Interactive photochemistry / A conceptual laboratory
Follow nuclear motion across electronic-state surfaces. Choose a pathway, rotate the landscape, and step through the science.
Drag to orbit · arrow keys also rotate · the marker represents nuclear configuration, not an electron.
Playback seconds are not molecular time. These are original analytical surfaces and prescribed paths, not calculated PESs, propagated wavepackets, rate predictions, or surface-hopping trajectories.
Franck–Condon absorption is drawn vertically: electronic excitation is fast relative to nuclear motion. Fluorescence returns an excited singlet to the ground singlet with photon emission. Vibrational energy can subsequently relax to the surroundings.
Intersystem crossing transfers population between states of different multiplicity. The displayed crossing uses spin-diabatic singlet/triplet surfaces; spin–orbit coupling is not explicitly modelled. T₁ → S₀ phosphorescence is radiative and spin-forbidden in the pure-spin limit.
A same-spin conical intersection has two independent degeneracy-lifting directions. This close-up uses idealized orthogonalized branching-plane coordinates g and h; the remaining seam coordinates are suppressed.
Timescales & lifetimes
For a simple first-order excited-state population, τ = 1 / Σk. Fluorescence, internal conversion, intersystem crossing, and other competing channels all affect the observed lifetime. The radiative lifetime 1/kᵣ is generally different from the measured population lifetime.
The player uses labelled illustrative values when explaining emission: 5 ns for a singlet population and 1 ms for a triplet population. These are teaching examples, not measurements for your crown ethers, and are not inferred from the model surfaces. Absorption, relaxation, ISC, and CI-transfer times are left system-dependent.
Emission landscapes: S₀ = 0.35(x + 1)² + 0.25y²S₁ = 3 + 0.35(x − 0.8)² + 0.30y²T₁ = 2.8 + 0.30x² + 0.30y² At y = 0 the singlet/triplet crossing on the displayed path is x ≈ 0.817. The triplet minimum is displaced from the ground-state minimum so absorption and phosphorescence occur at different geometries. These are illustrative model choices, not a universal geometry relationship. Radiative transitions preserve the nuclear coordinates in this illustration.
Local intersection model: E± = 2 + 0.30(g² + h²) + t·g ± √(g² + h² + δ²) Peaked: t = 0, δ = 0. Sloped: t = 1.4, δ = 0. Gapped comparison: t = 0, δ = 0.35. The last choice removes the degeneracy in this displayed slice and is not a CI. The regularizing quadratic term is an illustrative extension away from the local intersection, not a molecular fit.
The CI journey shows passage through degeneracy and prescribed outgoing directions. In the gapped comparison it follows the upper surface continuously. Actual transfer probabilities, wavepacket splitting, product identities, and branching ratios require dynamics and molecular information.
Explore the crown ether and excited-state studies that motivate this illustration.
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