Porphyrins phosphorescence, quenching

Addition of an inorganic sheet and a PVT-MV + layer results in efficient quenching of the porphyrin phosphorescence at 720 nm, due to electron transfer from excited porphyrin to MV +. Electron-transfer quantum yields were calculated as 0.58 and 0.76 for a-ZrP and HTiNbOs spacers, respectively. Figure 38 shows the steady-state emission spectrum of such a multilayer system. 

The phosphorescence decay kinetics of the triplet excited states of CuP molecules (Fig. 14) is adequately described by Eq. (16). Using this equation one can obtain the values of the parameter p = (Tra /2) In2 veT from the initial non-exponential part of the phosphorescence decay curves and the values of t = l/ k, i.e. the characteristic time of phosphorescence decay, from the final exponential part. Then the data on the dependence of the quantum yield of CuP phosphorescence on the concentration of C(N02)4 have been used to estimate the effective radii of electron tunneling from triplet excited copper porphyrins to C(N02)4 within the time x R, = (ac/2) In vet (Table 3). In doing so, the quenching of CuP luminescence by electron abstraction was assumed to be the only process leading to a decrease in the quantum yield of CuP phosphorescence in the presence of C(N02)4. From Table 3 an electron is seen to tunnel, within the lifetime of triplet excited states x at 10-4s, from CuP particles to C(N02)4 molecules over the distance R, 11 A. Further, the parameter vc and ae for different porphyrins were estimated from the values of (3, Rt, and x. These values are also cited in Table 3. 

The OLED-based sensors were tested in the 23-60°C temperature range. The values of t are expected to generally decrease with increasing temperature, as the PL quenching is enhanced at elevated temperatures [47]. However, in the 23-60°C studied range, the phosphorescence of porphyrins is only slightly dependent on the temperature [68]. Indeed, the temperature effect on the SV plots was minimal small reductions in tq and t (100% O2) were observed as the temperature increased, e.g., for one film, tq decreased from 91 to 84 js with Sg varying from 36.5 to 37.5. 

Long-decay luminescent dyes and probes that are effectively quenched by molecular oxygen can be used for its quantitation. Examples of such probes include ruthe-nium(II)-rm(diphenyl phenanthroline) and phosphorescent platinum(II) porphyrins. Their long emission lifetimes facilitate quantitation by lifetime or intensity measurements. Other chemical specie, such as heavy-metal ions and heterocyclic compounds, can be quantified by luminescence quenching, according to Eq. 3. 

The use of metalloporphyrin-based materials for the detection of molecular oxygen is well developed. One approach that has been employed extensively involves the well-known phenomenon of quenching of metalloporphyrin phosphorescence by O2. Due to their high phosphorescence quantum yields and short triplet lifetimes, platinum and palladium porphyrins were originally suggested as probes... 

---