How Symmetry Governs the Dihedral Angle Dependence of Intermolecular Spin–Orbit Coupling

Spin–orbit, charge-transfer intersystem crossing (SOCT-ISC) allows for the efficient production of triplet excited states in donor–acceptor (DA) dyads without the involvement of heavy atoms, for use in a myriad of technologies. This process is commonly believed to proceed optimally when the donor and acceptor moieties are oriented under an orthogonal dihedral angle. Here, we challenge this idea through a theoretical study unveiling an orthogonal scenario where spin–orbit couplings (SOCs) are minimized. This is rationalized based on an analysis of the structure-imposed symmetry properties of the involved singlet and triplet states. Notably, in this scenario, finite SOCs demand oblique orientation angles, which in turn requires molecular chirality, suggesting chirality to be a prerequisite for activating the associated SOCT-ISC pathways.

pubs.acs.org

Excited-State Symmetry Breaking Dynamics Driven by Mode-Resolved Jahn–Teller Distortion in Luminescent Tris(2,4,6-trichlorophenyl)methyl Radicals

Understanding the electronic excited-state dynamics of luminescent tris(2,4,6-trichlorophenyl)methyl (TTM) radicals is important for optimizing them as optical-spin interfaces for quantum information applications. Symmetric TTMs possess degenerate lowest-energy excited states for which the ultrafast photophysics remains unexplored. Here, we use broadband transient absorption (BBTA) spectroscopy on these systems at cryogenic temperatures to provide insight into their complex ultrafast electronic state relaxation via Jahn–Teller (JT) distortion and solvent stabilization. Global lifetime fitting of time-dependent BBTA spectra shows a 421 ± 15 fs JT distortion in TTM followed by a 13.9 ± 0.1 ps stabilization of the symmetry-broken relaxed excited state geometry of the radical by the solvent. Coherent wavepacket dynamics reveal fast dephasing of low frequency vibrations and a growth of coherent oscillations associated with an 807 cm–1 mode with a time constant of ∼485 fs, matching the JT distortion time scale. Electronic structure calculations reveal a conical intersection, while Huang–Rhys factor calculations exhibit significant vibronic coupling, thus corroborating the experimental results. Manifestation of similar vibronically coupled excited-state symmetry breaking was also found in a series of 4-aryl-substituted TTM derivatives and verified by complementary theoretical calculations.

pubs.acs.org

Photophysics of Iodine-Substituted Oxyluciferins: Observation of Simultaneous High Fluorescence Quantum Yields and Singlet Oxygen Sensitization

The bioluminescence of firefly oxyluciferin is a subject of broad interest, but while its photophysics have been extensively studied within the singlet manifold, little is known about its ability to p...

pubs.acs.org

QC Lab: A Python Package for Quantum–Classical Dynamics

QC Lab is an open-source Python package for quantum–classical (QC) dynamics simulations aimed to promote the development of QC algorithms, and their application to a wide variety of relevant model problems. It follows a modular design that facilitates cross-compatibility between algorithms and models. By decomposing algorithms and models into a series of tasks and ingredients that can be substituted and reused, it minimizes development efforts and code redundancy. In this Paper, we introduce the first stable version of QC Lab, and describe its design philosophy.

pubs.acs.org

Optically Addressing Circularly Polarized Vibrations in Molecules

Circularly polarized (CP) vibrations are the nuclear-motion analog of CP light, emerging in molecules with non-Abelian point-group symmetry that support orthogonal and degenerate vibrational normal mo...

pubs.acs.org

Differential absorption of circularly polarized light by a centrosymmetric crystal

Crystalline solids are governed by universal structure-property relationships derived from their crystal symmetry, leading to paradigmatic rules on what properties they can and cannot exhibit. A long-...

science.org

Mixed quantum–classical dynamics yields anharmonic Rabi oscillations

We apply a mixed quantum–classical (MQC) approach to the quantum Rabi model, involving a classical optical field coupled self-consistently to a quantum two-leve

pubs.aip.org

Molecular engineering charge transfer and triplet exciton formation in donor–acceptor cocrystals

Organic donor–acceptor (D–A) cocrystals are gaining attention for their potential applications in optoelectronic devices. This study explores the dynamics of ch

pubs.aip.org