The broadband reverse absorption in a multi-branched conjugated compound TPPh is investigated. Transient absorptive spectra of TPPh solution is recorded and a broadband excited-state absorption (475~780 nm) is discovered. The lifetime of this broadband excited-state absorption was measured to be about 20 ns. Transient fluorescence experiment was conducted to confirm that the long-lived broadband excited-state absorption is established on the first singlet state. Optical limiting with extremely high linear transmittance is achieved under the excitation of 532 nm, 21 ps pulses. Theoretically analysis showed that both two-photon absorption and excited-state absorption played a part in it, optical limiting capability is thus enhanced via cooperating effects of two-photon absorption and excited-state absorption. All of the findings suggested that TPPh is a good broadband nonlinear absorptive material and could be further optimized for optical limiting applications.
Meso-tetrakis(4-cyanophenyl)N-confused porphyrin [NCTPP(CN)4] and its two metallized derivatives with Cu2+ and Zn2+ ligand in the central position of the macrocycle are synthesized and spectroscopically characterized. Their excited-state dynamics are investigated with transient absorption (TA) spectroscopy upon excitation by 190 fs laser pulses at 420 nm within their Soret band region. A global and target analysis for the TA spectra of each porphyrin is performed via a four-level model including singlet (S) and triplet (T) states to extract the photophysical parameters at a variety of absorption wavelengths. Furthermore the corresponding excited-state lifetimes are extracted and discussed.