山东大学：《物理化学》课程教学资源（讲义资料）10.6 Photochemical reaction-12-for students

810. 6 Photochemistry It-class reading Levine, pp. 800-804 photochemistry

§10. 6 Photochemistry Out-class reading: Levine, pp. 800-804 photochemistry

§10.6 Photochemistry 6.1 Brief introduction of light 1)Photochemistry The branch of chemistry which deals with the study of chemical reaction initiated by light 2) Energy of photon The photon is quantized energy: light quantum ho Where h is the Plank constant, C the velocity of light in vacuum, a the wave-length of the light, and v the wave number

6.1 Brief introduction of light The branch of chemistry which deals with the study of chemical reaction initiated by light. 1) Photochemistry The photon is quantized energy: light quantum     hC C = h = h = Where h is the Plank constant, C the velocity of light in vacuum,  the wave-length of the light, and  the wave number. 2) Energy of photon §10. 6 Photochemistry

§10.6 Photochemistry 6.1 Brief introduction of light 3×105m3.98×108kJmo1 radIo s=h 3×101m3.98×104 kJ mol1 micro-wavel 6×104m199×101 k mol1 Microwave Ifar-infrared I chemistry 3×105m3.99 k. mol1 Inear-infrared 800 nm 149.5 kJ mol-1 visible 400 nm 299.0 kj mol-1 photochemistry lultra-violet I 150 nm 797.9 kj mol-1 vacuum violet 50nm239×104 kJ mol1 radiochemistry 5nm1.20×109 kJ mol1 I X-ray

6.1 Brief introduction of light §10. 6 Photochemistry

§10.6 Photochemistry 6.1 Brief introduction of light 1: intensity of light, 4)Interaction between light and media d I adx x: the thickness of the medium a: the absorption coefficient absorption Light transmission I=loxp(ax) beam Lambert’slaw Reflection Scattering refraction I=lo[1-expax)] d Beer’slaw: lo exp(-acx

4) Interaction between light and media exp( ) I = I0 −ax adx I dI − = [1 exp( )] I I0 I I0 ax a = − = − − I: intensity of light, x: the thickness of the medium, a: the absorption coefficient. 6.1 Brief introduction of light Beer’s law: 0 exp( ) a I I cx = − Lambert’s law §10. 6 Photochemistry Light beam

§10.6 Photochemistry 6.2 Physical processes of Excitation and decay (1)Photoexcitation Upon photo irradiation, the molecules or atoms can be excited to a higher vibrational or rotational states Electronic Excitation of x-x A+hy→A Excited state The lifetime of the excited atom is of the Ground state order of 10-8s. Once excited, it decays at nce A absorption F=fluorescence IR spectrum

Upon photo irradiation, the molecules or atoms can be excited to a higher electronic, vibrational, or rotational states. A + h → A* The lifetime of the excited atom is of the order of 10-8 s. Once excited, it decays at once. IR spectrum 6.2 Physical processes of Excitation and decay (1) Photoexcitation: §10. 6 Photochemistry

§10.6 Photochemistry 6.2 Physical processes of Excitation and decay (1)Photoexcitation: Efficiency of Anti-Stokes Fluorescence in Dyes AccoRDING to Kautsky and his collaborators, the majority of the molecul les of dyos investigated by them, anong which were also the molecules of fluoresceine, show an ability to phosphoresce when energetically isolated,, for example, when adsorbed by convenient adsorbents e can assume therefore Va M vvvv 3210 N vels in phorescent molecule on to metastable lev( The Foundation of a typical Jablonski diagram nall transition probabil scence, g-absorption of A Jablonski, Efficient of Anti-Stokes Fluorescence in Dyes Nature,1933,Jun.10,839-840

The Foundation of a typical Jablonski Diagram (1) Photoexcitation: 6.2 Physical processes of Excitation and decay §10. 6 Photochemistry A. Jablonski, Efficient of Anti-Stokes Fluorescence in Dyes, Nature, 1933, Jun. 10, 839-840

§10.6 Photochemistry 6.2 Physical processes of Excitation and decay (1)Photoexcitation Internal conversion Absorbance Vibrational relaxation and Internal Conversion 2 Insystem conversion Intersystem Crossing Fluorescence absorption I T Phosphorescence i/ fluorescence v absorption 光子光激发基态激发态能级能带雅布 phosphorescence 隆斯基( Jablonski)图激发态衰变振动弛 豫内转换系间穿越辐射跃迁无辐射跃迁 rotational vibration state 单线态三线态荧光磷光 state 0 ground state Jablonski diagram

Jablonski diagram 6.2 Physical processes of Excitation and decay (1) Photoexcitation: §10. 6 Photochemistry Absorbance Vibrational Relaxation and Internal Conversion Intersystem Crossing Fluorescence Phosphorescence 光子 光激发 基态 激发态 能级 能带 雅布 隆斯基（Jablonski）图 激发态衰变 振动弛 豫 内转换 系间穿越 辐射跃迁 无辐射跃迁 单线态 三线态 荧光 磷光

§10.6 Photochemistry 6.2 Physical processes of Excitation and decay (1)Photoexcitation Radiation-less decay Which is which? radiation v fluorescence ground state singlet ground state radiation 八八、 phosphorescence 4005006007008009001000 Wavelength(nm) ground state 大

Radiation-less decay Which is which? 6.2 Physical processes of Excitation and decay (1) Photoexcitation: §10. 6 Photochemistry

§10.6 Photochemistry 6.2 Physical processes of Excitation and decay (1)Photoexcitation Transition Time Scale Radiative Process? Internal Conversion 10 -14 10 no 14 Vibrational relaxation 10 -10s no 15 Absorption 10s yes Phosphorescence 10-10s yes Intersystem Crossing 10°10s no Fluorescence 10-10s yes https://chem.libretexts.org/textbook_maps/physical_andtheoreticAlChemistryTextbook_maps/suppl emental_ Modules_(Physical and_ Theoretical_ Chemistry)/Spectroscopy/Electronic_ Spectroscopy/Jablo ski diagram

Transition Time Scale Radiative Process? Internal Conversion 10-14 - 10-11 s no Vibrational Relaxation 10-14 - 10-11 s no Absorption 10-15 s yes Phosphorescence 10-4 - 10-1 s yes Intersystem Crossing 10-8 - 10-3 s no Fluorescence 10-9 - 10-7 s yes 6.2 Physical processes of Excitation and decay (1) Photoexcitation: §10. 6 Photochemistry https://chem.libretexts.org/Textbook_Maps/Physical_and_Theoretical_Chemistry_Textbook_Maps/Suppl emental_Modules_(Physical_and_Theoretical_Chemistry)/Spectroscopy/Electronic_Spectroscopy/Jablo nski_diagram

§10.6 Photochemistry 6.2 Physical processes of Excitation and decay (2) Decay of photoexcited molecules Radiation transition Fluorescence and phosphorescence non-reactive decay Radiationless Vibrational cascade and thermal transition energy decay Reaction of excited molecule A"→P reactive deca Energy transfer A+Q→>Q→P

(2) Decay of photoexcited molecules decay non-reactive decay reactive decay Radiation transition Radiationless transition Fluorescence and phosphorescence Vibrational cascade and thermal energy Reaction of excited molecule A* → P Energy transfer: A* + Q → Q* → P 6.2 Physical processes of Excitation and decay §10. 6 Photochemistry