This paper according matter structure theory and physics chemical principle. Elaborate the molecular structure of the common penetrate testing red color dye and fluorescent dye with its chromophoric and luminescence mechanism. Go further to discuss what structure that due to increase the color dye chromophorie intensity and the fluorescent dye luminescence intensity. Then raising penetrate testing liquid sensitivity.
The red color dye and fluorescent dye is the nucleus composition of the penetrate agent. Research the red color dye and fluorescent dye their molecular structure relation with their chromophoric and luminescence principle is the most necessary to the PT science worker. To judge what structure that due to increase the color dye chromophoric intensity and the fluorescent dye luminescence intensity. Then we can raise penetrate testing liquid sensitivity.
Keywords: PT, Dye, Molecular structure, Chromophoric luminescence mechanism
The color dye molecular structure and it chromophoric principle
General the color dye molecular consist of chromophore group、 auxochrome group and aromaticity conjugate structure. General chromophore is azo. quinoid carbonyl、nitroso、nitro-group、carbonyl、vinyl group. (-N=N-, C=O, -NO,-NO2,>C=O, -C=C-) etc unsaturated group. General auxochrome group are Amino、methylamino 、dimethylamino、hydroxy、alkoxyl group （-NH2、-NHCH3、-N(CH3)2,-OH、-OR etc giving electron group),nitro-group (-NO2,absortrion electron group). Aromaticity conjugate structure may be benzene cycle、naphthyl
cycle、 anthracene cycle、perylene cycle、condensed cycle etc. conjugate structure.
According modern quantum organic chemistry molecular orbital theory organic dye chromophoric cause is chrome group unsaturated πbond's electron, or non-bonding electronic pair n electron with aromaticity conjugate system πelectron combine to a bigπ-bond, it can reduce bigπ-bond energy, increaseπor n electron activity. Theseπor n electron can absorb some wavelength visible light photon energy. Transit to the higher energy anti-π-bond orbital, π→π*,n→π*,them reflex some no absorb wavelength visible light. We see it color. These transit photoelectron transfer their energy through molecular thermal motion. jump back to ground state. Example absorb 400-605 nm wavelength reflex 605-700nm red light, general call them as complement color principle.
The chromophoric intensity influence factor:
Several the merchant color dye chromephore intensity compare as follow:
- A. Chromophore group structure influence: Different Chromophoric group structure, they have different giving electron ability, as the Chromophoric group structure giving electron ability is larger, the absorb photon ability is larger, the extinction coefficient is larger, then reflect bright-color. General the azo >quinoid canbonyl>nitroso > carbonyl >vinyl group.
- B. Aromaticity ring structure influence: When aromaticity ring mumber increase, the conjugate double bond increase, conjugate system enlarge. Theπ-bond energy reduce,πor n electron activity increase. Absorb wavelength move toward long wavelength, that yield obvious red shift, absorb photon ability increase, color is brilliant.
- C. Auxochrome group influence: When giving electron auxochrome group such as amino、methylamino、dimethylaminio、hydroxy、alkoxyl group, lead into aromaticity conjugate system one side. The giving electron group contain one pair electron, they join conjugationπ-bond system form p-πconjugate action, increase the conjugation bigπ-bond electron cloud density reduceπorbital energy. Then absorb wave length toward long wavelength and deepen color. When absorb electron group such as nitro-group lead into aromaticity meta position. It can intensitify the bigπ-bond polarization, increase absorb photon intensity and deepen color.
- D. Hetercycle ring influence: When aromaticity conjugate system lead into hetercycle ring, heter-atom in hetercycle can increase conjugate effect then deepen dye color, general the five- membered hetercycle is correspondence a giving electron ring, and the six-membered hetercycle is correspondence a absorb electron ring.
The Fluorescent dye molecular structure and it luminescence principle
Aromaticity fluorescent dye molecular structure is formed by a big rigid plane aromaticity conjugateπ-bond system. When ultraviolet light shine. The conjugate systemπor n electron absorb ultraviolet photon energy jump toπ*anti-bond orbital. π→π*,n→π*,due to molecular rigid these absorb energy no tranfer to molecular thermal motion. Theππ*and nπ*electron fall back ground state and radiate longer wavelength visiable fluorescent light.
The fluorescent intensity influence factror:
- A. conjugateπ-bond system. As the aromaticity conjugateπ-bond system is larger, π-bond energy is lower, fluorescent quantum yield is higher, the fluorescent intensity is stronger, the fluorescent wave peak move toward longer wavelength as follow.
- B. Rigid plane structure: Almost aromaticity fluorescent dye matrix molecular is plane configuration. It posses specified rigid. It can increase the exciation photon-electron radiation transition stability and reduce non -radiation transition chance. So increase fluorescent quantum yield rate. Example fluorene and biphenyl on similar condition. The former fluorescent yield efficiency near 1 and the latter is only 0.2. Their different is former (fluorone) put in methylene. So let fluorene rigid strengthen. At same reason, the azobenzene does not radiate fluorescent and the hetercyclic nitrogen phenanthrene radiate fluorescent.
- C. Substituent influence: as the giving electron substituent such as-NH2、-NHR、-NR2、-OH、-OR、-CN etc、lead to aromaticity ring due to their n electron conjugate with aromaticity ring big π-bond. increase n→π* transit, enlarge conjugate system and so absorb spectrum and emission spectrum wavelength is longer than unsubstituted aromaticity ring and the quantum yield rate is higher, and so reinforce fluorescent. As the absorb electron substituent such as -NO2、-N=N-、-C=O、etc,they can reduce aromaticity ring conjugate system electron cloud density and so reduce fluorescent quantum yield rate. Beside the substituent position can influence fluorescent. General substituted in ortho and para position can enhance fluorescent, while in metra-position can suppression fluorescent.
- D. Hetereycle influence:When hetercycle ring lead to aromaticity ring conjugate system. They can influence fluorescent emission. General the five-membered ring hetercycle performance as a giving electron group enhance fluorescent intensity, and while six-membered ring hetercycle performance as a absorb electron group and reduce fluorescent intensity. Compare as follow.
Imidazo axazole pyrimidine oxazomidime
Several the merchant fluorescent dye luminescene intensity compare as follow:
"The Handbook of Chemical Industry Product. Dye Organic Pigment." Chemical Industry Publishing House 1995
- "Fluorescent Analytical Method," Xiamen University, Chen Kuozhen etc. Science Publishing House 1990.