27.10.04 ws 04/05-functional π-systems: part 1 1

ω Introduction: From colorants to functional dyes and beyondω Light, color, perception, absorption, reflection (transmission)ω Colorants, dyes, pigments – classification of dyes and pigmentsω Absorption, emission, spectra, excited statesω Structure-color relationshipω Natural dyesω Dye-based processes: Electron transfer, energy transferω Molecular electronicsω Photoinduced charge separation and thermally induced charge

recombination

WS 2004/2005: Functional π- systems, color anddyes: Overview and Topics (part I)

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» H. R. Christen, F. Vögtle, Organische Chemie - Von den Grundlagen zurForschung, Vol. II, Vol. III, Otto Salle Verlag, Frankfurt am Main.

» E. Breitmaier, G. Jung, Organische Chemie: Grundlagen, Stoffklassen,Reaktionen, Konzepte, Molekülstruktur, 4th ed., Thieme, Stuttgart.

» H. Zollinger Colour Chemistry -Syntheses, Properties and Applications ofOrganic Dyes and Pigments, VCH, Weinheim.

» N. J. Turro, ‘Modern Molecular Photochemistry’, The Benjamin/CummingsPublishing Co., Menlo Park.

» M. Klessinger and J. Michl, ‘Excited States and Photochemistry of OrganicMolecules’, VCH, Weinheim.

» F. Vögtle, J. F. Stoddart, M. Shibasaki, Stimulating Concepts inChemistry, Wiley-VCH, Weinheim.

Books and articles

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Visible light and color

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» M. Kollmannsberger, PhD thesis, Universität Regensburg,1999.

tmf

ε

0

8•104

λ (nm)500300

fluorescenceabsorption

B

NN

FF

high quantum yield ofemission

Spectral properties of dyes

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R

CNCNH

SSR R

R = Phλmax = 350 nm

Photochromism: Dihydroaryl principle

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NC

CN

H

CNCN

light

dark

DHA VHF

1

8a

9

10

Dihydroazulene Photochromism

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» Chemie in unserer Zeit1999, 33, 72.

Reaction center of the bacterial photosynthesis(purple bacteria Rhodobacter)

27.10.04 ws 04/05-functional π-systems: part 1 8

» Nature 1998, 395, 583.

Solar cell - dye sensitized device

27.10.04 ws 04/05-functional π-systems: part 1 9

» Nature 1998, 395, 583.

photocurrent actionspectrum

3: dye-sensitizedheterojunction

Solar cell: actionspectrum

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NH-Lysin-Protein+

11

"Retinal + Opsin"Rhodopsin

Solar light – vision – pigment of vision -incandescent bulb

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» J. Griffiths, Chemie in unserer Zeit 1993, 27, 21.

increaseof energy

white light

Dispersion of white light

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N

OHN

NaO3S O2N

dye 2.25

! Perception of the colorsin acidic solution: orangein basic solution: wine red

» H. Zollinger, Color Chemistry.

Structure, color, perception, media effect

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∗ ε, molar absorptivity (molarextinction coefficient) in M-1 cm-1

(1000 cm2mol-1)∗ l, path length of the cell (in cm)∗ c, concentration [in moles per

liter (M)]

clIIE ××== ε0log

Lambert-Beer Law

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Incoming color and reflected color

» H. Beyer, W. Walter, Lehrbuch der Organischen Chemie

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W: neutral (white) pointpc = a/b: purity of the colorC: complementary color pointF: color pointdominant wavelength λD

Taken from Zollinger „ColorChemistry“

CIE chromaticity diagram

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Colorants, dyes, pigments

Colorants (farbige Verbindungen):absorb or emit light in the visible range

(400 – 700 nm)

Dyes (functionalizedcolorants) are soluble(preferentially watersoluble) and colored

materials which can beimmobilized on substrates

Pigments are coloredparticles unsoluble in wateror other solvents in order to

make attachment onsubstrates auxiliary

materials have to be used

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! Subunits of a colorant∗ chromophore∗ auxochromic group (donor group)∗ antiauxochromic group (acceptor group)

! Definition of a chromogen∗ Electron acceptor—chromophore — electron donator

n

acceptordonor

NMe

NMe

+

I-

pushpull

Color-structure relationship

cyanine dye

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! Polyene and polymethine dyes∗ carotinoids∗ cyanine, hemicyanine, streptocyanine, oxonol

! Tri(di)arylmethine dyes∗ malachite green, crystal violet, phthaleins, xanthenes,

(phenolphthalein), azines, methylene blue

! Aza[18]annulenes∗ porphyrines, porphins, corrins, phthalocyanines∗ open-chain tetrapyrrols

Classification of dyes - I

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O

Ethen, λmax(nm) = 180 nm 2,4,6,8-Decatetraen, λmax(nm) = 310 nm

2,4,6,8,10-Dodecapentaen, λmax(nm) = 340 nm

β-Carotin, λmax(nm) = 450 nm, orange

Retinal (Vitamin A-Aldehyd), λmax(nm) = 360 nm

Polyenes

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N NH

NNH

N NH

NNH

N

N N

N

H

A B

CD

A B

CD

A B

CD

porphyrin chlorin corrin

Aza[18]annulenes: Porphyrin, chlorin, corrin

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Aza[18]annulenes: (Metal)Phthalocyanines

N N

NNM

M: metal ion, Cu2+, Ni2+, etc.

absorption spectra:Q band: 650-730 nmB band: 320-340 nm

broken line (---): Ni-phthalocyanine

taken from Zollinger, Color Chemistry

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! Azo dyes and pigments∗ methyl orange, and others

! Carbonyl dyes and pigments∗ indigo, anthraquinone dyes, quinacridones, alizarine,

diketo-pyrrolo-pyrrole and others

Classification of dyes - II

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Azo dyes for reactive dyeing of cellulosic fibers

N N

N

N

N

N

NN

NHNH

N

SO3H

O

HO3S SO3HCl

HO3S SO3H

O H

HO3S

Cl

H

N

C.I. Reactive Red 120

C.I.: color index)

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Diketo-pyrrolo-pyrrole (DPP) dyes

NH NH

O

O

pentalene

3,6 Diphenyl-2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione

• red, high-melting pigment• applications: automotive

paints, coloring of plastics,printing ink

• molecular electronicssolid line: in DMSOdotted line: in the solid state

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• intensity of an allowed transition:εmax ~ 104 – 105

• energy of excitation:(Ea)/kcal mol-1 = 28 600/λ (nm)

• life time of the excited state:ke° ≡ 1/τo ∼ 104 εmax (sec-1) (onlyradiative processes considered)

400 nm 700 nm

"NIR Farbstoffe""UV-Farbstoffe"

Wellenlänge

Absorption band and excited state properties

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! approximate rates ofground state and excitedstate processeslight absorption: 1015 s-1

vibrational relaxation: >1012 s-1

fluorescence: 106 to 109 s-1

intersystem crossing: 10-1 to 105

s-1

phosphorescence: 10-2 to 104 s-1

Jablonski diagram

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Radiative lifetime: τ0 ≈ 10-4/εmax

a weak absorption corresponds to alonger lifetime of the excited state

» J. Chem. Ed. 1998, 75, 615.

∗ S0 → S1 ~340 nm (weakband)

∗ S0 → S2 ≈ 335 nm (intenseband)

∗ lifetime of the excited state(S1): 382 ns

Absorption spectrum of atypical π-system: Pyrene

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Properties of the excited state∗ Excimer formation at higher

concentration∗ fluorescence of the S1 state

(excited monomer) is structuredunlike the excimer emission

∗ other relaxation processes fromS1: S1 → T1 (efficiency about 38 %in ethanol)

Pyrene emission spectra as afunction of concentration (inhexane)

Supramolecular chemistry of the excited stateof pyrene: Monomer and excimer emission

monomer

excimer

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Pyrene: Energy surfaces of the ground stateand excited state

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FDY/LU

FDY/LU

! B. Valeur, Molecular Fluorescence, Wiley-VCH,Weinheim, 2002.

! B. M. Krasovitskii, B. M. Bolotin, Organic LuminescentMaterials, VCH, Weinheim, 1988.

Luminescence and luminescent materials

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FDY/LU

OHO

CO2

OHO

CO2

O

M+M+

fluoresceinfluorescent

phenolphtaleinnon-fluorescent

Fluorescent and non-fluorescent dyes - I

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FDY/LU

N N

H

H

Ph Ph

H

HPhPh

1,4-diphenylbutadienefluorescent

dibenzalazinenon-fluorescent

N+

NB

FF

N NH

-

boradiazaindacenefluorescent

dipyrromethenenon-fluorescent

O

NNPhPh

2,5-diphenyl-1,3,4-oxadiazolefluorescent

Fluorescent and non-fluorescent dyes - II

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ON O

RX

N

O

OH2N

H NH

-O3S

CH3

O

CO2HBr

OHBr

Br

BrO

O

N

CH3

CNNC

CH3

CH3

Eosin Y DCM

C480: R=CH3, X=HC343: R=H, X=COO-C153: R=CF3, X=H

4AP TNS

∗ Dipole moment nearlyzero in the groundstate

∗ Dipol moment is largein the excited state

∗ time dependentfluorescent Stokesshift (TDFSS)

! Acc. Chem. Res. 2003, 36, 95. FDY/LU

Fluorescent dyes: Solvation Dynamics and ProtonTransfer in Supramolecular Assemblies

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O

O

NH

H O

O

N CH3H

N MeMe

NMe2Me2N

N

S NMe2Me2N

2-aminoanthraquinone (A) 1-methylamino-anthraquinone (B)

+Cl-

crystal violet (C)

+

methylene blue (D)

Structure-color relationship - I

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Structure-color relationship - II

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NN

H

H

(E)-Azobenzene (E)-Stilbene

N

H

N

MeMe

Benzylideneaniline

Indolenine

(twisted around C-N)

(planar; λmax = 310/235 nm)

» taken from Zollinger„Color Chemistry“

Structure-color relationship III:Similarity of absorption spectra of different chromophores

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Structure-color relationship IV: Pigments absorbing inthe visible region of the spectrum

» Pure Appl. Chem. 1996, 68, 1373.

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! Pure Appl. Chem. 1996, 68, 1373.

Structure-color relationship V: Spectral parameters

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∗ Chlorophylls have two absorption bands, one in the red one in the blue∗ Phycoerythrins absorb blue and green light∗ Phycocyanins absorb yellow light

» D. Voet, J.G. Voet,Biochemistry, Wiley,New York,1995

Natural dyes - I: Photosynthesis

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O

OH

OH

OH

OHR

R

aglycon (anthocyanidin);sugars are bound at O-3 and O-5

35

7

4'+

! F. Pina, M. J. Melo, MT. Goto, T. Kondo, Angew. Chem. 1991, 103, 17.

∗ widely distributed throughthe plant kingdom

∗ colours reaching fromsalmon, pink, scarlet,magenta, violet to blue.

∗ molecular stackingphenomena, hydrogenbonding

! flavonoids and anthocyanins

O

O

O

flavon flavylium cation

+

Natural dyes II: flowers

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kET

» M. N. Paddon-Row. Electron and Energy Transfer. In Stimulating Concepts inChemistry; Vögtle, F.; Stoddart, J. F.; Shibasaki, M. Eds.; Wiley-VCH,Weinheim, 2000; pp. 267-291.

kET ∼ e-ßr

r: distancebetween D and Aß: damping factor

D-A → D+-A-(charge separation)

λ: reorganization energy

Basic processes of dyes:electron transfer (ET)

donor-bridge-acceptor

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» R. A. Marcus, Angew. Chem. 1993, 105, 1161-1280.

!normal and inverted region

reaction coordinate

Marcus theory

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2

14

°∆+=∆ ∗

λλ GG

TkG

ETBeAk∗∆

−

⋅=

! R. A. Marcus, Angew.Chem. 1993, 105, 1161-1280.

Electron transfer:normal andinverted region

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» J. R. Miller, L. T. Calcaterra, G. L. Closs, J.Am. Chem. Soc. 1984, 106, 3047-3049.

!puls radiation studies(solvated electrons)

Experimental proof of the Marcus-inverted region

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» M. N. Paddon-Row. Electronand Energy Transfer. InStimulating Concepts inChemistry; Vögtle, F.;Stoddart, J. F.; Shibasaki, M.Eds.; Wiley-VCH: Weinheim,2000; pp. 267-291.

∗ Electronic excitationenergy transfer (EET)

rate ~ 1/r6

rate ~ e-r

Basic processes of energytransfer: Excitation energytransfer (EET)

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» J. M. Tour, inStimulating Concepts inChemistry (Eds.: F.Vögtle, J. F. Stoddart,M. Shibasaki), Wiley-VCH, Weinheim, 2000,pp. 237-253.

∗ Molecular Diodes

Components of molecular electronics

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» J. Am. Chem. Soc. 1996, 118, 6767.

∗ Generation of long lived charge separation in the excited state:quantum yield 0.92, energy storage ~2 eV, life time 300 ns

N NN N N C8H17

O

O

O

O

O

OMeO

Energy conversion (energy storage): Photoinducedcharge separation

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» M. N. Paddon-Row, in StimulatingConcepts in Chemistry, 2000, pp.267.

Photosynthesis and charge separation

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Charge recombination: D+-A- → D-A or [D-A]*

! formationof excitedstate P*

Inverted region: Excited state may be populatedunder highly exothermic condition (ECL)

??