Transcript 1-phenylpyrrole_090622.ppt

1-Phenylpyrrole: A TICT
Molecule?
Jessica A. Thomas, Justin W. Young,
Adam J. Fleisher, Casey L. Clements,
and David W. Pratt
University of Pittsburgh
Leonardo Alvarez-Valtierra
Universidad de Guanajuato
What is TICT?
• Twisted intramolecular charge transfer
– Movement of e- density leads to change in excited
state conformation
Example: DMABN
E. Lippart, W. Lüder, and H. Boos, in the Proceedings
of the 4th International Meeting on Advances in
Molecular Spectroscopy (1959), A. Mangini, ed.,
Pergamon Press, Oxford, 1962, pgs. 443-457.
TICT Molecule?
– Condensed phase
• Shows dual fluorescence
– SVLF
• S1 is more planar than S0
– Theory
• Identified state with large dipole moment &
perpendicular configuration
– High resolution
K. Okuyama et al, J. Chem. Phys. 109, 7185 (1998) and references therein.
B. Proppe et al, J. Phys. Chem. A. 104, 1608 (2000).
Or More Like Biphenyl?
DMABN
(TICT)
Dual fluores. (red shift)
Double ring
Amino group
Torsion progression
1PP
Biphenyl
(no TICT)
Vibrationally Resolved Spectrum
4.5
4.5
4
3.5
3
4
3.5
2.5
2
1.5
3
2.5
1
2
0.5
0
35400
1.5
35600
1
35800
36000
36200
36400
36600
Wavenumbers (cm -1)
0.5
0
35400
35600
35800
36000
36200
36400
36600
Wavenumbers (cm -1) J. Murakami, M. Ito, and K. Kaya, J. Chem.
K. Okuyama et al, J. Chem. Phys. 109, 7185 (1998).
Phys., 74, 6505 (1981).
Rotationally Resolved Spectrum
p-branch
r-branch
Additional
band or
subband
q-branch
~4 cm-1
~ 0.1 cm-1
Rotational Constants
Ground
State
Excited
State
Difference
A (MHz)
3508.3(1)
3379.0(1)
-129.3
B (MHz)
703.3(1)
710.3(1)
7.1
C (MHz)
604.7(1)
595.3(1)
-9.4
ΔI (amu Å2)
-26.86
-12.02
14.84
Torsion
Angle
30˚
25˚
-5˚
(MP2/6-311g)
a/b/c
0/85/15
Transition Moment
a
a
a
b
b
b
Pyrrole
a - type
Aniline
Primarily b - type
(some c due to
twist)
b - type
Electronic Excitation
• Electron density moves
from pyrrole to phenyl
• C-N bond order increases
• Molecule becomes more
rigid along torsion
coordinate
• Torsion angle is smaller
MP2/6-311g
LUMO
HOMO
Summary
• Structural Information:
– Transition moment corresponds to phenyl excitation
– Molecule becomes more planar upon excitation
– Electron density is transferred from pyrrole to phenyl
• Conclusions:
– Okuyama et al assessment correct
– More data are needed to confirm/exclude additional
TICT state
Future Work
• TICT character
– Water complexes: is new excited state accessible in
presence of polar solvent?
– Stark: dipole moment of excited state?
• Vibrations
– Additional bands: different ground state rotational
constants?
– Identity of A01 vibration?
Acknowledgements
The Pratt Group:
We gratefully acknowledge support from
NSF.