Fig. 2: Ultrafast dynamics in non-polar and polar solvents.

a,b, Experimental and simulated linear absorption (red) and photoluminescence (black) spectra of the A–D–A molecule dissolved in non-polar CHX (a) and polar DCM (b). c,d, Differential transmission ΔT/T maps of the molecule in CHX and DCM. A persistent ground-state bleaching band around 2.1 eV monitors \(\left|{S}_{0}\right\rangle \to \left|{S}_{1}^{* }\right\rangle\) transitions. c, In CHX, a long-lived band below 2 eV probes stimulated emission from the relaxed excited state \(\left|{S}_{1}\right\rangle \to \left|{S}_{0}\right\rangle\). d, In DCM, this stimulated emission transiently red-shifts and decays within ~400 fs (\(\left|{S}_{1,{\rm{Sol}}}\right\rangle\)) while, concurrently, absorption from the solvated excited state (\(\left|{S}_{1,{\rm{Rel}}}\right\rangle\)) builds up. In both solvents, the dynamics are modulated by persistent ~1,430 cm⁻¹ C–C stretching oscillations. e,f, Incoherent spectral components of the ΔT/T in CHX (e) and DCM (f) deduced by a global analysis of the ΔT/T data in c and d, respectively. g,h, Population dynamics corresponding to the spectra in e and f, respectively. The dynamics are normalized to the total population of the excited state.