An introduction to the
Pigment Research Project
Light, Color and Pigments
Chemistry 123
Spring 2008
Dr. Woodward
Ohio REEL Project
Research Experiences to Enhance Learning
Partner Institutions
University of Akron (UA)
Bowling Green State University (BGSU)
Capital University (CU)
Central State University (CtlSU)
University of Cincinnati (UC)
Cleveland State University (CSU)
Columbus State Community College (CSCC)
University of Dayton (UD)
Kent State University (KSU)
Miami University of Ohio (MU)
Ohio University (OU)
University of Toledo (UT)
Wright State University (WSU)
Youngstown State University (YSU)
The Ohio State University (OSU)
http://ohio-reel.osu.edu/
Supported by the National Science Foundation
How does a research module differ
from a “normal” lab
• Research exploration
– Outcome is not known in advance
• Involves all phases of the research process
– Form a hypothesis
– Conduct experiments to test hypothesis
– Interpret & report results
– Modify hypothesis
• Tackles problems of societal interest
– Chemistry plays a central role in many challenges
facing society
• Builds on previous experiments
– The details of the experiment evolve from year to year
Research Timeline
Week of
Mon/Tue Lab
Wed/Thur Lab
April 28
REEL-I,II & III
REEL-I,II & III
May 5
REEL-III & IV
REEL-IV
May 12
REEL-IV
REEL-IV
REEL-I: Use X-ray fluorescence (XRF) and X-ray powder diffraction (XRPD) to
identify an unknown salt
REEL-II: Use UV-Visible (UV-Vis) spectroscopy to probe the electronic structures
of transition metal complexes in solution
REEL-III: Use solid state reactions to prepare pigments, characterize the
composition, crystal structure and electronic structure of the pigments using
XRF, XRPD and UV-Vis methods.
REEL-IV: Build on the ideas developed in REEL-III to prepare and characterize
inorganic pigments of your own design.
Logistics
• Research will be conducted in teams
– Students will work in teams (~4 students per team)
• Research will be pursued collaboratively
– Dr. Woodward & Dr. Stoltzfus
– REEL Lab Coordinator (Harry Seibel)
– Teaching Assistants
– Peer Mentors
• Research presentation
– Each research group will present their results at one of
three REEL poster presentations (May 20,21,22)
• Research documentation and reporting
– Each student will prepare a report in the form of a
scientific paper to describe their research findings
Peer Mentors
Back Row: Lana Alghotani, Sachin Sharma, Jen Scherer, Alex Paraskos, Eric Smith,
Sarah Watson, Ashley Doles, Derek Heimlich, David Albani, Front Row: Jalpa Patel,
Sam Karnitis, Gina Aloisio, Stephen Smith, Brittany Thompson, Ravi Rajmohon, Ken
Verdell, Amy Ullman, Amy Tucker, and Kristen Brandt
Experimental Methods
• Synthesis
– Direct solid state reactions
• Characterization
– X-ray powder diffraction
– X-ray fluorescence
– UV-Visible Spectroscopy
Ocean Optics UV-Visible
Spectrometer (~$7,000)
X-ray Powder Diffractometer
(~$65,000)
Pigments
Pigment: Coloring matter used to make paint.
Pigments work by selectively absorbing a portion of the visible
light while the remaining visible light is reflected.
For more info see
http://webexhibits.org/pigments/
Causes of Color
•
Emitted Light
–
–
–
•
Steering and/or Interference Effects
–
–
–
•
Blackbody Radiation, Incandesence (light bulb, flame)
Gas Discharges/Excitations (neon lights, aurora borealis)
Luminescence (LED’s, fluoresecent lights, chemluminescence)
Dispersive Refraction (rainbows, prisms)
Scattering (blue sky)
Interference & Diffraction (butterflies, beetles, opals, CD’s)
Absorbed Light
–
–
–
–
Intra-atomic excitations (Complex ions, gemstones)
Molecular Orbital Excitations (Chlorophyll, organic dyes)
Band to Band Transitions in Semiconductors (CdS, SnS2, HgS)
Interatomic (charge transfer) excitations
• Oxoanions (i.e. CrO42−, MnO4−), Pigments (Prussian blue,
chrome yellow), gemstones (sapphire)
For more info see http://webexhibits.org/causesofcolor/
The Electromagnetic Spectrum
Violet
Blue
Green
Yellow
Orange
Red
Properties of Electromagnetic Radiation
(Light)
Quantity
c  
Units
Energy, E
Joules
Frequency, n
1/s or Hz
Wavelength, λ
meters
Speed of Light, c
2.998  108 m/s
Planck’s constant, h
6.626  10−34 J∙s
E  h
E
hc




6.626  1034 J  s 2.998  108 m / s


The Color Wheel
UV
Violet
Blue
Green
Yellow
Orange
Red
Near IR
100-400 nm
400-425 nm
425-492 nm
492-575 nm
575-585 nm
585-647 nm
647-700 nm
10,000-700 nm
12.4 - 3.10 eV
3.10 - 2.92 eV
2.92 - 2.52 eV
2.52 - 2.15 eV
2.15 - 2.12 eV
2.12 - 1.92 eV
1.92 - 1.77 eV
1.77 - 0.12 eV
1 eV = 1.602  10−19 J
Absorption of Light & Color
If absorbance occurs in one region of the color wheel the material
appears with the opposite (complimentary color).
– a material absorbs violet light  Color = Yellow
– a material absorbs green light  Color = Red
Absorption of Light & Color
If absorbance occurs in multiple regions of the color wheel the material
generally takes on a color in the middle of the colors that are not
absorbed.
– a material absorbs violet, blue and green light  Color = Orange
– a material absorbs violet and red light  Color = Yellow-Green
UV-Visible Spectroscopy
Monochromatic light (light of a single wavelength) is passed
through the sample and the amount of light absorbed by the
sample is measured.
Color and Cu2+ complexes
[Cu(H2O)4]2+
[Cu(NH3)4]2+