1. Molecular aggregates
Myounghee Lee

2. Nanoparticles stability of silole in acetone/water mixture
Blue-shift of PL peak & Decrease of PL intensity with time

3. J-Aggregates ? Red-shift of absorption spectra of TDBC in water at RT
Linear aggregate
Exciton model
Mirjam van Burgel, Douwe A. Wiersma, and Koos duppen, J. Chem. Phys. 2001, 102(1), 20.

4. J-Aggregates ? J-aggregates (or Scheibe aggregates)
named after one of its discorverers
E. E. Jelly & G. Scheibe in the late 1930s[1,2]
pseudo isocyanine (PIC)
Molecular aggregates formed by cyanine dye
Strongly coupled transition dipoles, Frenkel excitons
Geometrical arrangement, coupling energy
Splitting of excitation energy
one Molecule (M)
upper state allowed (H) : H-aggregate, parallel alignment
lower state allowed (J) : J-aggregate, oblique alignment
For more complex alignment,
splitting of the excitonic band into the several bands [3]
Excitonic energy states of monomer and dimers
[1] Scheibe, G. Angew. Chem. 1937, 50, 51.
[2] Jellly, E. E. Nature 1936, 138, 1009: Nature 1937, 139, 631.
[3] S. Kirstein, R. Steitz, R. Garbella and H. Möhwald J. Chem. Phys. 103(2) (1995) 815.

5. An example of H- and J-aggregates of a cyanine dye, DiSC3+(5)
1st splitting - stacking interaction bet. Cyanine dimers
2nd splitting - end-to-end interactions bet. dimers along the length of the H- and J-aggregates
Arindam Chowdhure, Sebastian Wachsmann-Hogiu, Prakriti R. Bangal, Izzat Raheem,
and Linda A. Peteanu, J. Phys. Chem. B 2001, 105,

6. Coupling energy and red-shift of J-aggregates
Quantum mechanical Hamiltonian of an unperturbed J-aggregate,
Resonant Coulomb-coupling energies of the system of
extended dipoles arranged on the hexagonal lattice,
Red-shift of the J-band in the observed spectra of the aggregate,
Bn+ and Bn - the creation and annihilation operators of the excited state of the molecule at the site n,
- the excitation energy of the corresponding monomers,
Dn - the energy shift due to the Electrostatic interaction of the monomers with the lattice,
Jn,m - the resonant coupling Energy between the chromophores at the site n and m,
l – extended dipole length (double charges of magnitude Q and moment, )
S. Engelhard and F. H. M. Faisal, J. Chem. Phys. 1999, 110, 3596.

7. Radiative Dynamics in solution and in molecular assemblies
of an H-aggregate-forming stilbazolium amphiphile
Q. Song, P. W. Bohn, and G. J. Blanchard
J. Phys. Chem. B 1997, 101, 8865

8. Kinetic diagram of the optical transition for a cyanine molecule
Hemicyanine - H-aggregate at air-water interface
The relaxation diagram of ground and
excited electronic potential surface
Samples used in this paper -
I. Monomer in solvents
II. H-aggregates in Langmuir-Blodgett (LB) films on SiO2
exciton hopping
intramolecular coupling for excited state
intermolecular coupling (energy transfer)
* Monolayer structure : aggregate islands (99.5%)with monomer (0.5%)
at grain boundaries and in the interstices

9. Frenkel Exciton
Exciton hopping
Energy transfer

10. Kinetic diagram of the optical transition for a cyanine molecule
Decay lifetime
Hemicyanine - H-aggregate at air-water interface
Size of aggregate e h
Samples used in this paper -
I. Monomer in solvents
II. H-aggregates in Langmuir-Blodgett (LB) films on SiO2
exciton hopping
intramolecular coupling for excited state
intermolecular coupling (energy transfer)
Monolayer structure : aggregate islands (99.5%)with monomer (0.5%)
at grain boundaries and in the interstices

11. Kinetic response in monomer
Time-dependent population changes for the energy level,
N0, N1, N2 – populations of the ground state, initially populated level, and the TICT state
The solution for this set of coupled linear differential equations has the form,
N10 – initial populations of the directly populated excited satate

12. Kinetic response in monomer
The signal observed is,
A single-exponential decay function is not sufficient to describe the fluorescence behavior
when reversible coupling exists between an emissive state and other excited electronic states.
The solution for this set of coupled linear differential equations has the form,
Using Taylor series expanding
Further simplification,

13. Lifetimes in n-Alkanol solutions
Excited at 480 nm and monitored at 660(+,-30) nm

14. Lifetimes in LB film

15. Kinetic diagram of the optical transition for molecules in various states
The relaxation diagram in mixed state of monomer and aggregates,
Time-dependent population changes for LB film,
A* : excited aggregate
M* : excited monomer
Kxt : rate of exciton transfer

16. Modeling of aggregate decay dynamics
Decreasing the nonradiative rate relative to the rate for exciton transport
- introduce rise time
Decreasing the rate of exciton transport
- produces weaker fluorescence
Fitting parameters

17. Monte Carlo simulation
Random walk model for exciton hopping
The distribution of the distance of the final positions from the origin
- runs ranging from 50 to 500 hops
Mean distance traveled for exciton diffusion as a
Function of the number of discrete steps taken
- the relation can be used to estimate the aggregate size

18. Monte Carlo simulation

19. The size of an H-aggregate
Fitting parameters
from the measured value,
average lifetime of exciton,
exciton hopping time for organic monolayers, typically very fast, ~0.1 ps
average distance traveled,
45 steps = 45 molecules
26.5 angstrom

20. Monte Carlo simulation
Blue area ?
1. randomly select a location within the rectangle 2. if it is within the blue area, record this instance a hit 3. generate a new location and repeat 10,000 times

21. LB film