Quantum vibrational nano-imaging; a molecular ruler to image structure, coupling, and disorder in molecular materials

Properties and functions of molecular materials often emerge from intermolecular interactions and associated nanoscale structure and morphology. However, defects and disorder disturb from energy conversion to carrier transport. Conventional microscopy techniques lack spatial resolution and sensitivity to the low-energy scales of intermolecular interactions and intra-molecular energy relaxation. We address these problems in novel combinations of spatio-spectral and spatio-temporal infrared nano-imaging. Here, coupling between molecular vibrations leads to collective modes, with distinct spectral features sensitive to intermolecular distance and relative molecular orientation. Resolving this vibrational exciton formation as a molecular ruler in IR nano-spectroscopy, we image competing phases and local disorder in molecular solids – information inaccessible by conventional X-ray or electron-based crystallography. In the application to the growth of porphyrin model organic electronic nanocrystals we observe the evolution of defects in competing amorphous and crystalline phases with nanometer spatial resolution [1,5]. Similarly, imaging vibrational coupling in polymers [2] and molecular monolayer [3], we resolve domain formation from the molecular to nano-scale. Further, in another modality through mode selective coupling of vibrational resonances to IR nano-antennas and associated Purcell-enhanced modification of vibrational lifetimes, we resolve intramolecular vibrational interaction and vibrational energy redistribution (IVR) [4]. I will summarize with a perspective for nm-fs resolved precision vibrational nano-spectroscopy for functional imaging in the low-energy landscape of molecular matter.

[1] Muller, et al., PNAS 117, 7030 (2020);

[2] Gray, et al., Nano Lett. 21, 5754 (2021);

[3] Dönges et al. Nano Lett. 21, 6463 (2021);

[4] Wilcken et al. PNAS 120, e2220852120 (2023);

[5] Puro, et al. 24, 1909 (2024).