Ultrafast Dynamics of Nile Red Interacting with Metal Doped Mesoporous Materials

We report on ultrafast studies of Nile Red (NR) interacting with MCM41 mesoporous materials doped by Al, Ga, Zr, and Ti in dichloromethane suspensions. The steady-state results showed a significant red shift and broadening of the diffuse transmittance and the emission spectra upon interaction with the MCM41-based materials. These findings are explained in terms of H-bonds with the host, different Brønsted/Lewis interactions with the matrix and formation of H- and J-aggregates, in addition to weakly and strongly adsorbed monomers. The pico- to nanosecond time-resolved data support this explanation, showing a significant shortening in the emission lifetimes where NR is interacting with metal-doped MCM41. The femtosecond dynamics of NR loaded into X-MCM41 (X = Si, Al, Ga) indicate that the charge-separated state (CS) is formed at the S1 state in ∼350 fs. For Zr- and Ti- MCM41 hosts the intramolecular charge transfer (ICT) occurs in less than 200 fs, and a subsequent electron injection to Ti or Zr trap states happens in ∼250 fs. Our studies reveal a strong interaction between the NR species and the framework of MCM41 materials at both the S0 and S1 states.