Dyes, excited-state absorption

Keywords Cyanine dyes Excited state absorption Polymethine dyes Pump-probe Two-photon absorption Z-scan... 

Padilha LA, Webster S, Hu H, Przhonska OV, Hagan DJ, Van Stryland EW, Bondar MV, Davydenko IG, Slominsky YL, Kachkovski AD (2008) Excited state absorption and decay kinetics of near IR polymethine dyes. Chem Phys 352 97-105... 

Unfortunately there are no experimental results which could be compared with these theoretical curves. All experiments reported in the literature are either made with cyanine dyes showing some excited state absorption or with phthalocyanine dyes which have an extremely high intersystem crossing rate so that triplet populations cannot be neglected. 

A quantitative description of giant pulse generation is again given by a set of rate equations in the simplest case one for the inversion, another for the population density mo of the dye in the ground state So and a third for the laser light intensity nc. If excited state absorption has to be taken into account, additional rate equations would have to be added as described above in the section on nonlinear absorption. 

The above discussion of the Q-switching process immediately gives some requirements for a good Q-switching dye. First, this dye must exhibit a saturable absorption at the laser wavelength. Second, the residual losses by excited state absorption should be as low as possible. Third, the photochemical stability (and, of course, also the chemical stability in the dark) should be as high as possible. Fourth, the... 

Earlier studies on dye-sensitized Ti02 reported nanosecond time constants for the injection kinetics [16, 40-42]. These results were obtained indirectly from the measurement of the injection quantum yield and implicitly assumed that the interfacial electron transfer reaction was competing only with the decay of the dye excited state. Other studies were based on the same assumption but used measurements of the dye fluorescence lifetime, which provided picosecond-femtosecond time resolution [43-45]. Direct time-resolved observation of the buildup of the optical absorption due to the oxidized dye species S+ has been employed in more recent studies [46-51]. This appears to be a more reliable way of monitoring the charge injection process as it does not require any initial assumption on the sensitizing mechanism. 

CHjCl show that 0 > 0.5. Excited state absorption data in laser dyes at the XeCl wavelength have also been published. ... 

Absorption spectra and decay kinetics of electron adducts of proflavin and acridine yellow in aqueous solution have been studied and the rates of transfer to different electron acceptors measured.Electron injection from xanthene dyes and tetraphenylporphines into ZnO and TiO has been shown to compete with fluorescence.Picosecond spectroscopy has been used to determine excited-state absorption spectra and decay mechanisms in photostabilizers.Fluorescence... 

Fig. 2 Potential energy diagram of DSSC. For net forward electron transfer the oxidation potential of the dye-excited state, D /D+ should be higher than the semiconductor conduction band, and the redox potential of the hole conductor should be higher than the dye-ground state potential D/D+. Absorption of light by the dye causes charge separation across the interface, resulting in a splitting of the electrochemical potential and hence a photovoltage.

Transient Absorption Time-re-solved absorption can be used to monitor the appearance or disappearance of the reduced or oxidized states of molecular species. Ultra fast time-resolved absorption was first used by Tachibana and coworkers to measure the rate of injection from dye-excited state into semiconductor, probing the absorption of the... 

D.J. Bradley, P. Ewart, J.V. Nicholas, J.R.D. Shaw Excited state absorption spectroscopy of alkaline earths selectively pumped by tunable dye lasers. I. Barium arc spectra. J. Phys. B6, 1594 (1973)... 

The photcwurrent measurements establish that injection of charges occurs from the excited state of the dye to the conduction band of the semiconductor, but does not say anything about the identity of the dye excited state involved. Luminescence and time-resolved (transient) absorption studies on dye-semiconductor colloids and dye-coated films on conducting glass electrodes have been useful to establish the identity of the excited state and energetics of the sensitization process. 

Fig. 1. Schematic energy-level diagram for a dye molecule. Electronic states Sq = ground singlet state = first excited singlet state S2 = second excited singlet state Tj = first excited triplet state T2 = second excited triplet state EVS = excited vibrational states. Transitions A = absorption excited states ...

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