An introduction to the An introduction to the Pigment Research ProjectPigment Research Project

Light, Color and PigmentsLight, Color and Pigments

Chemistry 123Spring 2008

Dr. Woodward

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)

Ohio REEL ProjectOhio REEL ProjectResearch Experiences to Enhance LearningResearch Experiences to Enhance Learning

http://ohio-reel.osu.edu/

Supported by the National Science Foundation

How does a research module How does a research module differ from a “normal” labdiffer 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 TimelineResearch Timeline

Week ofWeek of Mon/Tue LabMon/Tue Lab Wed/Thur LabWed/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:REEL-I: Use X-ray fluorescence (XRF) and X-ray powder diffraction (XRPD) to identify an unknown salt

REEL-II:REEL-II: Use UV-Visible (UV-Vis) spectroscopy to probe the electronic structures of transition metal complexes in solution

REEL-III: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:REEL-IV: Build on the ideas developed in REEL-III to prepare and characterize inorganic pigments of your own design.

LogisticsLogistics• 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 MentorsPeer 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 MethodsExperimental Methods• Synthesis

– Direct solid state reactions

• Characterization– X-ray powder diffraction– X-ray fluorescence– UV-Visible Spectroscopy

X-ray Powder Diffractometer

(~$65,000)

Ocean Optics UV-Visible Spectrometer (~$7,000)

PigmentsPigments

Pigment: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 ColorCauses of Color• Emitted Light

– Blackbody Radiation, IncandesenceBlackbody Radiation, Incandesence (light bulb, flame)– Gas Discharges/ExcitationsGas Discharges/Excitations (neon lights, aurora borealis)– LuminescenceLuminescence (LED’s, fluoresecent lights,

chemluminescence)

• Steering and/or Interference Effects– Dispersive RefractionDispersive Refraction (rainbows, prisms)– ScatteringScattering (blue sky)– Interference & DiffractionInterference & Diffraction (butterflies, beetles, opals, CD’s)

• Absorbed Light– Intra-atomic excitationsIntra-atomic excitations ((Complex ions, gemstones)– Molecular Orbital ExcitationsMolecular Orbital Excitations ((Chlorophyll, organic dyes)

– Band to Band Transitions in SemiconductorsBand to Band Transitions in Semiconductors (CdS, SnS2, HgS)

– Interatomic (charge transfer) excitationsInteratomic (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 SpectrumThe Electromagnetic Spectrum

Violet

Blue Green

Yellow

Orange

Red

34 86.626 10 2.998 10 /J s m shcE

Properties of Electromagnetic Properties of Electromagnetic Radiation (Light)Radiation (Light)

E h

Quantity Units

Energy, E Joules

Frequency, 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

c

The Color WheelThe Color Wheel

UV 100-400 nm 12.4 - 3.10 eVViolet 400-425 nm 3.10 - 2.92 eVBlue 425-492 nm 2.92 - 2.52 eVGreen 492-575 nm 2.52 - 2.15 eVYellow 575-585 nm 2.15 - 2.12 eVOrange 585-647 nm 2.12 - 1.92 eVRed 647-700 nm 1.92 - 1.77 eVNear IR 10,000-700 nm1.77 - 0.12 eV

1 eV = 1.602 10−19 J

Absorption of Light & ColorAbsorption of Light & ColorIf 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 & ColorAbsorption of Light & ColorIf 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 SpectroscopyUV-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 CuColor and Cu2+2+ complexes complexes

[Cu(H2O)4]2+ [Cu(NH3)4]2+