Fig. 3: Vibronically driven intramolecular dynamics in quadrupolar dyes.

a,b, Two-dimensional electronic spectroscopy maps of the A–D–A molecule in CHX (a) and DCM (b) at selected waiting times (T) of 10 fs and 800 fs. At early times, the 2DES maps reveal a pronounced vibronic peak structure (black circles) arising from vibrational wavepacket motion on the \(\left|{S}_{1}\right\rangle\) PES dominated by the symmetric C–C stretching mode. The early time maps are very similar in both solvents. At later times, washout of the vibronic peaks leaves a broad stimulated emission peak from \(\left|{S}_{1}\right\rangle\) in CHX, whereas in DCM excited-state absorption from \(\left|{S}_{1,{\rm{Rel}}}\right\rangle\) builds up. c,d, Residual differential transmission ΔT/T maps at early times in CHX (c) and DCM (d) obtained by subtracting the long-lived components (blue, black and red in Fig. 2e–h) from the corresponding ΔT/T maps in Fig. 2c,d. d, In DCM, polar solvation gives rise to a red-shifting stimulated emission (d, black arrow) at energies below 2 eV, which is absent in CHX (c). The black arrow in d is a guide to the eyes. Further subtraction of the solvent-induced component (orange in Fig. 2f,h) from the DCM map uncovers vibronic lineshapes and sub-50 fs dynamics similar in both solvents (insets). This suggests that these initial dynamics are mainly governed by intramolecular vibronic couplings while the solvent polarity has minor effect.