Probing intramolecular vibronic coupling through vibronic-state imaging

Abstract

Vibronic coupling is a central issue in molecular spectroscopy. Here we investigate vibronic coupling within a single pentacene molecule in real space by imaging the spatial distribution of single-molecule electroluminescence via highly localized excitation of tunneling electrons in a controlled plasmonic junction. The observed two-spot orientation for certain vibronic-state imaging is found to be evidently different from the purely electronic 0–0 transition, rotated by 90°, which reflects the change in the transition dipole orientation from along the molecular short axis to the long axis. Such a change reveals the occurrence of strong vibronic coupling associated with a large Herzberg–Teller contribution, going beyond the conventional Franck–Condon picture. The emergence of large vibration-induced transition charges oscillating along the long axis is found to originate from the strong dynamic perturbation of the anti-symmetric vibration on those carbon atoms with large transition density populations during electronic transitions.

Toward a BT.2020 green emitter through a combined multiple resonance effect and multi-lock strategy

“…It is known to us that the electron-vibration coupling dominates the FWHM of the emission band when large-amplitude nuclear rearrangement in the S1 state has been suppressed. [10][11][12][13] To better understand the excellent color purity achieved by the tCzphBs, the vibrationally-resolved fluorescence spectra were simulated by TD-DFT at the PBE0/6-31g (d, p) level and compared with DtBuCzB (Fig. 3c, 3d, and Supplementary Fig.…”

“…Therefore, we believe that this multi-lock strategy for MR-TADF materials could be used for the development of narrowband organic emitters with full-color emissions, as well as high EL efficiency and stability. The 1 H and 13 C NMR chemical shifts were expressed as δ downfield using tetramethylsilane (TMS) as internal reference. Mass spectra were recorded by Thermo Scientific ISQ TM EC single quadrupole mass spectrometer using positive ion electrospray ionization (ESI).…”

“…Generally, the emission spectra of fluorescent molecules are broad due to structural deformation in the excited state and the molecular vibrations, [7][8][9][10][11][12] which are enhanced by thermal conductivity through conjugated π-bonds. 13,14 Recently, Hatakeyama et al reported on a new kind of thermally activated delayed fluorescence (TADF) emitters based on multiple-resonance (MR). [15][16][17] The separation of the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbitals at the atomic level resulted in small singlet-triplet exchange energy, 18 as well as suppressed thermal conductivity in the excited state.…”

High-resolution vibronic spectroscopy of a single molecule embedded in a crystal

“…In addition, accurate values of the simulated wavenumbers require mode-specific correction terms. Besides conformational changes, one might consider a redistribution of intensities between vibronic lines caused by 13 C substitution of individual carbon atoms in DBT and by Herzberg-Teller effects 56,[89][90][91] . The probability of 13 C substitution is about 28% in a DBT molecule and the effect on the vibronic spectrum depends on the exact substitution site.…”

Electric Field Controlled Single-Molecule Optical Switch by Through-Space Charge Transfer State

“…One of the most important goals in nano-optics is to build nanoscale molecular switches with controlled photon emissions. , Such functional optical devices possess great application potentials in areas ranging from optical data storage/memories to nanoscale light sources. − The developments of experimental techniques have made it possible to build actual nanodevices with single molecules as functional units. , Especially, it has been shown that the tunneling electrons in biased metallic junctions such as in a scanning tunneling microscope (STM) could be applied to induce electroluminescence (EL) from single molecules. ,− These advanced techniques thus opened the door for the design and validation of single-molecule based optical switches at the nanometer scale.…”