Steady-state absorption and emission

Seminal studies on the dynamics of proton transfer in the triplet manifold have been performed on HBO [109]. It was found that in the triplet states of HBO, the proton transfer between the enol and keto tautomers is reversible because the two (enol and keto) triplet states are accidentally isoenergetic. In addition, the rate constant is as slow as milliseconds at 100 K. The results of much slower proton transfer dynamics in the triplet manifold are consistent with the earlier summarization of ESIPT molecules. Based on the steady-state absorption and emission spectroscopy, the changes of pKa between the ground and excited states, and hence the thermodynamics of ESIPT, can be deduced by a Forster cycle [65]. Accordingly, compared to the pKa in the ground state, the decrease of pKa in the... 

Replacing the nitrile group by a benzothiazole produces an important subclass of fluorescent compounds represented by thioflavin T (25, Fig. 10). It is not clear if this compound undergoes deactivation via intramolecular rotation that would meet the criterion for a molecular rotor. The steady-state absorption and emission properties of thioflavin T has been attributed to micelle formation [53, 54], dimer and excimer formation [55, 56], and deactivation through intramolecular rotation [57]. 

Our experimental set-up (described in ref. 7), allows us to record steady state absorption and emission spectra over a wide range of densities (10 5 to 20 at/nm3) in the Ar supercritical domain (Tc = 150.8 K, Pc = 49 bar). Representative absorption and emission spectra are shown in figure 1. These spectra could be reproduced with a good accuracy by means of equilibrium MD simulations performed with a standard procedure [8], In these simulations, the NO X-Ar and Ar-Ar interaction potentials were taken from the literature [9], We extracted an analytical NO A-Ar pair potential by an iterative fit of the experimental spectra, valid for the whole supercritical domain. 

The steady state absorption and emission spectra of poly(A), poly(dA), and the absorption spectrum of the ribonucleotide monomer adenosine 5 -monophosphate (AMP) are shown in Fig. 1. The absorption spectra of poly(A) and poly(dA) are essentially identical. The AMP absorption spectrum is similar to the polymer spectra, but subtle differences exist. The absorption maximum of both homopolymers is shifted to the blue by several hundred wavenumbers, while the low energy band edge is red-shifted with respect to AMP. Similar shifts are observed at 77 K [15]. 

More recently, a RuPc bearing a carboxylic moiety in its axial position was also tested for DSSC applications [281]. Transient absorption and steady-state (absorption and emission) measurements revealed that for such a system the electron injection occurs from the RuPc triplet state into the Ti02 conduction band. A detailed study on the variation of the recombination rate constants for a series of metal complexes and organic dyes, including some RuPcs, has been carried out in order to identify some important parameters that should be taken into account for the implementation of DSSCs [282],... 

By far the largest number of Ceo-based donor-acceptor systems studied to date utilize porphyrins as antennas for efficient light capture in the visible region of the spectrum [306, 308-310, 324, 329, 341], In the following section systems are presented for which time-resolved and steady-state absorption and emission measurements are available, which document the intramolecular electron transfer processes under a variety of experimental conditions. But we also like to acknowledge the purely synthetic work, for which no experimental data is obtainable [342-351]. 

Figure 1.12. Steady state absorption and emission spectra of the first generation...

Fig-l The steady state absorption and emission spectra of (a) methyl ladder type polymer, MeLPPP (b) poly[9,9-di-n-(2 ethylhexyl)fluorene] (PF2/6, n 60) (c), pentafluorene (d) trifluorene and (e) monofluorene measured in dilute toluene solution are compared. The insets depict the chemical structures of each. All spectra were measured in dilute MCH solution... 

Measurements. Steady-state absorption and emission spectra were recorded on a Perkin-Elmer 552 UV-visible and an MPF-44B fluorescence spectrophotometer, respectively. Fluorescence decay rate constants, and quenching rate constants, kgy were measured with a PRA LN-100 nitrogen laser system with fast spectroscopic detection (16, 17). Measurement of the degree of polarization (18-20) and transient absorption via laser photolysis were described in previous studies (21). 

Steady-State Spectral Convolution. The steady state absorption and emission spectra of dilute dye samples can be measured using standard spectroscopic techniques. Once the extinction coefficient, e( ), and the normalized luminescence spectrum, f(v), are known for a particular dye, the self—absorption probability r over a pathlength L in the sample containing the dye at a concentration C is given by... 

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