On the generation of electronic ring currents under vibronic coupling effects

Abstract

We study the generation of electronic ring currents in the presence of nonadiabatic coupling using circularly polarized light. For this, we introduce a solvable model consisting of an electron and a nucleus rotating around a common center and subject to their mutual Coulomb interaction. The simplicity of the model brings to the forefront the non-trivial properties of electronic ring currents in the presence of coupling to the nuclear coordinates and enables the characterization of various limiting situations transparently. Employing this model, we show that vibronic coupling effects play a crucial role even when a single E degenerate eigenstate of the system supports the current. The maximum current of a degenerate eigenstate depends on the strength of the nonadiabatic interactions. In the limit of large nuclear to electronic masses, in which the Born–Oppenheimer approximation becomes exact, constant ring currents and time-averaged oscillatory currents necessarily vanish.

Dynamical Jahn-Teller effects on the generation of electronic ring currents by circularly polarized light

“…From a theory perspective, it is well understood that circularly polarized light can also trigger ring-currents by resonantly exciting the electrons to a manifold of doubly-degenerate electronic states of (E) symmetry related to a symmetry axis of the molecule [4,[8][9][10][11][12]. It is inevitable by symmetry, though, that the (E × e) Jahn-Teller (JT) effect couples the (E) electronic states and (e) vibrational modes in all molecular point groups able to support ring currents [13][14][15][16], thus potentially mixing the two pristine ring-current circulation directions defined in the uncoupled limit [17,18]. The role of the (E × e) JT effect and related vibrationalelectronic (vibronic) coupling terms is well established in the areas of electronic spectroscopy [19,20], ultrafast vibronic dynamics [21,22] and charge migration [23].…”

“…These are, for example, the (E 1u ) and (E u ) representations in the D 6h and D 4h point groups of benzene [12] and porphyrins [27], respectively. Therefore, one-photon electronic transitions from the totally symmetric ground-electronic state to the (E) states are allowed and the interaction of the molecules with circularly polarized light in the molecular (x, y)-plane can generate ring currents owing to angular momentum conservation in the photo-absorption process [17,32].…”

“…Dipolar transitions from the ground electronic state fulfill the selection rule ∆q = ±1 and circularly polarized radiation can only induce transitions (0 ↔ 1) for LCP and (0 ↔ −1) for RCP [17]. Finally, the vibronic eigenstates |j q of the complete Hamiltonian (7) in the q = 1 block are one-to-one degenerate with the eigenstates of the q = −1 block.…”

Polariton ring currents and circular dichroism of Mg-porphyrin in a chiral cavity

“…These results clearly demonstrate the utility of chiral cavities to manipulate photochemical processes of molecules. Future extensions of this study include incorporating the vibronic coupling, 58–60 cavity leakage, and many-molecule collective dark states 29 into the model. The chiral cavity-induced time reversal symmetry breaking may also be employed to create topological states.…”

Coherent ring-current migration of Mg-phthalocyanine probed by time-resolved X-ray circular dichroism

“…1,2,[16][17][18][19] In this theoretical study, we focus on the CPL induced ring currents, which are receiving considerable attention. 11,[20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] The sense of the resulting ring current is determined by the circular polarization of the pulse. Furthermore, CPL can create ring currents in selected states by tuning the pulse frequency to specic electronic states.…”