Measured linear spectroscopy and absolute multiphoton-excited fluorescence, supported by quantum-chemical calculations, relate electron-donating branch geometry in three diquinoxalines to two- and three-photon absorption. DQ-DPA engages four electronically active branches and reaches 230 ± 50 GM in its lowest-energy two-photon band, compared with two active branches and approximately 110–120 GM for DQ-IMD and DQ-DDA. All three initiate fabrication of fluorescent 3D microstructures in an acrylic resin. The additive branch interpretation is supported by orbital calculations; the demonstrated app

An interactive research companion

A molecule’s shape can open new paths for absorbing light. Follow three molecular designs from moving electrons to fluorescent, three-dimensional microstructures.

Choose a molecule. Tune the light. Try to write.

Different electron-donating branches on the same diquinoxaline core.

Largest measured lower-energy two-photon absorption band, in DQ-DPA.

Real microstructures written by two-photon polymerization, with intrinsic fluorescence.

01 / MOLECULAR ARCHITECTURE

Four branches. How many are connected?

All three molecules carry four electron-donating branches around an electron-accepting core. But geometry determines how many branches join the electronic delocalization. Switch the molecule to reveal the paths.

Choose your photoinitiator

active branchesout of four donating branches

Emission peak in DCM

Fluorescence quantum yield in DCM

The axial branches participate most strongly. The other two are weakly involved in electronic delocalization.

Measured absorption: Tables 3 and 4. Emission in dichloromethane (DCM): Table 1. Active pathways: quantum-chemical interpretation in Sections 2.2–2.3 and Figure 3; the drawing simplifies the chemical structures.

The absorption cross-section measures how readily a molecule absorbs two photons; GM is the standard unit. Normalized by the active branch count, the lower-energy response is about 58 ± 6 GM per branch. DQ-DPA’s more planar conformation allows all four branches to contribute.

DQ-DPA absorbs two photons most strongly in this band; DQ-IMD has the highest fluorescence quantum yield in DCM. These are distinct molecular properties.

The ground state and initial excited state are nearly symmetric and quadrupolar. As the excited molecule relaxes, its charge distribution becomes asymmetric and dipolar. Solvent-dependent fluorescence and quantum-chemical calculations support this symmetry-breaking interpretation (Section 2.2).

02 / THE LIGHT GATE

Two photons meet. A small volume responds.

Two-photon absorption rises roughly with the square of light intensity . At a tightly focused beam, that makes excitation concentrate near the focus. Move the intensity slider to see why this is useful for writing inside a resin.

The intensity multiplier

Increase intensity and watch the response grow faster than the beam itself. A third photon makes the power dependence steeper.

The paper’s measured log–log slope was 2.1 ± 0.1 for two-photon excitation.

Section 2.3 and Supporting Information SI4, Figure SI5. The visualization uses ideal I² or I³ scaling and a normalized Gaussian beam; it does not predict voxel dimensions.

03 / THE WRITING EXPERIMENT

Can you cross the writing threshold?

The authors mixed these molecules into two acrylic resins and wrote real 3D structures. Here, adjust the concentration and light fluence to reach the point where a solid structure can form. Then reveal its fluorescence.

Write a fluorescent microstructure

Rotate the view

Tip: more initiator lowers the threshold. Above about 0.18 wt%, the measured benefit nearly levels off.

Fabrication details: Supporting Information, Section SI6, pp. 17–18. Supplementary methods ↗.

Threshold model: linear interpolation between approximate concentration–fluence values in Section 2.4 and Figure 6a (0.05 → 0.0030, 0.13 → 0.0015, 0.18–0.22 → 0.0013 J/cm²). The same representative curve is used for all three molecules, which performed comparably. Geometry, writing speed and glow are conceptual; solution quantum yields do not determine the rendered brightness.

04 / BACK TO THE EXPERIMENT

What the researchers actually made.

The study joins photophysical measurements and electronic-structure calculations to a fabrication test. These microscopy images show real 3D microstructures , made with the diquinoxalines as photoinitiators.

A printed structure that keeps a molecular glow.

Microstructures were fabricated at about 0.22 wt% photoinitiator and about 13 GW/cm². Residual molecules that were not activated during polymerization retain their emissive properties inside the printed material.

The microscopy demonstrates structurally intact, fluorescent microstructures. The combination suggests future uses in high-resolution displays, 3D data storage, anticounterfeiting and tunable-emission devices.

The central connection is between molecular conformation, multiphoton absorption and practical polymerization.

Figures 1, 3, 5 and 6 reproduced from Valverde et al., under CC BY 4.0. Figures are unchanged apart from display size. The source’s Supporting Information provides synthesis, spectroscopy, quantum-chemical calculations and two-photon fabrication methods.

Continue the discovery

From a molecular choice to a material possibility.

The paper explains why more planar donor branches can give a stronger two-photon response, and tests these molecules by fabricating emissive 3D microstructures. It connects fundamental photophysics with photoinitiator design.

The research paper

Valverde et al. · ACS Physical Chemistry Au 6 (2026), 803–814

Paper credit · João V. P. Valverde, Welisson de P. Silva, Daniel L. Silva, Nícolas O. Decarli, Mieczysław Łapkowski, Leonardo De Boni and Cleber R. Mendonça. DOI: 10.1021/acsphyschemau.6c00035. © 2026 The Authors. Published by the American Chemical Society. Licensed under CC BY 4.0.

Illustration and models · The graphical abstract is an AI-generated conceptual illustration informed by the paper. Interactive molecular pathways and microstructure geometry are educational adaptations. Measured values, calculated interpretations and proposed applications are identified in the companion.

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