  Pyrene based molecules are inclined to form excimers through self-association
upon photoexcitation. In this work, the pyrene core is functionalized with
N-methylacetamide group at the position 1 or 2, to develop
pyren-1-methylacetamide (PyMA1) and pyren-2-methylacetamide (PyMA2),
respectively. Upon photoexcitation, PyMA1 and PyMA2, at 1.0mM, in toluene, have
formed predominantly static excimers. The steady state spectroscopic studies
have showed that the excitonic coupling of PyMA1 dimers are much stronger in
solution than its isomeric counterpart, PyMA2. The transient absorption (TA)
measurements over fs-ps regime (fs-TA) showed that the formation of static
excimers with the strongly-coupled pre-associated dimers, in PyMA1, happens in
approx. 560fs, whereas, the excimers for the weakly-coupled pre-associated
dimers in PyMA2 have formed in much slower time scale (approx. 65ps). The
introduction of methylacetamide group at the position 1 or 2 on pyrene ring,
was believed to have allowed forming hydrogen bonded excimers with different
degrees of excitonic coupling.
