Dyestuff and Colour Science Introduction. pptx

8/18/2019 Dyestuff and Colour Science Introduction. pptx

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Dyestuf and Color

Science

TET-304

Engr. Nasir Sarwar


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Dye stuf

• Dye:

• An ionized aromatic compound thathave the ability impart color to thesubstrate on which these are applied,is termed as DYE.

• All dyes contains aromaticcompounds.

• Substrate may be textile(iber,!abric, paper, leather, plastics wax,

cosmetic base etc.


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• Aromatic comounds aresubstances that consist o! one ormore rin#s that contain alternatin#

sin#le and double bonds in itschemical structure.

• $enzene


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%ther Examples


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• A dye is a colored substance but ascolored substance are not dye.

• e.#. Azo benzene & 'ed in color butnot Dye hy)


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*roperties o! Dye

• Stable Structure+ Should not #ostructural chan#e easily.

• Should have anity !or its substrate.

• Should be soluble in water or in anysuitable media or made stabledispersion.

• A!ter application should resist tocertain physical-chemical action withacceptable limits.


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hat is color

he perception o! colour is an ability o! someanimals, includin# humans, to detect somewavelen#ths o! electroma#netic radiation

(li#ht/ diferently !rom other wavelen#ths.hen li#ht !all on any ob0ect it absorbs tosome extant and shows re1ectance,transition and scattered.

he potions o! li#ht in visible spectrum o!li#ht reaches to our eye is detected as color


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• 2olor is nothin# 0ust the rays o! certainwave len#th that detected by our eye.

• electrons !all to lower ener#y levels and

#ive of li#ht in the !orm o! a spectrum.• hese spectral lines are actually speci3c

amounts o! ener#y !or when an electron

transitions to a lower ener#y level.• Electrons can only occupy speci3c

ener#y levels in an atom to be stabilized.


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• Electron 0umps and release ener#y in!orm o! rays o! diferent wave len#th.


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• hen an ob0ect absorbs some o! theradiation !rom within that ran#e wesee the waves that are le!t over, and

the ob0ect appears coloured. 4nreality this ran#e we see ma5es uponly a very small !raction o! the

electroma#netic spectrum.


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6uman Eye respond to wavelen#thsbetween about 788+988 nm.


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hat ma5es Dye 2olored

!s !tc"romo"ore###


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• he absorption o! electroma#neticradiation o! varyin# wavelen#ths,dependin# on the ener#y o! the

electron clouds. or this reason,chromophores do not ma5e dyescoloured in the sense that they

con!er on them the ability to absorbradiation.


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• chromophores !unction by alterin#the ener#y in the delocalisedelectron cloud o! the dye, and this

alteration results in the compoundabsorbin# radiation !rom within thevisible ran#e instead o! outside it.

%ur eyes detect that absorption, andrespond to the lac5 o! a completeran#e o! wavelen#ths by seein#

colour.


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Examples o! 2hromophor


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Au$oc"rome


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Au$oc"rome

• he word auxochrome is derived!rom two roots. he pre3x auxo is!rom auxein, and

means increased. he secondpart, chrome means colour, so thebasic meanin# o! the word

auxochrome is colourincreaser. his word was coinedbecause it was noted ori#inally that

the addition o! ionisin# #roups


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Efect o! auxochrome aromatic

system

To the left is naphthalene, a colourless compound.

The addition of a single hydroxyl group to naphthalene

produces 1-naphthol which is also a colourless

compound, but one which can ionise.

If instead of a hydroxyl group we add the nitro

group, which is a chromophore, we get the

compound 2,4-dinitronaphthalene. The addition of

this chromophore has caused it to become pale

yellow.

If instead of a hydroxyl or nitro groups, both a

hydroxyl and nitro groups are added, we get the deep

yellow dye, martius yellow .


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:odi3ers

• ;roups that alter the colour o! dyes byalterin# the ener#y in the delocalizedelectrons.

• hey themselves cannot do this enou#h tocause absorption in the visible ran#e, butthey can afect the shade si#ni3cantlywhen absorption is already in that ran#e.

Addin# more o! a particular modi3er resultsin a pro#ressive alteration o! colour.

• Example + the :ethyl violet series


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:odi3er

%it"out any met"yl grous t"earent dye is calledararosanilin and is red.

%"en 'our met"yl grous areadded we get t"e reddis" urle

dye met"yl (iolet.

As more met"yl grous areadded we get t"e urle )luedye crystal (iolet w"ic" "as si$

suc" grous.

!' a se(ent" met"yl grou isadded* t"e resulting dye ismet"ylgreen.


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erms associated with Dyes

+ue: he de#ree o! stimuli o!absorbin# speci3c wavelen#th.

or understandin#, any o! basic thesebasic color is 6ue

T"ese are t"e 'amily o' twel(eurest colors.• hree *rimary 2olors (';$/• hree Secondary 2olors(=/• Six ertiary 2olors(=/


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Strengt": Absorbance o! Dye at aparticular avelen#th.

A dye with batter stren#th havedeeper shade> at low concentration.

,at"oc"romic S"i't

A structural chan#e which causes the absorptionband to lon#er wavelen#ths (i.e. yellow +?oran#e +? red, violet +? blue +? #reen/ is calleda bathochromic shi!t.


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he reverse shi!t, towards shorter wavelen#ths is5nown as a hypsochromic efect.

• Chromophors- Electron withdrawing groups

• Auxochrome- Electron donating groups A bathochromic shi!t may be caused byincreasin# the electron+withdrawin# power o! the

chromophore (@ or Y/, increasin# the electron+donatin# power o! the auxochrome (Y or @/ andby increasin# the len#th o! the con0u#ated systemconnectin# the two.


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he position o! the chromophore andauxochrome also has an efect. 4n #eneral,the meta position (:/ has the shortest

wavelen#th, and the para (*/ and ortho (%/absorption wavelen#ths are approximatelyeual, and lon#er than meta.


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;roups+cause more bathochromic

shi!t


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"otoc"romism

"otoc"romism is the reversibletrans!ormation o! a chemical species betweentwo !orms by the absorption o!

electroma#netic radiation, where the two!orms have diferent absorption spectra.

4t is consider a !ault in textile.

4t is due to diferent isomeric position o! stabledye structure.


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2is-rans 4somerisim

he terms BcisC and BtransC are !romatin, in which cis means on thissideF and trans means on the other

side or across.

As with any double bond, the planar+GHG+ bond shows #eometrical

isomerism

rans 2is


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• rans !orm is more stable than cis.

•Stron# polar #roup, less will bephotochromism

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Dyestuff and Colour Science Introduction. pptx