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.

Ultrafast excited state dynamics of dinaphthoporphycenes were investigated using femtosecond and picosecond degenerate pump-probe techniques at 600 nm and 800 nm, respectively. Femtosecond pump-probe data indicated photo-induced absorption at 600 nm resulting from two-photon/single photon excitation, whereas picosecond pump-probe data demonstrated photo-bleaching which was a consequence of three-photon absorption. The fastest lifetimes (100-120 fs) observed are attributed to the intramolecular vibrational relaxation, the slower ones (1-3 ps) to internal conversion, and the slowest components (7-10 ps) to non-radiative decay back to ground state. Z-scan studies in the 560-600 nm range were also carried out. V

Sterically hindered molecules like the title compounds, combined with their strong NLO coefficients make them potential candidates for photonic applications.

No abstract

No abstract

No abstract

Enhancing the nonlinear absorption in hydrogen exfoliated graphene using metal oxide nanoparticle functionalization.

Zinc phthalocyanine with S-aryl groups at α-positions have been synthesized and its optical, emission, electrochemical and third-order nonlinear optical properties were investigated. Both the Soret and Q-bands were red-shifted and obeyed Beer–Lambert's law. Electrochemical properties indicated that both oxidation and reduction processes were ring centered. Emission spectra were recorded in different solvents and the fluorescence yields obtained were in the range of 0.02 while time-resolved fluorescence data revealed lifetimes of typically few ns. Excited state dynamics in this novel thio-zinc phthalocyanine molecule has been investigated using femtosecond (fs) degenerate pump-probe spectroscopy. Nonlinear optical properties of this molecule have been examined using the Z-scan technique with picosecond (ps) and fs pulses. Both open and closed aperture Z-scan curves were recorded with ~2 ps/~150 fs laser pulses at a wavelength of 800 nm and nonlinear optical coefficients were extracted from both the studies. Degenerate pump-probe data performed at 600 nm suggested a single long lifetime of ~300 ps, possibly originating from the non-radiative decay of S1 state.