Notes on molecules, models, and computation.
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How the donor closes the gap: para-substituent effects in a minimal push-pull dye
A four-point series of para-X-benzylidenemalononitriles (X = H, F, NH₂, NMe₂) shows how donor strength moves the HOMO and LUMO, and explains why para-fluorine acts as a weak net donor in this minimal push-pull scaffold.
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Does Hillel's 2024 push-pull sentence hold for 4-dimethylamino-4′-nitroazobenzene?
An independent RKS/UKS B3LYP-D3(BJ)/cc-pVDZ CNNC torsion scan of an untested 2024 generalization — that push-pull azobenzenes, like protonated AzPyH+, would lose the S0/T1 crossing along the azo twist. The test case is 4-dimethylamino-4′-nitroazobenzene, with azobenzene, AzPy, AzPyH+, and 2-phenylazopyridine as controls.
How the donor closes the gap: para-substituent effects in a minimal push-pull dye
A four-point series of para-X-benzylidenemalononitriles (X = H, F, NH₂, NMe₂) shows how donor strength moves the HOMO and LUMO, and explains why para-fluorine acts as a weak net donor in this minimal push-pull scaffold.
How the acceptor closes the gap: acceptor-strength effects in para-methoxy push-pull dyes
A three-point series of para-methoxy push-pull dyes with CN, DCV, and TCF acceptors shows how acceptor strength moves the HOMO and LUMO, and how the HOMO-LUMO gap closes as the acceptor strengthens.
One dye, one transition: how DCDHF-Me2 earns the two-level picture
The blinking-to-absorption note modeled a fluorescent dye as two levels and named what that hides. Computing the actual excited-state manifold of DCDHF-Me2 — a push-pull dye engineered for single-molecule imaging — gives a sharper answer than we planned. Its visible absorption is essentially one transition, and the rest of the manifold lives in the deep UV; benzene, the dye's own parent ring, shows the opposite arrangement for a reason symmetry makes plain.
From blinking to absorption: how one molecule becomes a spectrum
A single fluorescent molecule blinks; a cuvette full of the same molecules gives a smooth absorption band. The two pictures are the same Jablonski diagram read at different scales — one molecule versus an ensemble, one photon at a time versus a steady-state rate. This post traces the path from quantized absorption and emission events to a bulk spectrum, and extends the same diagram to two-photon absorption as the nonlinear version of the same transition.
Extending Villatoro et al.'s SIREN benchmark: the momentum recovery region
An independent extension of Villatoro, Geraci, and Schiavazzi's 2026 multi-fidelity SIREN benchmark maps, as a function of the heavy-ball momentum coefficient, the set of learning rates at which the described SIREN convention reaches the official convention's error floor.
One muon, two frames, and the workflow that parked itself
A minimal muon time-dilation calculation was pushed through a preregistered, multi-role research workflow as an acceptance trial. The two frames agreed exactly as they must; the workflow coordinated every step, then parked itself over a figure label. This note explains both machines.
Why some atoms cost more than their neighbors
A fixed atomic calculation separates the cost of how an atom is represented from the cost of getting its self-consistent field to settle.
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