Ultrafast Excited-State Dynamics and Dispersion Studies of Third-Order Optical Nonlinearities in Novel Corroles

Abstract

Ultrafast nonlinear optical (NLO) properties of four novel Corroles in the visible spectral range (660–800 nm) were evaluated using picosecond Z-scan technique. Ultrafast excited state dynamics have also been appraised with picosecond (ps) and femtosecond (fs) degenerate pump–probe techniques using excitation wavelengths of 800 and 600 nm, respectively. The excitation by 800 nm photons resulted in two-photon absorption at adequately high peak intensities, thereby facilitating the access to higher excited states (S n ). The nonradiative relaxation mechanisms from these states, reflected in the pump–probe data, consisted of double-exponential decay with a slow component in the range of 54–277 ps and faster component in the range of 2.0 to 2.5 ps. When excited with 600 nm photons (unfocused), photoinduced absorption was observed with the first excited state S1 being populated, and as a consequence single decay was observed in the data of all molecules studied. These retrieved lifetimes were analogous to those obtained with picosecond pump–probe data. The long lifetime is attributed to nonradiative decay from the S1 state with possible contribution from triplet states, whereas the shorter lifetime is attributed to the internal conversion (S2 to S1*), followed by vibrational relaxation (S1* to S1) processes. Time-resolved fluorescence lifetime measurements revealed the magnitude of radiative lifetimes to be in the nanosecond regime. NLO coefficients were evaluated from the Z-scan data at wavelengths of 660, 680, 700, 740, and 800 nm. Large two-photon absorption coefficients (β)/cross-sections (σ2) at 740 nm/680 nm were recorded for these molecules, making them apposite for applications such as two-photon induced photodynamic therapy and lithography. Figure of merit, T, was <1 for all molecules at 740 and 800 nm, suggesting that these molecules find use in photonic device applications.

Femtosecond to Microsecond Dynamics of Soret-Band Excited Corroles

“…For the fitting, we used the k f (fluorescence rate constant) from the fluorescence lifetime data presented in our earlier reports. 32 Further, we used the triplet lifetime data from the ns-TA kinetics for the rate-constant k 4 and fixed it for fitting procedure. Figure 12 shows the global fitting of the TA spectra recorded for Ge-TTC.…”

Photophysical properties of electron-deficient free-base corroles bearing meso-fluorophenyl substituents

“…39 They attributed the 2.4 ps decay to the S 2 →S 1 * process. Baskin et al have estimated that vibrationally excited Soret→Q y , Q x and Q y →Q x electronic relaxation occurs in less than 100 fs for H 2 TPP by the femtosecond upconversion fluorescence method, following excitation at 398 nm in benzene.…”

Ultrafast Dynamics of SI-GaAs and LT-GaAs by Degenerate Pump-Probe Studies

“…The PDPP measurements [1] were performed using 800 nm, 1 kHz pulses (Figure 1(a)). Figure1(b) shows the typical pump probe reflectivity measurements of LT-GaAs and SI-GaAs at 800 nm pulses achieved with average energy of 10 µJ/pulse.…”