INFLUENCE OF PERIPHERAL PHENYLS TO EXCITED STATE
RELAXATION AND AGGREGATION INDUCED FLUORESCENCE IN
NITRILE COMPOUNDS
Gintarė Kuksėnaitė1, Karolis Kazlauskas1, Gediminas Kreiza1, Arūnas Miasojedovas1,
Paulius Baronas1, Aurimas Bieliauskas2, Vytautas Getautis2, Algirdas Šačkus2, Saulius Juršėnas1
1
Institute of Applied Research, Vilnius University, Lithuania
Faculty of Organic Chemistry, Kaunas University of Technology, Lithuania
[email protected]
2
Fluorescent nanoparticles attract great interest in the field of technological applications. They were found to be
suitable for constructing OLEDs, OFETs and other optoelectronic systems. They are also fit for tailoring biological
probes for bio-sensing and bio-imaging. Fluorescent organic nanoparticles are usually composed of non-planar
geometry molecules experiencing the aggregation induced emission (AIE) phenomenon. [1]
Three nitrile-based compounds with different number of peripheral phenyl moieties are studied in this work
(Fig. 1). The compounds are designed to show AIE properties. The cyano-vinylene bridge is intentionally introduced
into the core to provide a steric twist in the molecules. The pyrazole groups have the ability to deliver high fluorescence
efficiency in addition to causing strong intermolecular hydrogen bonds and π-π interactions, which are important for
supramolecular constructions. [2]
Nanoparticles based on the nitrile compounds have been formed using precipitation method. The compounds are
non-fluorescent in diluted solutions, but demonstrate induced emission upon aggregate formation. The nitrile compound
containing no peripheral phenyls demonstrated broad absorption and fluorescence spectra in aggregated state. It also
exhibited an amorphous aggregate structure in the neat film and a moderate (10-fold) emission enhancement as
compared to that in solution. The compound with two peripheral phenyl rings featured 100-fold emission enhancement
in the solid phase, which was accompanied by vibronically-resolved spectrum of aggregates indicating their crystalline
nature. The nitrile compound bearing four peripheral phenyls showed similar features as the compound with two phenyl
moieties. Thus, the peripheral phenyl groups in turn affected the morphology of nitrile-based nanoaggregates formed by
precipitation method.
Fig. 1. The chemical structures of investigated compounds.
Optical properties of the compounds assessed in diluted solutions revealed that peripheral phenyl rings improve
compound conjugation and significantly shortens excited state radiative decay time. Interestingly, the peripheral
phenyls were found to not affect non-radiative decay time. It was also deduced that the central phenyl moiety is the
main source of intramolecular vibrations/torsions, and therefore, is responsible for extremely weak fluorescence
quantum yield in solutions.
[1] J. Mei, N. L. C. Leung, R. T. K. Kwok, J. W. Y. Lam, ir B. Z. Tang, „Aggregation-Induced Emission: Together We Shine, United We Soar!“,
Chem. Rev., t. 115, nr. 21, p. 11718–11940, 2015.
[2] K. Kazlauskas et al., „Morphology and emission tuning in fluorescent nanoparticles based on phenylenediacetonitrile“, J. Phys. Chem. C, t. 118,
nr. 43, p. 25261–25271, 2014.