Macroscopic Molecular Ordering and Exciton Delocalization in Crystalline Phthalocyanine Thin Films.
We present spatially-, temporally- and polarization-resolved dual photoluminescence/linear dichroism microscopy experiments that investigate the correlation between long-range order and the nature of exciton states in solution-processed phthalocyanine thin films. The influence of grain boundaries and disorder is absent in these films because typical grain sizes are 3 orders of magnitude larger than focused excitation beam diameters. These experiments reveal the existence of a delocalized singlet exciton, polarized along the high mobility axis in this quasi-1D electronic system. The strong delocalized π orbitals overlap, controlled by the molecular stacking along the high mobility axis, is responsible for breaking the radiative recombination selection rules. Using our linear dichroism scanning microscopy setup, we further established that a rotation of molecules (i.e., a structural phase transition) that occurs above 100 K prevents the observation of this exciton at room temperature.
Naveen
N
Rawat
Zhenwen
Z
Pan
Lane W
LW
Manning
Cody J
CJ
Lamarche
Ishviene
I
Cour
Randall L
RL
Headrick
Rory
R
Waterman
§Cornell High Energy Synchrotron Source, Cornell University, Ithaca, New York 14853, United States.
Arthur R
AR
Woll
Madalina I
MI
Furis
grain boundaries; linear dichroism imaging; long range order; peripheral substituted phthalocyanines; solution processing