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Design, Synthesis, and Proticity Inclined Conformational Modulation in a Highly Fluorescent Bichromophoric Naphthalimide Derivative: Hint Directed from RICT Perspective
journal contribution
posted on 2016-02-09, 17:05 authored by Ritika Joshi, Oinam Romesh Meitei, Himank Kumar, Manojkumar Jadhao, Sujit Kumar GhoshThe
present study embodies design, in silico DNA
interaction, synthesis of benzothiazole containing naphthalimide derivative,
2-(6-chlorobenzo[d]thiazol-2-yl)-1H-benzo[de] isoquinoline-1,3(2H)-dione (CBIQD) along with its systematic photophysics,
solvatochromic behavior, and solvation dynamics using an experimental
and theoretical spectroscopic approach. Steady-state dual emission
and biexponential fluorescence decay reveals the formation of two
different excited species. Ground- and excited-state optimized geometry
and the potential-energy curve obtained from DFT and TD-DFT calculation
ascertained the existence of nonplanar and planar conformation. When
the solvent polarity is changed from nonpolar to protic polar, the
feebly emissive emission band highly intensifies probably due to the
reversal of n, π*−π, π* emissive state along
with consequent modulation of their energy gap that is induced by
H-bonding. Excluding nonpolar solvents, in all other solvents, the
Stokes shift correlates linearly with orientation polarizability,
whereas in water, the story remains intriguing. With photoexcitation,
intermolecular H-bonding stimulates the pyramidalization tendency
of imide “N” with subsequent conformational change of
GS nonplanar geometry to a coplanar one through acceptor rehybridization
generating a rehybridized intramolecular charge transfer (RICT) state
that caused a dramatic fluorescence upsurge. This allosteric modulation
is promoted by excited-state H-bonding dynamics especially in strong
H-bond donor water. A close interplay between preferential solvation
and the proximity effect is evident in the emission behavior in a
benzene (Bn)–ethanol (EtOH) binary mixture. Molecular docking
analysis delineates considerable noncovalent sandwiched π–π
stacking interactions of CBIQD with the pyrimidine rings as well as
with imidazole rings of dG 6 and dG 2 base pairs of B-DNA double helix,
which probably suffices the design strategy adopted. Overall, a strategic
design to synthesize a highly fluorescent and potential bioactive
agent is executed to revolutionize the fluorophore field due its enormous
progressive importance in biochemical applications.
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Keywords
emissive emission bandfluorophore fieldsolvation dynamicssolvatochromic behaviorrehybridized intramolecular charge transferfluorescence upsurgeGS nonplanar geometrydG 6orientation polarizabilityallosteric modulationCBIQDnonpolar solventsdG 2 base pairsacceptor rehybridizationProticity Inclined Conformational Modulationpyramidalization tendencydesign strategypyrimidine ringsimidazole ringsDFTspectroscopic approachStokes shift correlatesbioactive agentemission behaviorbiexponential fluorescence decayRICT PerspectiveTheenergy gapMolecular docking analysis delineatesFluorescent Bichromophoric Naphthalimidesilico DNA interactionproximity effect
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