Jablonski diagram and its application in day to day life

This presentation tells about the application of ja jablonski diagram

1. JABLONSKI DIAGRAM PRESENTED BY : JEEBAN ROUT ROLL NO :- CH/31/23 PG DEPARTMENT OF CHEMISTRY FAKIR MOHAN UNIVERSITY , BALASORE

2. CONTENT Introduction Terms Use In Jablonski Diagram Features Of Jablonski Diagram Transition I ) Absorption Of Light Ii ) Emission Of Light Radiative Decay Non Radiative Decay Fluorescence Phosphorescence Quenching Conclusion

3. INTRODUCTION The Jablonski diagram was first proposed by professor Alexander Jablonski in 1935 to describe absorption and emission of light. Jablonski diagram is a common representation of the possible electronic state and transitions as the molecule enters and leaves the excited state. As Jablonski diagram describe the electronic states of molecules , transition and associated light emitting phenomena. The Jablonski diagram represents the energy levels within a molecule where valence electrons can be excited. The Jablonski diagram demonstrates processes such absorption ,fluorescence , phosphorescence.

4. TERMS USED IN JABLONSKI DIAGRAM SPIN MULTIPLICITY i. According to Pauli exclusion principle ,two electrons in an orbital can’t have same quantum number. ii. Molecules have an even number of electrons and thus in ground state,all the electron spins are paired. iii. Spin multiplicity can represent by ( 2S+1 ); where, S is total spin. iv. When electron spins are paired , then upward orientation of the electron spin is cancelled by the downward orientation, so that S=0. s 1 =1/2, s 2 =1/2, total spin S= s 1 +s 2 =1/2+1/2=0 .Hence, 2S+1=1,thus it called as molecule is in singlet ground state . v. When electrons are in parallel spin ,then s 1 =s 2 =1/2, so S=s 1 +s 2 =1/2+1/2=1, 2S+1=3 and the molecule is in triplet state .

5. FEATURES OF JABLONSKI DIAGRAM Energy is on vertical axis. Columns are present on horizontal axis that represents a specific spin multiplicity for a specific specie. The thicker line explain the Electronic energy level and also called singlet and triplet state. Singlet ground state (S ) and excited singlet state (S 1 ,S 2 ,S 3 ) . The thinner lines denote Vibrational energy state. As Electronic energy states increases , the difference between energy become less.

6. FEATURES OF JABLONSKI DIAGRAM

7. TRANSITIONS When a molecule absorbs a photon , the photon energy is converted and increases the molecule’s internal energy level. Likewise, when an excited molecule releases energy, it can do so in the form of a photon. Depending on the energy of the photon , this could correspond to a change in vibrational, electronic, rotational energy level. The changes in these levels are called “ transition ” Two types of transitions are important that is , I )Absorption II) Emission

8. ABSORPTION OF LIGHT The process by which photon , the fundamental unit of light, are absorbed by atom , molecule. When photon collides with an atom or molecule, it can transfer its energy to the particles causing electronic transition or vibration within the material. Electrons orbiting the nucleus of an atom exist in discrete energy levels or orbitals. When a photon with an energy level matching the energy difference between electron orbitals strikes an atom or molecule , it can excite an electron to a higher energy level.

9. ABSORPTION OF LIGHT The beer-lambert law is commonly applied to chemical analysis measurement the concentration of chemical species that absorb light. Mathematical expression for determination of absorbance , log 10 ( i / i ) = a = A is the absorbance. molar absorption co-efficient. Is the optical path length. C is concentration. Absorbance is very fast transitions, on the order 10 -15 .  

10. EMISSION OF LIGHT Excited state are shot lived. The molecule exists for nano seconds in this excited state . Process of relaxation of excited electrons is known as emission. Relaxation of the electrons of excited state can take place by number of methods; Radiative decay Non radiative decay

11. NON RADIATIVE TRANSITION The process in which an electron or an atom undergoes a change in its energy state without emitting a photon. In other words, in this process the absorbed energy is released in the form of heat or any other medium except the radiation. The process are following types ; 1.Internal conversion 2.Intersystem crossing

12. Vibrational Relaxation and Internal Conversion Migration of electrons from higher energy state to lower energy state by the loss of absorbed energy is called relaxation. It is indicated as curved arrows between vibrational levels. If relaxation occurs between vibrational levels in same electronic state, then this phenomenon is called vibrational relaxation . This process is also very fast and takes place between 10 -14 to 10 -11. If the vibrational energy levels are strongly overlapped to electronic energy levels then internal conversion takes place. This overlap of vibrational energy levels to electronic energy levels is due to increase in energies, as energy increases they came nearer to each other.

13. Vibrational Relaxation and Internal Conversion The transition from higher excited state ( S 3 , S 2 or T 3 ,T 2 ) to the first excited state ( S 1 or T 1 ) is called internal conversion. The molecule spin state of internal conversion remain same .Where as it changes in intersystem crossing. The excitation energy is transferred into heat. S 2 S 1 + heat T 2 T 1 +heat

14. Intersystem Crossing Intersystem crossing is an isoenergetic radiationless process involving a transition between the two electronic state with different spin multiplicity. It is slower than internal conversion. It is more likely in a molecule having a heavy nuclei. It emits energy in the form of heat. ISC represents as ; S 1 T 1 + heat S 2 T 2 +heat

15. RADIATIVE TRANSITION The relaxation or de-excitation process which is accompanied with the emission of radiation is called radiative transition. The emitted radiation has lesser energy as compare to absorbed radiation. Because the molecular collision consume some of the energy after absorption. The radiative decay is following types; 1. Fluorescence 2.Phosphorescence

16. JABLONSKI ENERGY DIAGRAM

17. FLUORESCENCE When the incident light falls on a certain substance , they emits visible radiation of different frequency and stops as soon as the light is cut off , this phenomenon is known as fluorescence and the substance are called as fluorescent substances. S h S 1 radiative S + h Example : fluorite, calcite ,gypsum ,talc ,amber etc.. The time period of fluorescence is about 10 -8 . It is the form of luminescence. The energy of the photon emitted in fluorescence is the same energy as the difference between the eigenstates of the transition , the energy of fluorescence photon is lesser than energy of excited photon. The difference is because energy is lost in internal conversion &vibrational relaxation.  

18. TYPES OF FLUORESCENCE Stokes fluorescence: The wavelength of emitted radiation is longer than that of the absorbed radiation. Anti Stokes Fluorescence: The wavelength of emitted radiation is shorter than the absorbed radiation. Resonance Fluorescence: when the wavelength of emitted radiation is equal to absorbed radiation . Prompt Fluorescence: The release of electromagnetic energy is immediate or from the singlet state.

19. FACTORS AFFECTING FLUORESCENCE Conjugation: A molecule should posses conjugation(pi-electron) so that the Visible & UV radiation could absorbed. Nature of Substituent Groups: EDG can enhance fluorescence e.g. –OH , -NH 2 .EWG decrease fluorescence e.g. –COOH , NO 2 . Concentration: Fluorescence intensity is directly proportional to concentration. Viscosity: Increased viscosity, decreases the chance of collision of molecules thereby decreasing fluorescence. Rigidity: More rigid the structure of molecule , more the intensity of fluorescence. Atomic number: Atoms of higher atomic number , decreases the chance of fluorescence & increases the chance of Phosphorescence.

20. APPLICATION OF FLUORESCENCE Fluorescence spectroscopy can be used to study the structure and dynamics of proteins , membranes and also detect intracellular ion concentrations . It can used to distinguish between citrus canker-affected leaves and chlorosis-infected leaves. Fluorescence spectroscopy can be used to analysed Nanomaterials. Fingerprints can be visualized with Fluorescent compounds such as ninhydrin or DFO(1,8-Diazafluoren-9-one). Blood & other substance are sometime detected by fluorescent reagents, like Fluorescein . Fluorescent colours are frequently used in road signs ,traffic and these colours are recognizable at longer ranges.

21. FLUORESCENT MATERIALS USES

22. QUENCHING When photochemically excited atom undergoes collision with another atom or molecule before it has chance to show fluorescence ,the intensity of fluorescent radiation may be diminished or stopped . Quenching may occur in two ways; When the activated molecules undergoes a chance from a singlet excited state to the triplet excited state ,that is called internal quenching. When the activated molecules collide with other molecules /quencher which are externally added species & transfer their energy to those molecule, that is called external quenching. A + h A * (activation) A * A + h (fluoroscence) A * A (internal quenching) A * + Q A + Q * (external quenching)  

23. PHOSPHORESCENCE When the incident light falls on certain substances, they emits visible radiations of different frequency and do not stop immediate as soon the light is cut off, this phenomenan is known as phosphorescence. The substance are called phosphorescent substances. It is simply a delayed fluorescence. In other words certain substances after being excited by absorption of visible or UV light, emits radiation for some time , even light source is removed. The time period of phosphorescence 10 -5 to 10 -3 s . S +h S 1 ISC T 1 S +h * Example: Glow in the dark stars , ZnS ,glowing point …etc.  

24. PHOSPHORESCENCE When incident light falls on a molecule which has spin multiplicity is 1, and the valence electron get excited don’t change their spin. Now the electron goes to the triplet state by change its spin multiplicity 3 , so the state is called triplet state and the process is called ISC. The chance of returning of molecules from T 1 to S are very poor ,hence the molecule stay in T 1 state for long time . This stay is called time lag. The molecule which succeed in passing back to S ,emit radiation and phosphorescence occurs.

25. APPLICATION OF PHOSPHORESCENCE Phosphorescence light is used on glowing suits by dancer. They use phosphorescence light because they have longer decay time than fluorescence light . Phosphorescence is used in items like toys , stickers ,paint ,and watch faces that glow after being exposed to bright light. The glow can last for minutes or hours in a dark room. Phosphorescence is used in radar screens to keep target “blips” visible as the radar beam rotate. Many common drugs , including Aspirin, Benzoic acid, Morphine, and Dopamine have phosphorescence properties .

26. CONCLUSION Jablonski diagram is a visual representation of the electronic states, vibrational levels and transition of molecule. Fluoroscence and phosphorescence are used in forensic, road signs, watches, glow sheets, shadow wall.