Recent advances in photoacoustic calorimetry: Theoretical basis and improvements in experimental design

Abstract

Recent developments in time-resolved photoacoustic calorimetry (PAC) are discussed. An equation is derived relating the amplitude of the maximum photoacoustic signal to parameters of a photoacoustic cell, to physical properties of the solvents, and to the energy deposited as heat. The equation is validated by a series of scaling experiments: it correctly correlates the dependence of the PAC signal on cell thickness, on energy deposition, and on solvent properties. The dominant sources of background signal have been determined and the background signal reduced substantially relative to previous work. It is now possible to measure energies and lifetimes of transients in solutions with optical densities as low as ∼5×10−4. Data are presented for the energy of 2-cyclopentenone triplet, a transient for which interpretable PAC measurements were previously not possible. Its triplet energy is 73.1±1.1 kcal/mole. With reduced background and a faster digital storage oscilloscope, a quite short transient lifetime, 7.53±0.2 ns, and a triplet energy of 51.0±2.1 kcal/mol have been measured for 1,1-bis-(p-bromophenyl)ethene. The lifetime agrees very well with that determined by kinetic absorption spectroscopy and the triplet energy agrees with expectation based on the unsubstituted 1,1-diphenylethene.

(More) About biphenyl first excited triplet state energy

“…We use a front-face irradiation photoacoustic cell [20,22]. In short, the sample, reference and solvent solutions were flown separately with a 0.9 mL/min rate (SSI chromatographic pump) through a 0.22 mm thick cell.…”

“…This is the behaviour expected from reduction of the xanthone lifetime to 3 ns and from the 97% energy transfer from the xanthone triplet to the biphenyl triplet that does not decay within the time resolution of our experiment. The reference and sample photoacoustic waves were deconvoluted using an implementation of the Marquardt algorithm [20], using the kinetic model described above. All waves were interpreted in terms of two sequential decays, each one described by the fraction of thermal heat deposited, φ, within the lifetime τ.…”

“…PAC has proven to be a very useful technique to measure the thermochemistry and kinetics of short lived transients in solution [19,20]. This technique detects the heat released as the excited state reached by photoexcitation decays to lower energy states, including the triplet state.…”

Singlet oxygen quantum yields from halogenated chlorins: potential new photodynamic therapy agents

“…Time-resolved PAC measurements were performed in a homemade apparatus following the front-face irradiation design described by Arnaut et al [20] and discussed in detail elsewhere [1,21,22]. Briefly, we use a PTI N 2 laser (model PL2300) working at a frequency of 2 Hz to pump a PTI dye laser (model PL202) and irradiate the solutions flown through a 0.11 mm photoacoustic cell.…”

Enthalpy, Entropy, and Volume Changes of Electron Transfer Reactions in Photosynthetic Proteins

“…A 28 μm film and 1-mm path cell are used for the nanosecond measurements. A 5-cm dielectric mirror was used according to the design of Arnaut et al (Arnaut et al, 1992). The advantage of using the mirror in the photoacoustic system is two-fold: (1) to increase light absorption and (2) to generate the time delay to eliminate the electric artifact in photoacoustic measurements.…”