Superfluorescent squaraine with efficient two-photon absorption and high photostability

The synthesis, linear photophysical, two-photon absorption (2PA), femtosecond transient absorption, and superfluorescence properties of a new symmetrical squaraine derivative (1) are reported. Steady-state linear spectral and photochemical properties, fluorescence lifetimes, and excitation anisotropy of 1 were investigated in various organic solvents. High fluorescence quantum yields (≈0.7) and very high photostability (photodecomposition quantum yields ≈10^-6-10^-8) were observed. An open-aperture Z-scan method was used to obtain 2PA spectra of 1 over a broad spectral range (maximum 2PA cross section ≈1000 GM). Excited-state absorption (ESA) and gain was observed by femtosecond transient absorption spectroscopy, in which both reached a maximum at approximately 500 fs. Squaraine 1 exhibits efficient superfluorescence. The quantum chemical study of 1 revealed the simulated vibronic nature of the 1PA and 2PA spectra were in good agreement with experimental data; this may provide the ability to predict potential advanced photonic materials. Super fluoro to the rescue! Large two-photon absorption (2PA), femtosecond transient absorption kinetics, and efficient superfluorescence properties of a new symmetrical squaraine derivative (1) are reported along with extremely high photochemical stability. The density functional theory (DFT)-based quantum chemical study of 1 reveals the vibronic nature of the 2PA spectra in the main linear absorption band that is in good agreement with experimental data.