Ultrafast electronic dynamics and vibrational dynamics of SWCNT under alkylation and annealing

Using ultrashort visible pulse laser, we have performed transient absorption spectroscopy to study the electronic relaxation and vibrational dynamics for three SWCNT samples of non-substituted SWCNT, alkylated SWCNT, and annealed alkylated SWCNT. Estimated lifetimes of ∼100 fs and ∼1 ps can be assigned to intraband and interband relaxation processes, respectively. Compared with the non-substituted sample, the intraband transition rate was found to be 7% smaller for the alkylated sample and nearly equal to the annealed alkylated sample within 2%. It implies that the intraband relaxation rate is not affected by alkylation itself but inhibited by excess chemical modification. Conversely, the interband relaxation rate shows no difference between the three samples. Short-time Fourier transform analysis of the measured traces of pump–probe delay dependent difference absorbance visualizes the change of molecular vibration frequency reflecting the energy transfer from (6,5)-SWCNT to (6,4)-SWCNT and the molecular structure change during the interband transition.