Transcript OSU_DB15C5_2.ppt

CONFORMATION-SPECIFIC ELECTRONIC AND
VIBRATIONAL SPECTROSCOPY OF DIBENZO-15CROWN-5 ETHER IN A SUPERSONIC JET.
Evan Buchanan, Chirantha P. Rodrigo, William H. James, Josh J. Newby,
and Timothy S. Zwier
Department of Chemistry, Purdue University
West Lafayette, Indiana
15-Crown-5 Ethers
Motivation:

Crown ethers provide a chemical means to
preferentially sequester substrates, especially
cations.

Model enzyme-substrate interactions

Conformational consequence of adding a second
benzene ring. How flexible is the macrocycle?

Where is the second excited state?

Investigate the electronic energy transfer
between the two chromophores..
Dibenzo-15-crown-5 (DB15C)
Benzo-15-crown-5 (B15C)
J.-M. Lehn. Pure & Appl. Chem., 1979, 51, 979
R. Kusaka, Y. Inokuchi, T. Ebata. Phys. Chem. Phys., 2007, 9, 4452
Supersonic Expansion
MCP
Pulsed valve
 Large, flexible molecule
with many conformational
isomers is entrained in a
high pressure backing gas.
 Gas expands through a
pinhole into a vacuum.
 Molecules collisionally cool
with the buffer gas
 Expansion reduces the number of transitions observed in the spectra
 Rotational temperature of a few Kelvin
 Vibrational temperature of 10-20 Kelvin.
Experimental Methods
Resonant Two-Photon
Ionization
UV-UV Holeburning
Ionization Continuum
Ionization Continuum
Molecule + + e-
Molecule + + e-
Sn
Spatially overlapped
Δt = 200 ns
Sn
S0
S0
A
A
B
B
R2PI: Electronic Spectrum
UVHB: Conformation specific electronic
spectrum
LIF and UVHB Spectra of B15C
DMB

DEB
Three conformers
present in the jet
expansion.
LIF
A


One conformer blue
shifted by over 500
cm-1.
S0 – S1 origin serve as
a sensitive probe of
the local environment
about the phenyl ring.
*
B
*
*
C
B15C5-H2O
35600 35800 36000 36200 36400 36600 36800 37000 37200
V. A. Shubert et al. J. Phys. Chem. In press.
R. Kusaka, Y. Inokuchi, T. Ebata. Phys. Chem. Chem. Phys., 2007, 9, 4452
Something Simpler: 1,2-diethoxybenzene
γ
Carbon Position
β
β
γ
Relative Origin (cm-1)*
in/in
in/in
0
in/in
in/out
-480
out/in
in/in
343
in/in
out/out
-800 to -900
out/in
in/out
38 to 53
out/out
in/in
1286
* TDDFT predicted S0 – S1 origins
B15C conclusions:

Conformers A, and B: in/in; in/in

Conformer C: out/in; in/in
B15C Assigned Structures
1.5 KJ/mol
0.0 KJ/mol
B15CA): in/in; in/in
B15C(C): out/in; in/in
B3LYP/6-31+G(d)
7.1 KJ/mol
B15C(B): in/in; in/in
Can we use the same technique to
assign the local environment for DB1C?
R2PI and UVHB Spectra of DB15C
R2PI
A
35600
*
B
*
*
(S1 vibronic levels)
35632
C
35624
D
36127
*
B15C
35600



35800
36000
36200
-1
Wavenumbers (cm )
36400
36600
Three conformers indicative of in/in; in/in structures for ring 1.
Blue shifted conformer indicative of an out/in; in/in structure for ring 1.
Position of S2 in A, B, and C is not clear.
Resonant Ion-dip Infrared Spectroscopy
Δt = 50-200 ns
Ionization Continuum
B+ + e-
IR spatially overlapped
Sn
S0
UV only
IR and UV
A
B
Active Baseline
Subtraction
RIDIRS: Conformation specific IR S0 spectrum
Alkyl C-H Stretch Spectra
A
C(x3)
B
D
2800
2850
2900
-1
Wavenumbers (cm )
2950

Spectral congestion due to 14 C-H stretch fundamentals.

Transitions above 2930 cm-1 indicative of CH…O interactions and the
degree of buckling of the crown.
3000
Where is the S2 Origin?
B
109
S1
35600
DB15C
35650
35700
35750
35800
B15C

Unusually large transition occurring at +109.

Possible S2 origin?
35850
35900
35950
All planar region
DFL Conformer B
B origin
0
500
1000
-1
Relative Energy (cm )
1500
Carbon Position
β
γ
Relative Origin (cm-1)*
in/in
in/in
0
in/in
in/out
-480
out/in
in/in
343
in/in
out/out
-800 to -900
out/in
in/out
38 to 53
out/out
in/in
1286
109
Internal Mixing
0
0
S2
0
500
1000
-1
Relative Energy (cm )
1500
{S1(ν)}
Where is the S2 origin?
D
24
72
48
36120
DB15C
36160
36200
36280
36240
B15C
36320
36360
36400
+500 cm-1 from conf. A,B, and C.

Similar vibronic structure to B15C.

Extra transitions could be the S2 origin.

Out/in; in/in structure for both rings.
DFL Conformer D
D origin
+ 25
+ 48
+ 72
0
500
1000
-1
Relative Energy (cm )
1. Two overlapping transitions under holeburn transition
2. Two stable excited state minima for each ring.
1500
Future work

Acquire more DFL to identify the S0 – S2 origin and probe electronic coupling
between states.

Water clusters: B15C distorts the crown to accommodate
hydrogen bonding with water. Does DB15C behave in a
similar manner?

SEP-PT: measure barriers to isomerization.
 How flexible is the crown?
 How does it depend on one vs. two rings?
Acknowledgements
Prof. Timothy S. Zwier
Current Group Members:
Past Group Members:
Dr. Christian W. Müller
William H. James
Josh J. Newby
Chirantha P. Rodrigo
Josh A. Sebree
Zachary Davis
James Redwine
Ryan Muir
Deepali Mehta
Dr. Tracy LeGreve
Dr. Nathan Pillsbury
Dr. Alvin Shubert
Dr. Esteban Baquero
Computational Resources:
Information Technology at Purdue (ITaP)
Funding:
National Science Foundation