Quiz 3

Question 1

n –> π* shifted to ______ wavelength (hysochromic shift)

Answer 1

shorter

Question 2

π –> π* shifted to _______ wavelength (bathochromic shift)

Answer 2

longer

polarization lowers energy of excited state more than ground state

Question 3

What is molecular luminesence?

Answer 3

emission of light from excited state of molecule

Question 4

What is photoluminescence?

Answer 4

excitation by absorption of photons

M + hv –> M*

Question 5

Photoluminesence emission is ______ wavelength than radiation used for excitation.

Answer 5

longer

Question 6

What is chemiluminesence?

Answer 6

based upon emission spectrum of an excited species that is formed during the course of a chemical reaction

Question 7

Two unpaired electrons results in a ______ state.

Answer 7

triplet

Question 8

The first excited triplet state is usually ______ in energy than the first excited singlet state.

Answer 8

lower

Question 9

Moelcules with unpaired electron systems are called ________.

Answer 9

paramagnetic

Question 10

What is internal conversion?

Answer 10

energy transition from second excited singlet state to first excited singlet state.

S₂ –> S₁

Question 11

What is intersystem crossing?

Answer 11

energy transition from first excited singlet state to first triplet state

S₁ –> T₁

Question 12

Fluoresence is when an electron is excited to ______ state, and then relaxes back down to the _______ state.

Answer 12

S₁, ground

Question 13

Phosphoresence is when an electron is excited to the ______ state, then proceeds to the _______ state through intersytem conversion, then relaxes back down to the _______ state.

Answer 13

S_1, T₁, ground

Question 14

Dissociation

Answer 14

the absorbed photons are of high enough energy that they can directly excite a molecular bond with sufficient vibrational energy to lead directly to bond rupture

Question 15

Predissociation

Answer 15

internal conversion ends up in dissociative electronic state or in a highly vibrationally excited lower electronic state, the bond breaks and the molecule dissociates

Question 16

How fast does adsorption happen?

Answer 16

10^-14 - 10^-15 s

Question 17

How fast are the singlet excited state lifetimes?

Answer 17

10^-7 - 10^-9 s

Question 18

How fast are excited triplet state lifetimes?

Answer 18

10^-4 - 10 s

Question 19

What is quantum yield?

Answer 19

the ratio of the number of molecules that luminesce to the total number of excited molecules

Question 20

Fluorescence most often is _______ since these transitions have larger probability and lower energy

Answer 20

π* –> π

Question 21

The most intense and useful fluorescence is found in compounds containing ______ rings with low ______ transition levels.

Answer 21

aromatic, π* –> π

Question 22

Heavy halo substitution ______ fluorescence through increased intersystem crossing and __________.

Answer 22

lowers, predissociation

Question 23

Fluorescence ________ with increasing temperature.

Answer 23

decreases

Question 24

When several resonance forms are possible for one form of the molecule, its fluorescence is ________.

Answer 24

increased

Question 25

Dissolved oxygen ______ fluorescence.

Answer 25

suppresses

Question 26

What is self quenching?

Answer 26

at high concentration

two excited molecules collide with each other, resulting in radiationless energy transfers, which leads to external conversion that suppresses fluorescence

Question 27

Fluorescent power is proportional to?

Answer 27

the power of the incident light source

F = K’(P₀ - P)

Question 28

K increases with ______ incident power.

Answer 28

increasing

Question 29

______ takes place at high concentration, thus linearity is lost.

Answer 29

self quenching

Question 30

Linearity is lost when adsorption is > than _____.

Answer 30

0.05

Question 32

What is external conversion?

Answer 32

where deactivation of an excited electronic state may involve interaction and energy transfer between the excited molecule and the solvent or other solutes

Question 33

What is the equation for quantum yield?

Answer 33

where k_f = fluorescence, k_i = intersystem crossing

k_ic = internal conversion, k_ec = external conversion

k_pd = predissociation, k_d = dissociation

Question 34

Substitution of a carboxylic acid or carbonyl group on a aromatic ring generally ______ fluorescence.

Answer 34

inhibits

Question 35

What is another way to write the equation of fluorescence power?

Answer 35

F = K’P₀(1 - 10^-ςbc)

F = 2.303K’ςbcP₀

Question 36

Dynamic quenching requires ________

Answer 36

contact between the excited species and the quenching agent(Q).

Question 37

For external conversion controlled by dynamic quenching with a single quencher, the external conversion rate constant can be written as _______

Answer 37

k_ec = k_q[Q]

where k_q = rate constant for quenching

[Q] = concentration of the quencher

Question 38

Polar solvents affects the ______

Answer 38

n–>π* and π–>π*

Question 39

Many inorganic compounds show UV absorption due to ________

Answer 39

n–>π* transition

Question 40

Absorption occurs when electron is transferred from the ______ to the _______.

Answer 40

donor, acceptor