, the predicted size of Δ E ST = 4.2 kcal/mol in 1,8‐ PND is large enough that the 1 A 1 state should not be populated at low temperatures.…”

“…One of the first conjugated, organic, diradicals to be investigated experimentally was 1,8‐perinaphthyldiyl (1,8‐ PND in Fig. ) . It can be viewed as a derivative of 1,8‐naphthoquinodimethane (1,8‐ NQDM ), whose π system is slightly perturbed by hyperconjugation with the CH 2 group that bridges the radical centers in 1,8‐ PND .…”

Generation and identification of 1,4-perinaphthadiyl radical cation—first observation of the electronic absorption spectrum of an ionized diradical

“…Neutral CND has a triplet ground state, 7 which implies that the two singly occupied MOs are very close in energy. If such a species is ionized, two states of different symmetry but similar energy can be formed, depending on which of the two nearly degenerate MOs is vacated.…”

“…[3][4][5] The ethylene bridged derivative, 7,8,9,10-tetrahydrocyclohepta[de]naphthalene-7,10-diyl (CND), which can be conveniently generated from the azo compound, 1,4-dihydro-1,4-ethanonaphtho [1,8-de] [1,2]diazepine (END), has received special attention as an intermediate in the intramolecular cycloaddition of 1,8divinylnaphthalene (DVN) to form cyclobut[a]acenaphthylene (CAN). [6][7][8] Spectroscopic characterization of reactive intermediates opens the way to kinetic studies of their reactivity and the determination of their thermochemical properties. Timeresolved studies of diradicals have provided lifetimes and reactivities of numerous diradical intermediates in solution, 9 including parent 1,8-naphthoquinodimethane.…”

Communication: Manipulating the singlet-triplet equilibrium in organic biradical materials

“…[1][2][3] Open-shell molecules created in this way display unique electronic structure and magnetic exchange interactions that allow investigation of the interplay between charge, structure, and magnetism. [4][5][6][7][8][9] When a ground or thermally accessible, paramagnetic state is generated, they also provide close insight into the behavior that is very promising for light harvesting, controllable reactivity, and spin valve applications. [10][11][12] 1,4-Diazidobenzene attracted our attention in this regard.…”