Ultrafast Systems KRONOS User manual

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Table of Contents
Table of Contents ........................................................................................................2
Table of Figures ..........................................................................................................4
1. Preface .................................................................................................................5
2. General Safety .......................................................................................................6
2.1 Hazards ...................................................................................................................6
2.2 Electrical Safety .......................................................................................................6
3. Product Specifications ...........................................................................................7
4. Unpacking and Inspection ......................................................................................9
5. Hardware ............................................................................................................10
6. Software .............................................................................................................12
7. Using Kronos .......................................................................................................15
7.1 Setting Up Kronos ...................................................................................................15
7.2 Preparing Kronos for Experiments ...........................................................................15
7.3 Choosing the Excitation and Detection Wavelengths ................................................15
7.4 Acquiring Data .......................................................................................................18
8. Familiarizing Yourself with the Reference Samples ................................................20
8.1 Base Catalysis of the cis-trans Isomerization of Congo Red .....................................20
8.2 Determination of the Activation Energy of the Thermal Back Reaction of One
Spiropyran in Toluene .............................................................................................23
9. Operation of Kronos .............................................................................................27
9.1 Start-Up .................................................................................................................27
9.2 Choose Experiment Mode and Set Parameters .........................................................27
9.3 Finding the Signal ..................................................................................................27
9.4 Acquiring Data .......................................................................................................27
9.5 Shutdown ..............................................................................................................27
10. Basic Theory .......................................................................................................28
10.1 Transient Optical Spectrometry ..............................................................................28
2

10.2 Photochemistry .....................................................................................................29
10.3 Chemical Kinetics .................................................................................................30
10.3.1 Reaction Rate ........................................................................................................30
10.3.2 Rate Expression and Rate Constant ........................................................................30
10.3.3 Order of Reaction ..................................................................................................30
10.3.4 Experimental Approach ..........................................................................................32
11. Maintenance and Troubleshooting .......................................................................33
11.1 Maintenance .........................................................................................................33
11.2 Troubleshooting ....................................................................................................34
12. Appendix ............................................................................................................35
13. Warranty .............................................................................................................36
Limitation of Warranty ...................................................................................................36
14. Notice ................................................................................................................37
14.1 Confidentiality & Proprietary Rights ........................................................................37
14.1.1 Reservation of Title ...............................................................................................37
14.1.2 Preservation of Secrecy and Confidentiality and Restrictions to Access ...................37
14.2 Service Information ...............................................................................................37
3

Table of Figures
Figure 1: Spectral response of detector. ....................................................................................9
Figure 2: 3D render of Kronos .................................................................................................10
(a) without components inserted .........................................................................................10
(b) fully loaded with a cuvette, excitation, and detection filters ..............................................10
(c) Schematic optical layout of the Kronos ...........................................................................10
Figure 3: Screenshot of the Kronos software. ..........................................................................13
Figure 4: Spectra of Kronos light sources: ...............................................................................16
(a) Xenon flash lamp for the pump .......................................................................................16
(b) LED for the probe. ..........................................................................................................16
Figure 5: Transmission spectrum of ........................................................................................17
(a) dark blue or 350-400 + >700 ...........................................................................................17
(b) light blue or 400-700 colored glass excitation filters ........................................................17
Figure 6: Transmission spectrum of 600 nm detection dielectric interference filter. ...................18
Figure 7: Various reference samples used for different experiments in Kronos. The inset shows
the full curve; note the strong spike due to the flash lamp. .........................................19
Figure 9: Ground state absorption spectrum of Congo Red (trans conf.) in 20% water/ethanol. ..21
Figure 10: Kinetic profile of Congo Red in 20% water in ethanol. ...............................................22
Figure 11: Calculated and fitted ΔA plot. .................................................................................23
Figure 12: Structure and photochromic reaction of 6-NO-BIPS. .................................................24
Figure 13: Ground state absorption spectrum of One Spiropyran in toluene. ..............................24
Figure 14: Transient absorption of Spiropyran in Toluene at 600 nm detection wavelength. ........25
Figure 15: Example decay and exponential fit for 55°C measurement. .......................................26
Figure 16: Actual data example of ln(τ) as a function of 1000/T. ..............................................26
Figure 17: Photophysical and photochemical sequence in light-matter interactions. ..................29
Figure 18: Concentration time profiles of reactant and product. ................................................32
4

1. Preface
This document contains user information for the Kronos flash photolysis spectrometer. Kronos is
conceived to be a simple, user-friendly device for demonstrating to chemistry students the
fundamental principles of Chemical Kinetics. Every process labeled as “chemical” occurs as the
result of chemical bonds being broken or formed, i.e. nuclei change their spatial positions with
respect to each other. Chemical Kinetics is one of the major divisions of Physical Chemistry and is
basically the quantitative study of the rates and mechanisms of chemical reactions. Chemical
change can be induced in a variety of ways; the one employed in Kronos is by absorption of light.
Thus, the instrument serves also as a way of introducing the student to the concepts and practice
of Photochemistry.
Read this Documentation carefully before operating the spectrometer for the first time. Special
attention should be given to Section 2: General Safety.
5

2. General Safety
The Kronos flash photolysis spectrometer is designed and manufactured for kinetic analysis of
chemical specimen by means of ultrafast transient absorption spectrometry. And it is not sold, nor
intended for, nor should ever be used for any other purpose. The product should be used solely in
accordance with the instructions provided.
2.1 Hazards
Take extra caution when operating or servicing this equipment:
•If this equipment is used in a manner not specified in this manual, the protection provided by
this equipment may be impaired.
•Handle the cuvette with care. Check the cuvette for damage or cracks and replace any damaged
ones immediately.
•Use extreme caution in handling the cuvette when it is filled with liquid. Always remove the
cuvette before changing contents. Never fill or refill the cuvette when it is in the sample holder.
•The optimal operation temperature of Kronos is at or near room temperature.
2.2 Electrical Safety
Observe these general warnings when operating or servicing this equipment:
•Read all warnings on the unit and in the operating instructions.
•Kronos uses a large capacitor to charge the Xe flash lamp. Dangerous voltage levels are
expected to persist even after unplugging the unit.
•Do not disassemble or open the spectrometer case. Doing so may damage the excitation light
source and risk electric shock.
•Do not use this equipment in or near water.
•Dry the exterior of the cuvette prior to placing it in the holder. Using a cuvette with a wet exterior
or one that is leaking liquid can result in malfunction, shorting of electrical components or
electric shock.
6

3. Product Specifications
Table 1: Product specifications of Kronos.
General Specifications
Footprint (L x W)
135 mm x 105 mm
Weight
1 kg
UL94
V-0
UL796
Meets requirements
USB cable
28 AWG shielded
Power source
USB connection
Supplied current: 500 mA
Supplied voltage: 5 V
Operating temperature
15 to 40 °C
Operating relative humidity
10 to 70% (non-condensing)
Spectrometer Specifications
Spectral coverage
450 -750 nm
Spectral resolution
Depends on the filter used. Typically, ~10 nm
Temporal resolution
~100 μs
Time window
≥ 15 ms
7

Detector Specifications
Detector type
Silicon PIN
Active area
3.6 x 3.6 mm (13 mm2)
Wavelength range
350 to 1100 nm
Rise time
14 ns
Bias voltage
10 V
8

Figure 1: Spectral response of detector.
Kronos produces a 2-dimensional Time-Current data matrix in a form of an ASCII (.CSV file) which
can be easily processed with free or commercially available spreadsheet or graphing software, e.g.
Microsoft Excel, OriginLab Origin, etc.
4. Unpacking and Inspection
The Kronos spectrometer is carefully packaged at the factory to minimize the possibility of
damage during shipping. Inspect the box for external signs of damage or mishandling. Inspect the
contents for damage. If there is visible damage to the instrument upon receipt, inform the shipping
company and Ultrafast Systems immediately.
9

5. Hardware
The Kronos is shown in Figure 2a and b, highlighting the simple design that makes Kronos very
easy to use. Holes are machined into the housing which allows rapid replacements of standard
square filters and cuvettes. The detection filters are mounted in a customized holder. Figure 2c
shows the simplified optical layout of the Kronos.
Figure 2: 3D render of Kronos
(a) without components inserted
(b) fully loaded with a cuvette, excitation, and detection filters
(c) Schematic optical layout of the Kronos
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Table 2: Kronos optical components.
Table 3: Excitation colored glass filters included with the Kronos.
Table 4: Detection dielectric interference filters included with the Kronos with center wavelengths listed.
KRONOS
LED:
LED probe source
Xe lamp:
Xe flash lamp pump source
Sample:
10mm × 10mm cuvette holder
L1, L2:
Lenses
PD:
Silicon photodiode
Exc. filter:
Holder for 25mm × 25mm × 2mm filters (for excitation wavelength selectivity)
Det. filter:
Holder for 0.5”- diameter filters (for detection wavelength selectivity)
Excitation colored glass filters transmitted wavelengths (nm):
300-450 + >700
400-700
Detection dielectric interference filters, 10 nm bandwidth, center lines at (nm):
450
480
500
520
540
560
580
600
620
640
660
680
700
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6. Software
Table 5: UI elements in the Kronos software.
ELEMENT
DESCRIPTION
Amount of probe light reaching the photodiode (Probe intensity, y-axis)
Range
Related to detector gain and LED intensity
Absorption mode: Leave it on Auto
Emission mode: Adjust the range slider to achieve sufficient signal-to-noise
Absorption/Emission
Select either Absorption or Emission experiment modes
Run
Starts measurement
Save
Save data in CSV format
first column: time, in units of seconds
second column: light intensity, in units of amperes
Exit
Exit the program
Average
Number of scans to average across
Time window
Time scan range (x-axis). Use smaller time windows for faster processes.
Photodiode I
0
12

Figure 3: Screenshot of the Kronos software.
Figure 3 shows the Kronos UI. By default, the software will adjust the axis scales automatically: the
Y-axis range will adjust to display the signal only, showing the large spike around time = 0. The
default X-axis setting is “Auto Scale”. To change this, right click anywhere on the plot and choose
the desired option. Alternatively, you can use the graph controls on the top right of the screen, just
above the graph display.
13

Table 6: Graph controls in Kronos.
Table 6 shows the graph controls on the top of the screen allow you to zoom in the graph after
measurements have been completed. By default, cursor mode on the graph is y-axis zoom.
ELEMENT
DESCRIPTION
Axis Autoscale mode OFF and ON
Autoscale axis once
Pan graph
Select between graph zoom modes:
Select X and Y region to zoom in
Select X region to zoom in, keep Y limits unchanged
Select Y region to zoom in, keep X limits unchanged (default)
Autoscale both X and Y axes once to fit graph
Zoom out and in
14

7. Using Kronos
7.1 Setting Up Kronos
The Kronos is initialized by follow the steps below:
1. Connect Kronos to the PC via a USB cable.
2. Wait until Windows recognizes the new USB device.
3. Start the Kronos software. Refer to the Appendix if Kronos does not initialize the correct COM
port.
7.2 Preparing Kronos for Experiments
Before performing any experiments, look for a white glow in the Kronos interior. This means Kronos
is powered up. Remove any samples and allow the LED probe light to be incident on the photodiode
and check that the photodiode meter displays a value. This will be I0, i.e., the baseline intensity
before any pump-induced changes.
In absorption mode during data acquisition, the Kronos will wait for approximately 2 sec between
flashes to allow enough time for the flash capacitors to recharge.
7.3 Choosing the Excitation and Detection Wavelengths
Kronos uses a Xe lamp and LED for the pump and probe light, respectively. Both are broadband
light sources and their spectra is shown in Figure 4. By using an appropriate filter, one of the
square colored glass filters, you can select which wavelength to pump (excite) the sample with,
and what range of wavelengths is measured by the detector. The filters isolate the wavelength of
interest by transmitting said wavelengths and blocking the others.
15

Figure 4: Spectra of Kronos light sources:
(a) Xenon flash lamp for the pump
(b) LED for the probe.
16

Figure 5 shows the transmission spectra of the two colored glass filters included with Kronos. Any
incident light within the high transmittance regions can pass through the filters easily. For example,
the dark blue filter, 300-450 nm + >700 nm, has high transmittance around 350 nm and allows the
Xe lamp to function as a UV/blue light source. If you wish to pump with a separate wavelength
region (e.g. 500 nm), simply use the lighter blue filter, 400-700 nm, which is transparent in that
region.
Figure 5: Transmission spectrum of
(a) dark blue or 350-400 + >700
(b) light blue or 400-700 colored glass excitation filters
17

The detection wavelength range is manually selected by using a 0.5” bandpass filter. The labeled
broad rectangular slit on top of the Kronos housing accommodates one such filter mount. Figure 6
shows the transmission spectrum of the 600 nm bandpass filter included with Kronos. These filters
have a bandwidth, or full width at half maximum of 10 nm (in this scenario, 595 nm to 605 nm). Any
incident light within this bandwidth has high transmittance.
Figure 6: Transmission spectrum of 600 nm detection dielectric interference filter.
7.4 Acquiring Data
Place a filled cuvette into the sample area and select the appropriate parameters for averaging and
time window. For absorption measurements, click on the Absorption radio button. Ensure the
Range is set to auto and do not disable this for absorption measurements. The software will
automatically adjust the detector gain and LED intensity. In absorption mode, both LED and Xe light
sources will be activated.
18

For emission measurements, click on the Emission radio button. Make sure the Range is not set to
Auto, i.e., the check box should be empty. In this mode, only the Xe source will be activated. Trial
and error are required to select the appropriate Range using the slider to obtain good signal-to-
noise.
Click on the <Run> button and allow the measurement to complete. You may notice a large spike
(an artifact) in the first 50 μs present in the absorption kinetics. This is mainly due to
electromagnetic interference in the circuitry and is intrinsic to the equipment. Since the temporal
resolution of the Kronos is around 100 μs, you can safely reject the artifact and simply use the
datapoints after the artifact.
Click on the <Save> button to save the data as a CSV file that can be processed in graphing or
spreadsheet software. The file contains two columns: the first column is the time data, in units of
milliseconds; the second column is the probe intensity data, in units of current (amperes). A
sample graph is shown in Figure 7.
Figure 7: Various reference samples used for different experiments in Kronos. The inset shows the full curve; note the
strong spike due to the flash lamp.
19