Photoinduced intramolecular charge transfer in planar vs. twisted donor-acceptor terphenyls

Phenylpyridyl-Fused Boroles: A Unique Coordination Mode and Weak B-N Coordination-Induced Dual Fluorescence

Using 4-phenylpyridine or 2-phenylpyridine in place of biphenyl, two electron-poor phenylpyridyl-fused boroles, [TipPBB1]4 and TipPBB2 were prepared. [TipPBB1]4 adopts a unique coordination mode and forms a tetramer with a cavity in both the solid state and solution. The boron center of TipPBB2 is 4-coordinate in the solid state but the system dissociates in solution, leading to 3-coordinate borole species. Compared to its borafluorene analogues, the electron-accepting ability of TipPBB2 is largely enhanced by the pyridyl group. TipPBB2 exhibits dual fluorescence in solution due to an equilibrium between free TipPBB2 and a weak intermolecular coordination adduct with a second molecule. This equilibrium was further investigated by low-temperature NMR spectroscopy and photophysical studies. Theoretical studies indicate that the highest occupied molecular orbital (HOMO) of TipPBB2 localizes at the Tip group, in contrast to its borafluorene derivatives, wherein the HOMOs are localized on the borafluorene cores.

meta-Terphenyl linked donor–π–acceptor dyads: intramolecular charge transfer controlled by electron acceptor group tuning

A series of meta-terphenyl linked donor–π–acceptor (D–π–A) dyads were prepared to understand the electronic effects of a meta-terphenyl linker according to the electron-accepting ability change. The energy band gaps of the dyads were controlled by tuning the accepting ability, which resulted in emission colors ranging from blue-green to red. In the Lippert–Mataga plots, intramolecular charge transfer (ICT) behavior was observed, which showed gradually increased ICT characteristics as the accepting ability was increased. On the other hand, in the absorption spectra, a red shift of the ICT transition was observed differently from the electron-accepting ability tendency. Thus, the experimental results show that the ICT is determined by steric hindrance rather than the acceptor ability in the ground state due to the lack of π-conjugation of the terphenyl linker by the electron node in the meta-position, whereas ICT in the excited state is controlled by electron-accepting ability.

Dyads were prepared to understand the electronic effects of a meta-terphenyl linker according to the accepting ability change. The charge transfer properties in the ground/excited state are determined by accepting ability and/or steric hindrance.

Terphenyl backbone-based donor–π–acceptor dyads: geometric isomer effects on intramolecular charge transfer

The molecular geometry effects of ortho, meta, and para-terphenyl based donor–π–acceptor (D–π–A) dyads on intramolecular charge transfer (ICT) were studied to investigate structure-ICT relationships.

Solvent-sensitive circularly polarized luminescent compounds bearing a 9,9′-spirobi[fluorene] skeleton

Chiral 9,9′-spirobi[fluorene] derivatives with a donor–π–acceptor system were prepared and found to exhibit solvent-sensitive circularly polarized luminescence.

Triplet-State Structures, Energies, and Antiaromaticity of BN Analogues of Benzene and Their Benzo-Fused Derivatives

It is well known that benzene is aromatic in the ground state (the Hückel's rule) and antiaromatic in the first triplet (T₁) excited state (the Baird's rule). Whereas its BN analogues, the three isomeric dihydro-azaborines, have been shown to have various degrees of aromaticity in their ground state, almost no data are available for their T₁ states. Thus, the purpose of this work is to theoretically [B3LYP/6-311+G(d,p)] predict structures, energies, and antiaromaticity of T₁ dihydro-azaborines and some benzo-fused derivatives. Conclusions are based on spin density analysis, isogyric and hydrogenation reactions, HOMA, NICS, and ACID calculations. The results suggest that singlet-triplet energy gaps, antiaromaticity, and related excited-state properties of benzene, naphthalene, and anthracene could be tuned and controlled by the BN substitution pattern. While all studied compounds remain (nearly) planar upon excitation, the spin density distribution in T₁ 1,4-dihydro-azaborine induces a conformational change by which the two co-planar C-H bonds in the ground state become perpendicular to each other in the excited state. This predicted change in geometry could be of interest for the design of new photomechanical materials. Excitation of B-CN/N-NH₂ 1,4-azaborine would have a few effects: intramolecular charge transfer, aromaticity reversal, rotation, and stereoelectronic Umpolung of the amino group.

The influence of π-conjugation on competitive pathways: charge transfer or electron transfer in new D–π–A and D–π–Si–π–A dyads

Intramolecular charge transfer results in a partial charge transfer species (D^δ+–π–A^δ−). The disconnection of π-conjugation between the donor and acceptor causes a unit-electron transfer to form D˙⁺–π–Si–π–A˙⁻ species.

The driving forces for twisted or planar intramolecular charge transfer

The driving forces for twisting or planarization of excited D–A (donor–acceptor)-type chromophore have been investigated.

Integration of the 1,2,3-triazole "click" motif as a potent signalling element in metal ion responsive fluorescent probes

In a systematic approach we synthesized a new series of fluorescent probes incorporating donor-acceptor (D-A) substituted 1,2,3-triazoles as conjugative π-linkers between the alkali metal ion receptor N-phenylaza-[18]crown-6 and different fluorophoric groups with different electron-acceptor properties (4-naphthalimide, meso-phenyl-BODIPY and 9-anthracene) and investigated their performance in organic and aqueous environments (physiological conditions). In the charge-transfer (CT) type probes 1, 2 and 7, the fluorescence is almost completely quenched by intramolecular CT (ICT) processes involving charge-separated states. In the presence of Na(+) and K(+) ICT is interrupted, which resulted in a lighting-up of the fluorescence in acetonitrile. Among the investigated fluoroionophores, compound 7, which contains a 9-anthracenyl moiety as the electron-accepting fluorophore, is the only probe which retains light-up features in water and works as a highly K(+)/Na(+)-selective probe under simulated physiological conditions. Virtually decoupled BODIPY-based 6 and photoinduced electron transfer (PET) type probes 3-5, where the 10-substituted anthracen-9-yl fluorophores are connected to the 1,2,3-triazole through a methylene spacer, show strong ion-induced fluorescence enhancement in acetonitrile, but not under physiological conditions. Electrochemical studies and theoretical calculations were used to assess and support the underlying mechanisms for the new ICT and PET 1,2,3-triazole fluoroionophores.

Design, synthesis, insecticidal activity and structure-activity relationship of 3,3-dichloro-2-propenyloxy-containing phthalic acid diamide structures

BACKGROUND

Phthalic acid diamide derivatives are among the most important classes of synthetic insecticides. In this study, a 3,3-dichloro-2-propenyloxy group, the essential active group of pyridalyl derivatives, was incorporated into phthalic acid diamide derivatives with the aim of combining the active groups to generate more potent insecticides.

RESULTS

Thirty-one new phthalic acid diamides were obtained, and these were characterised by (1) H and (13) C NMR. The structure of N(2) -[1,1-dimethyl-2-(methoxy)ethyl]-3-iodo-N(1) -[4-(3,3-dichloro-2-propenyloxy)-3-(trifluoromethyl)phenyl]-1,2-benzenedicarboxamide was determined by X-ray diffraction crystallography. The insecticidal activities of the compounds against Plutella xylostella were evaluated. The title compounds exhibited excellent larvicidal activities against P. xylostella. Structure-activity relationships revealed that varying the combination of aliphatic amide and aromatic amide moieties, or the nature and position of substituent Y on the aniline ring, could aid the design of structures with superior performance.

CONCLUSION

A series of novel phthalic acid diamides containing a 3,3-dichloro-2-propenyloxy group at the 4-position of the aniline ring were designed and synthesised. Structure-activity relationships with the parent structure provided information that could direct further investigation on structure modification.

Synthesis, insecticidal activity, and structure-activity relationship of trifluoromethyl-containing phthalic acid diamide structures

Phthalic acid diamides have received considerable interest in agricultural chemistry due to a novel action mode, extremely high activity against a broad spectrum of lepidopterous insects, low acute toxicity to mammals, and environmentally benign characteristics. A series of phthalic acid diamides (4I-4IV) with the CF3 group at meta position on the aniline ring were synthesized. Their structures were characterized by (1)H NMR and (13)C NMR (or elemental analysis). The structure of N(2)-[1,1-dimethyl-2-(methylthio)ethyl]-3-iodo-N(1)-[3-fluoro-5-(trifluoromethyl)phenyl]-1,2-benzenedicarboxamide (4If) was determined by X-ray diffraction crystallography. Their insecticidal activities against Plutella xylostella were evaluated. The results show that some of the title compounds exhibit excellent larvicidal activities against P. xylostella, and improvement in larvicidal activity requires a reasonable combination of substituents in the parent structure, which provides some hints for further investigation on structure modification.

Intramolecular charge transfer processes in donor–acceptor substituted vinyltetrahydropyrenes

Two novel donor-acceptor-substituted vinyltetrahydropyrene derivatives, 2-N,N-dimethylamino-7-(1-carbethoxyvinyl)-4,5,9,10-tetrahydropyrene, , and 2-N,N-dimethylamino-7-(1,1-dicyanovinyl)-4,5,9,10-tetrahydropyrene, , were synthesized and their photophysical properties investigated in solvents of different polarities. Our studies revealed the existence of intramolecular charge transfer excited states in these molecules. For both compounds the fluorescence maxima exhibited solvent polarity-dependent red shifts. These were quantitatively analysed by the Lippert-Mataga and Liptay equations to obtain the excited state dipole moments. Our results indicated that in the case of , emission takes place from a planar (1)CT state in all non-protic solvents. In the case of , the nature of the excited state depends on the solvent. A fast relaxation to a triplet state is proposed in cyclohexane. The emitting state in medium polar solvents is a planar (1)CT state. In highly polar solvents a twisted (1)CT state is invoked to explain the low fluorescence quantum yield. For both compounds CT nature of the emitting states were further confirmed by studies in acidic medium. The ground and excited state pK(a) values for and were determined using absorption and emission spectral changes observed in the presence of protic acids.

Synthesis of twist-twist pi-conjugated di-sec-alkylstilbenes and stilbene polymers

Twist-twist pi-conjugated (TTPC) pi systems promise unique properties with their 90 degrees twist angles. Di-sec-alkyl substituted stilbenes, 5, were prepared by low-valent titanium coupling of phenyl ketones, 4. Long alkyl chains stopped the coupling reaction. Stilbenes 5 were shown to be approximately 90% TTPC. Inserting TTPC units into poly(p-phenylene) polymers created highly fluorescent, soluble, TTPC pi systems with weak electronic segmentation for organic light emitting diode (OLED) studies.

Photoredox, photodecarboxylation, and photo-retro-aldol chemistry of p-nitrobiphenyls

The photochemistry of three p-nitrobiphenyl derivatives 9-11 has been investigated to explore the ability of photoexcited nitro groups to induce chemistry through the biphenyl ring system. Previous work has shown that the nitro group is highly electron withdrawing at both the meta and para positions (on the benzene ring) in the excited triplet state, inducing decarboxylations and retro-Aldol type reactions, as well as a novel intramolecular redox-type reaction. The mechanisms of all of these reactions are believed to involve photogenerated nitrobenzyl carbanion-type intermediates. Analogous reactions with enhanced quantum efficiencies were observed in the nitrobiphenyls studied in this work. This is further evidence that twisted ground state biaryls (and possibly higher order oligophenylenes) may be thought of as highly polarizable electronically conjugated pi-systems in the excited state with the ability to induce efficient photochemistry. Moreover, a charge transfer triplet state is believed to be responsible for inducing highly efficient, novel acid-catalyzed pathways observed for the photodecarboxylation of 11 and the photoredox reaction of 9, neither of which has been observed in the corresponding nitrophenyl (parent) system.