Spectroscopic properties of aromatic dicarboximides part 3: Substituent effect on the photophysical properties of N-phenyl-2,3-napthalimides

sp3 C-H Arylation and Alkylation Enabled by the Synergy of Triplet Excited Ketones and Nickel Catalysts

Triplet ketone sensitizers are of central importance within the realm of photochemical transformations. Although the radical-type character of triplet excited states of diaryl ketones suggests the viability for triggering hydrogen-atom transfer (HAT) and single-electron transfer (SET) processes, among others, their use as multifaceted catalysts in C-C bond-formation via sp³ C-H functionalization of alkane feedstocks still remains rather unexplored. Herein, we unlock a modular photochemical platform for forging C( sp³)-C( sp²) and C( sp³)-C( sp³) linkages from abundant alkane sp³ C-H bonds as functional handles using the synergy between nickel catalysts and simple, cheap and modular diaryl ketones. This method is distinguished by its wide scope that is obtained from cheap catalysts and starting precursors, thus complementing existing inner-sphere C-H functionalization protocols or recent photoredox scenarios based on iridium polypyridyl complexes. Additionally, such a platform provides a new strategy for streamlining the synthesis of complex molecules with high levels of predictable site-selectivity and preparative utility. Mechanistic experiments suggest that sp³ C-H abstraction occurs via HAT from the ketone triplet excited state. We believe this study will contribute to a more systematic utilization of triplet excited ketones as catalysts in metallaphotoredox scenarios.

Design, Synthesis, and Proticity Inclined Conformational Modulation in a Highly Fluorescent Bichromophoric Naphthalimide Derivative: Hint Directed from RICT Perspective

The 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.

Excimer–monomer switch: a reaction-based approach for selective detection of fluoride

Desilylation triggered excimer–monomer switch based on 1,8-naphthalimide was used as a sensing strategy for detection of fluoride.

A new N-imidazolyl-1,8-naphthalimide based fluorescence sensor for fluoride detection

A chemosensor is reported with high sensitivity and selectivity for detection of fluoride anion. The recognition mechanism is attributed to a fluoride-triggered disruption of the hydrogen bond between imidazole and naphthalimide moieties, resulting in a noncoplanar geometry with low fluorescence.

Toward intrinsically fluorescent proteomimetics: fluorescent probe response to alpha helix structure of poly-gamma-benzyl-L-glutamate

A fluorescent probe (1), developed for recognition of alpha helical secondary structure, shows a large fluorescence change upon titration with the synthetic protein PBLG. Compared to fluorophores of similar size and shape, 1 displayed the smallest dissociation constant (K(D)=80microM) when titrated with PBLG. These preliminary studies are directed toward developing small molecule proteomimetics that have intrinsic fluorescence and are specific for helical-protein binding-sites.

Matrix Screening of Substituted N-Aryl-1,8-naphthalimides Reveals New Dual Fluorescent Dyes and Unusually Bright Pyridine Derivatives

A 3 x 14 matrix of substituted N-aryl-1,8-naphthalimides was synthesized for the evaluation and discovery of dual fluorescence. Because of their unique photophysical properties, these dual fluorescent systems represent an exception to the widely studied TICT (Twisted Internal Charge Transfer) fluorescent dyes or tautomeric benzofluorescein class of two-color dyes. The matrix library was designed to investigate the effects of heterocycles, particularly pi-excessive and pi-deficient systems. Of the 42 compounds surveyed, five displayed well-resolved two-color emission in solvents as nonpolar as hexane. Based on the observed trends in fluorescence lambda(max) and quantum yield, a new model is proposed that predicts LW and SW emission for these systems. In addition, this model provides potential design features for the synthesis of new dual fluorescent species.

Pressure dependence of the dual luminescence of twisting molecules. The case of substituted 2,3-naphthalimides

The effect of high pressure (up to 5 kbar) has been studied for triacetin solutions of 2-phenyl-2,3-dihydro-1H-benzo[f]isoindole-1,3dione 1 (N-phenyl-2,3-naphthalimide) and its 3-fluorophenyl- (2), 4-carbethoxyphenyl(4) and 4-methoxyphenyl (5) derivatives which all show dual fluorescence. When the N-phenyl group is unsubstituted (compound 1) or substituted with electron-attracting groups (2 and 4), the increase of pressure over the solution decreases slightly the emission at the long-wavelengths (LW) and increases dramatically the intensity of the short-wavelength (SW) fluorescence. Plotting the logarithm of the SW/LW fluorescence quantum yield ratio for compounds, 1,2 and 4 versus the logarithm of the viscosity of the medium shows a substantial increase of this ratio which corresponds mainly to the increase of the SW emission intensity, the effect on the LW emission being only moderate. As the pressure is increased, the rotation of the N-phenyl group of compound 1 is progressively hindered and the prevailing emission comes from a state which has the same geometry as the ground state (in which the planes of the two moieties of the molecule form an angle close to 60 degree). The effect is different when an electron-donating methoxy group is attached in the para position to the N-phenyl ring, compound 5, as mainly the LW fluorescence intensity increases with pressure. For this molecule which has an electron-donating p-substituent on the N-phenyl ring, the two moieties of the ground state molecule have a more planar geometry (43 degree angle) and the LW fluorescence appears to originate from an intramolecular charge transfer state the fluorescence of which increases with pressure. A three-level reaction scheme is proposed to account for the observed kinetics. In all cases, the viscosity of the medium is found to be the main factor which induces the changes in the fluorescence spectra, and the deceleration of the non-radiative deactivation from the SW* excited state is responsible for these modifications whether a reversible process between the two emitting SW* and LW* states is observed (as for compounds 2 and 4) or not (as for compound 1).