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In this work, we have investigated the dependence on the pH of the photophysical properties of a functionalized perylene bisimide (PBI) and its potential pH sensing applications. Observed was the presence of aggregates which diminishes at acid pH values and low concentrations, without totally disappearing until a temperature of 80 °C was reached. At basic pH, significant changes in the absorption spectrum were observed, which were associated with more strongly coupled aggregates. The 1H NMR spectra of the PBI dye in D2O/TFA also showed the dependence of aggregation on concentration and temperature. PBI fluorescence intensity and lifetime were also sensitive to pH values. The maximum fluorescence intensity and lifetime were observed in acid medium, in which protonation of the secondary amines on the PBI side chains likely hinders the formation of strongly coupled aggregates. On the contrary, the fluorescence intensity significantly decreased in basic medium, due to deprotonation of the amine groups and the formation of stronger aggregates. Density functional theory calculations corroborated that π-stacked aggregates of PBI derivatives are stable in the protonated state, but their supramolecular structure changes. In the aggregate, monomeric units slide over their adjacent ones and increase the intermolecular distance upon the protonation. Intermolecular hydrogen bonds can help maintain the stability of the protonated aggregate. Fluorescence lifetime showed a sigmoidal dependence on pH, with a linear response range between pH 6 and 8, both in Tris·HCl buffered solutions and in a synthetic buffer mimicking the intracellular environment. The biocompatibility of the PBI dye was tested in C3H10T1/2 mesenchymal cells. The cellular uptake was confirmed by confocal fluorescence microscopy. No significant effects on cellular viability and morphology were observed at the conditions in which compound 1can be used as a fluorescent probe. This work supports the idea that PBI derivatives can be suitable dyes for fluorescence lifetime sensing applications.

We report here the rate coefficients for the OH reactions (kOH) with E-CF3CHCHF and Z-CF3CHCHF, potential substitutes of HFC-134a, as a function of temperature (263–358 K) and pressure (45–300 Torr) by pulsed laser photolysis coupled to laser-induced fluorescence techniques. For the E-isomer, the existing discrepancy among previous results on the Tdependence of kOHneeds to be elucidated. For the Z-isomer, this work constitutes the first absolute determination of kOH. No pressure dependence of kOHwas observed, while kOHexhibits a non-Arrhenius behavior: kOH(E) = (7.6±0.2)×10−13(T298)2.44⁡exp(666±10T)and kOH(Z) = (1.4±0.1)×10−13(T298)1.91⁡exp(640±13T)cm3molecule–1s–1, where uncertainties are 2σ. UV absorption cross sections, σλ, are reported for the first time. From σλand considering a photolysis quantum yield of 1, an upper limit for the photolysis rate coefficients and lifetimes due to this process in the troposphere are estimated: 3 × 10–8s–1and >1 year for the E-isomer and 2 × 10–7s–1and >2 months for Z-CF3CHCHF, respectively. Under these conditions, the overall estimated tropospheric lifetimes are 15 days (for the E-isomer) and 8 days (for the Z-isomer), the major degradation pathway being the OH reaction, with a contribution of the photolytic pathway of less than 3% (for E) and 13% (for Z). IR absorption cross sections were determined both experimentally (500–4000 cm–1) and theoretically (0–2000 cm–1). From the theoretical IR measurements, it is concluded that the contribution of the 0–500 cm–1region to the total integrated cross sections is appreciable for the E-isomer (9%) but almost negligible for the Z-isomer (0.5%). Nevertheless, the impact on their radiative efficiency and global warming potential is negligible.