Experimental and Theoretical
Study on the One- and
Two-Photon Absorption Properties of Novel Organic Molecules Based
on Phenylacetylene and Azoaromatic Moieties
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Abstract
This Article reports a combined experimental and theoretical
analysis
on the one and two-photon absorption properties of a novel class of
organic molecules with a π-conjugated backbone based on phenylacetylene
(<b>JCM874</b>, <b>FD43</b>, and <b>FD48</b>) and
azoaromatic (<b>YB3p25</b>) moieties. Linear optical properties
show that the phenylacetylene-based compounds exhibit strong molar
absorptivity in the UV and high fluorescence quantum yield with lifetimes
of approximately 2.0 ns, while the azoaromatic-compound has a strong
absorption in the visible region with very low fluorescence quantum
yield. The two-photon absorption was investigated employing nonlinear
optical techniques and quantum chemical calculations based on the
response functions formalism within the density functional theory
framework. The experimental data revealed well-defined 2PA spectra
with reasonable cross-section values in the visible and IR. Along
the nonlinear spectra we observed two 2PA allowed bands, as well as
the resonance enhancement effect due to the presence of one intermediate
one-photon allowed state. Quantum chemical calculations revealed that
the 2PA allowed bands correspond to transitions to states that are
also one-photon allowed, indicating the relaxation of the electric-dipole
selection rules. Moreover, using the theoretical results, we were
able to interpret the experimental trends of the 2PA spectra. Finally,
using a few-energy-level diagram, within the sum-over-essential states
approach, we observed strong qualitative and quantitative correlation
between experimental and theoretical results