An inexpensive flash photolysis apparatus and demonstration experiment

The solvent influence on the absorption spectra and the kinetics of the back reaction of the 1′,3′-dihydro-1′,3′,3′-trimethyl-6-nitrospiro(2H-1-benzopyran-2,2′-2H-indole) (6-NO2-BIPS) has been investigated by means of temperature-controlled, UV–visible spectroscopic measurements. The back reaction process was proved to follow first-order kinetics for five different solvents (toluene, THF, acetonitrile, DMSO, and ethanol) at several temperatures. Kinetics parameters (E a, A, τ, ΔH #, ΔS #, and ΔG #) were extracted from absorbance decay profiles for all solvents, and a simple model based on solvation mechanism was proposed in good agreement with experimental results. Such a photochromic compound also exhibits strong solvatochromism in its merocyanine form. All these experiments were performed to illustrate solvent effects on kinetic processes and optical properties for students with an undergraduate physical chemistry theoretical background. All the experiments described could be performed in a physical chemistry undergraduate laboratory.

Section: Introductionmentioning

confidence: 93%

Influence of the Solvent on the Thermal Back Reaction of One Spiropyran

Piard

2014

“…The Theory interface presents a scrollable window in which the basics of the technique are explained along with the educational literature associated with the topic. − The major functional elements common to nearly all flash photolysis experimental apparatuses are systematically discussed: flash tubes and excitation sources; monitoring beam sources such as xenon, deuterium, and halogen lamps; monochromators; sample cells; photomultiplier tubes; and analog-to-digital converters.…”

Section: Simulation Softwarementioning

confidence: 99%

“…The functional elements of a flash photolysis apparatus are shown on the FlashPhotol interface (see Figure ). The simulator has been modeled along the lines of various apparatuses described in the educational literature that have been designed specifically to illustrate to students the principles of flash photolysis. − In general, such apparatuses are usually constructed from simple components that are readily available. For example, a common photographic flash unit can be utilized as a polychromatic excitation source to produce the transient species.…”

Section: Simulation Softwarementioning

confidence: 99%

FlashPhotol: Using a Flash Photolysis Apparatus Simulator To Introduce Students to the Kinetics of Transient Species and Fast Reactions

Bigger

2016

FlashPhotol is an educational software package that introduces students to the kinetics of transient species and fast reactions. This is achieved by means of a computer-simulated flash photolysis apparatus that comprises all major functional elements and that students can use to perform various experiments. The experimental interface presents a visual representation of the monitoring light beam transmission through the sample cell as well as the corresponding transient concentration after excitation thereby enabling students to fully appreciate the fundamental processes on which the technique relies. Experiments in the package also reinforce students’ understanding of the Beer–Lambert law and illustrate how an absorbance value is produced from internal signals within an instrument. The software includes: (i) a fully contained tutorial on the technique of flash photolysis; and (ii) a procedure for each of the experiments that can be performed using the simulator along with an example results analysis in each case. It is anticipated that instructors may wish to use the simulator for lecture demonstrations, especially in demonstrating the transient process occurring in the sample cell following flash irradiation.

“…In this paper, an experiment is presented in which students excite the azobenzene derivative o -methyl red with a laser pointer and monitor the spectral dynamics using a UV–vis spectrometer with a CCD array detector. Flash photolysis experiments have been proposed for use in teaching laboratories before, − but this experiment takes advantage of the slow isomerization reaction rate of o -methyl red in basic solutions and the ability of a spectrometer with a silicon CCD array detector to quickly collect spectra to examine the spectrum as a function of time. , Azobenzene derivatives are ideal for introducing kinetics concepts to undergraduate physical chemistry students because the rate to re-form the trans conformer from the photoexcited cis conformer is very molecule, solvent, and temperature dependent. ,− In this experiment, students observe how transient spectra change when the solvent is used as a reference and when the solution is used as a reference. Transient absorption dynamics, transient bleach dynamics, and an isosbestic point are observed.…”

Section: Introductionmentioning

confidence: 99%

Flash Photolysis Experiment of o-Methyl Red as a Function of pH: A Low-Cost Experiment for the Undergraduate Physical Chemistry Lab

Larsen

Perkins

2016

A low-cost, time-resolved spectroscopy experiment appropriate for third year physical chemistry students is presented. Students excite o-methyl red in basic solutions with a laser pointer and use a modular spectrometer with a CCD array detector to monitor the transient spectra as the higher-energy cis conformer of the molecule converts back to the thermodynamically more stable trans form. The transient absorption dynamics are monitored as a function of time averaged between 340 and 360 nm, and the transient bleach dynamics are monitored as a function of time averaged between 440 and 460 nm. The bleach dynamics are monitored in basic solutions at several values of pH, and the observed rate constants are used to extract the rate constant for the isomerization of the protonated form and the deprotonated form of the molecule.