Fluorene Analogues Research Articles

Fluorene analogues of xanthenes - low molecular weight near-infrared dyes.

Fluorene-based analogues of fluorescein, rhodol, and rhodamine exhibit absorption and fluorescence beyond 800-900 nm in water, 300-400 nm red-shifted compared to the original oxygen-bridged xanthene dyes, giving potential access to low molecular weight fluorescent markers for the second biological window (NIR-II, ca. 1000-1350 nm).

Synthesis and studies on the photophysical/biophysical properties of triazolylfluorene-labeled 2′-deoxyuridines

The planar structure, attractive photophysical property, and scarcity of electronically conjugated fluorene-containing biomolecular building blocks have attracted recent research interest on synthesizing triazolylfluorene decorated nucleosides with modulated photophysical features. Herein, we report the synthesis of few fluorescent nucleosides wherein the C5 of 2′-deoxyuridine is electronically conjugated with fluorene analogues via Sonogashira cross-coupling and copper-catalyzed click reaction. The study of photophysical properties of the synthesized nucleosides shows that two of the synthesized nucleosides show interesting dual emission properties in various organic solvents. The dual emitting fluorene nucleosides might impact significantly in nucleic acid research for monitoring the DNA microenvironment. Furthermore, we evaluated the interaction of cyanofluorenyl 2′-deoxyuridine with Calf thymus DNA (ctDNA) and observed that this nucleoside could sense ctDNA via the generation of an enhanced fluorescence signal.

Effect of controlling the number of fused rings on polymer photocatalysts for visible-light-driven hydrogen evolution

The introduction of fused thiophene units into the fluorene analogues, for the first time, resulted in an improved photocatalytic performance of the polymer photocatalysts.

Photocatalytic Hydrogen Evolution from Water Using Fluorene and Dibenzothiophene Sulfone-Conjugated Microporous and Linear Polymers

Three series of conjugated microporous polymers (CMPs) were studied as photocatalysts for hydrogen production from water using a sacrificial hole scavenger. In all cases, dibenzo[b,d]thiophene sulfone polymers outperformed their fluorene analogues. A porous network, S-CMP3, showed the highest hydrogen evolution rates of 6076 μmol h–1 g–1 (λ > 295 nm) and 3106 μmol h–1 g–1 (λ > 420 nm), with an external quantum efficiency of 13.2% at 420 nm. S-CMP3 outperforms its linear structural analogue, P35, whereas in other cases, nonporous linear polymers are superior to equivalent porous networks. This suggests that microporosity might be beneficial for sacrificial photocatalytic hydrogen evolution, if suitable linkers are used that do not limit charge transport and the material can be wetted by water as studied here by water sorption and quasi-elastic neutron scattering.

Synthesis and Characterization of Two Unsymmetrical Indenofluorene Analogues: Benzo[5,6]-s-indaceno[1,2-b]thiophene and Benzo[5,6]-s-indaceno[2,1-b]thiophene

The synthesis and characterization of two benzo-indaceno-thiophene compounds (anti-BIT and syn-BIT) are described. Two sequential Suzuki cross-couplings utilizing the halogen selectivity of this reaction permit modular assembly of unsymmetrical indeno[1,2-b]fluorene analogues. Analysis of their cyclic voltammetry and UV-vis spectra reveal that the optical and electrochemical properties of the BITs lie between those of indeno[1,2-b]fluorenes and indacenodithiophene.

ChemInform Abstract: Cu(I)‐Catalyzed Intramolecular Cyclizations of Substituted 2‐Iodobenzophenones under Thermal and Microwave Conditions.

Abstract Novel, easy-to-perform and practical intramolecular Cu(I)-catalyzed cyclizations of substituted 2-iodobenzophenones under thermal and microwave conditions are reported. The isolated cyclized products under microwave conditions are obtained with high yields and with short reaction times offering a valuable and reliable alternative to other protocols for the synthesis of fluorene analogues.

Cu(I)-catalyzed intramolecular cyclizations of substituted 2-iodobenzophenones under thermal and microwave conditions

Novel, easy-to-perform and practical intramolecular Cu(I)-catalyzed cyclizations of substituted 2-iodobenzophenones under thermal and microwave conditions are reported. The isolated cyclized products under microwave conditions are obtained with high yields and with short reaction times offering a valuable and reliable alternative to other protocols for the synthesis of fluorene analogues.

Intramolecular charge transfer, solvatochromism and hyperpolarizability of compounds bearing ethenylene or ethynylene bridges

Emission or both absorption/emission solvatochromic effects induced by intramolecular charge transfer (ICT) have been used to determine the excited-state dipole moments of the locally excited μe(LE) and the polar-solvent induced μe(ICT) states and the first hyperpolarizability parameter βCT of six asymmetric distyrylbenzene analogues, two 9,10-(diarylethynyl)anthracene derivatives and two 2,7-(diarylethynyl)fluorene analogues. The change in dipole moment under excitation (Δμeg) was also evaluated by theoretical calculations and compared with experimental data. All compounds display more or less remarkable positive solvatochromism which leads to relatively high hyperpolarizabilities and makes them interesting candidates for applications associated with photoinduced ICT. The structural effect on the transfer is also briefly discussed and related to the relaxation properties (previously investigated) of these compounds.

Quantum mechanical modelling and calculation of two-photon absorption properties of new class ‘Λ’-shaped conjugated molecules

Organic material with high intensity of two-photon absorption (TPA)-induced fluorescence can be used as the up-converter material for photovoltaic devices. In this work, quantum mechanics modelling techniques were applied to theoretically investigate one- and two-photon absorption properties of new ‘Λ’-shaped conjugated molecules. Fluorene and diphenylmethylene analogues as the π centres were chosen for building the π-conjugated bridges to connect the two types of strong electron donors, N,N-diphenylamino and carbazole groups. In these molecular structures, cyano and ketone groups were also selected to modify the π centres as electron acceptors. The TPA cross sections of these derivatives were calculated using two-state, three-state and sum-over-state models, respectively. Geometrical structures of these molecules were optimised using Hartree–Fock theory, and properties of excited states of these molecules were obtained based on configuration interaction with single excitations method. The effects of donor, acceptor and π centre on the TPA behaviours of these designed molecules were investigated. Several of these molecules have attractive TPA properties, which may have potential for photovoltaic device applications.

Carbazole nematic liquid crystals

A number of calamitic 2,7-diary-N-alkyl-substituted carbazoles with an enantiotropic nematic phase have been prepared. Branching of the aliphatic chain attached to the nitrogen atom in the carbazole ring leads to significantly lower liquid crystal transition temperatures. These new materials show a lower ionisation potential than fluorene analogues and blue photoluminescence in solution and as thin solid films.

A QM/QM Multilayer Composite Methodology: The ONIOM Correlation Consistent Composite Approach (ONIOM-ccCA)

A QM/QM approach incorporating the correlation consistent composite approach (ccCA) into the ONIOM multilayer methodology has been implemented. This new multilayer composite scheme, ONIOM-ccCA, enables the accurate prediction of thermochemical properties for systems containing dozens-and potentially hundreds-of atoms. ONIOM-ccCA is used to predict the C-H bond dissociation energies of 18 anthracene and fluorene analogues, containing up to 43 atoms, to within 1.2 kcal mol(-1) of experimental values. Several density functional and basis set combinations are evaluated for use as the low level QM layer. The mean absolute deviation (1.2 kcal mol(-1)) using the most accurate ONIOM-ccCA method, ccCA:B3LYP/cc-pVTZ, is significantly lower than that of an earlier reported multilayer composite scheme [2.4 kcal mol(-1), Li, M.-J.; Liu, L.; Fu, Y.; Guo, Q.-X. J. Phys. Chem. B, 2005, 109, 13818]. Thus, through use of ONIOM-ccCA, accurate thermochemical calculations are now feasible for sizable molecular systems of chemical or biological interest.

Improved, Selective, Human Intestinal Carboxylesterase Inhibitors Designed to Modulate 7-Ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin (Irinotecan; CPT-11) Toxicity

CPT-11 is an antitumor prodrug that is hydrolyzed by carboxylesterases (CE) to yield SN-38, a potent topoisomerase I poison. However, the dose limiting toxicity delays diarrhea that is thought to arise, in part, from activation of the prodrug by a human intestinal CE (hiCE). Therefore, we have sought to identify selective inhibitors of hiCE that may have utility in modulating drug toxicity. We have evaluated one such class of molecules (benzene sulfonamides) and developed QSAR models for inhibition of this protein. Using these predictive models, we have synthesized a panel of fluorene analogues that are selective for hiCE, demonstrating no cross reactivity to the human liver CE, hCE1, or toward human cholinesterases, and have K(i) values as low as 14 nM. These compounds prevented hiCE-mediated hydrolysis of the drug and the potency of enzyme inhibition correlated with the clogP of the molecules. These studies will allow the development and application of hiCE-specific inhibitors designed to selectively modulate drug hydrolysis in vivo.

The effect of the heteroatom on the radiative deactivation of the lowest triplet state in heterocyclic analogues of fluorene

The vibronic transition strengths F VSO s for the transitions from the spin sublevels s of the triplet state T 1 to the energy levels of the nontotally symmetric vibrations of dibenzothiophene (DB(S)) are calculated. For a series of heterocyclic analogues of fluorene (DB(S) and previously studied carbazole, dibenzofuran, and phenyldibenzophosphole), the regular features of the effect of the valence state of the heteroatom and of the spin-orbit interactions in individual atomic groups of the molecule are revealed. The factors affecting changes in the radiative deactivation rate constant of the T 1 state of the molecules studied are established. The intensity distribution of the vibronic lines in the Herzberg-Teller component of the fine structure phosphorescence spectrum of phenyldibenzophosphole is calculated taking into account different populations of the triplet sublevels.

Vibronic-spin-orbit interactions in heterocyclic analogues of fluorene with the N and O heteroatoms

The transition dipole moments P 0 s for the transitions from the electronic triplet state 3 B 2(ππ*) to vibrational sublevels of the vibrational out-of-plane modes n of the carbazole and dibenzofuran molecules are calculated. The values of the radiative deactivation rate constant k rad s of the triplet sublevels T s are determined along with the components k SO s and k VSO s of this constant, which depend on the intramolecular spin-orbit (SO) and vibronic-spin-orbit (VSO) interaction. It is ascertained that k rad z > k rad y . For different structural units of the molecules (the heteroatom and the carbon atoms of the dibenzene fragment), the effect of the SO coupling on the constant k VSO∼Σs, n (P 0 s )2 is studied. A competition between the effects on k VSO from the SO coupling in the carbon atoms and in the light N and O heteroatoms is revealed. This competition accounts for the weak influence of the heteroatom on this component of the rate constant k rad in these molecules. It is ascertained that the intensity distribution among the vibronic lines in the phosphorescence spectra of carbazole and dibenzofuran I 0n ∼Σs (P 0 s )2 is different due to the substantially different influence of the N and O heteroatoms on the deactivation of the triplet sublevel T y .

The effect of the nonplanarity of heterocyclic analogues of fluorene with the phosphorus atom on spin-orbit interactions

The transition dipole moments P00S for the transitions from the sublevels s=z,y, and x of the triplet electronic states 3A″, which are caused by intramolecular spin-orbit (SO) interactions, are calculated. The calculation is carried out for molecules of heterocyclic analogues of fluorene containing phosphorus and nitrogen (namely, the groups P-H, P-C6H5, and N-H). The influence that the planar and nonplanar models of the molecules, as well as the substituents −C6H5 and −H at the heteroatom (HA), exert on the values of (P00S)2 and on the directions of the corresponding vectors is considered. The values of the component \(k_{SO^ \sim } \sum _s (P_{00}^s )^2 \) of the radiative deactivation rate constant of the T1 state are calculated. It is ascertained that, in the series of molecules with HA = N, O, P, and S, both the calculated values of kSO and those experimentally determined from an analysis of the intensity distribution in fine-structure phosphorescence spectra vary little, whereas the constant of the SO coupling in the heteroatom ςHA increases substantially along this series. The reason for the weak influence of ςHA on values of kSO—common for both planar and nonplanar molecules—is found.

Transition Metal Complexes with Heterocyclic Analogues of Fluorene. Part 1. Synthesis, Structures, and Haptotropic Rearrangements of Tricarbonylchromium Complexes of Dibenzothiophene.

Transition Metal Complexes with Heterocyclic Analogues of Fluorene. Part 1. Synthesis, Structures, and Haptotropic Rearrangements of Tricarbonylchromium Complexes of Dibenzothiophene.

Spin-orbit interactions in heterocyclic analogues of fluorene

For carbazole, dibenzofuran, and dibenzothiophene—heterocyclic analogues of fluorene containing N-H, O, and S groups, respectively—the transition dipole moments P 00 i for the transitions 3 B 2→S 0 and 3 A 1→S 0 from the sublevels i=z, y, x of the triplet electronic ππ* states, which are caused by intramolecular spin-orbit (SO) interactions, are calculated. The effect that the SO coupling between the S 0 state and highest triplet states has on the calculation results is considered. The effects exerted on the value of P 00 i by such specific features of the molecular structure as the position of a heteroatom on the symmetry axis, its valence, and different constants of SO coupling in heteroatoms are discussed. The reason for the weak influence of the quantity ςHA on the rate constant of radiative deactivation of the lowest T state is ascertained.

Toxicity of eight polycyclic aromatic compounds to red clover ( Trifolium pratense), ryegrass ( Lolium perenne), and mustard ( Sinapsis alba)

The effect of eight polycyclic aromatic compounds (PACs) on the seed emergence and early life-stage growth of three terrestrial plants ( Sinapsis alba, Trifolium pratense and Lolium perenne) were studied in a greenhouse, using a Danish agricultural soil with an organic carbon content of 1.6%. After three weeks of exposure, seed emergence and seedling weight (fresh weight and dry weight) were determined. Exposure concentrations were verified with chemical analysis. The substances tested were four polycyclic aromatic hydrocarbons (fluoranthene, pyrene, phenanthrene and fluorene), the N-, S-, and O-substituted analogues of fluorene (carbazole, dibenzothiophene and dibenzofuran, respectively), and the quinoline representative acridine. Seedling growth was a far more sensitive endpoint than seed emergence for all substances. Concentrations estimated to give a 20% reduction of seedling fresh weight (EC20-values) ranged from 36 to 290 mg kg −1 for carbazole, 43 to 93 mg kg −1 for dibenzofuran, 37 to 110 mg kg −1 for dibenzothiophene, 140 to 650 mg kg −1 for fluoranthene, 55 to 380 mg kg −1 for fluorene, 37 to 300 mg kg −1 for phenanthrene, and 49 to 1300 mg kg −1 for pyrene. For acridine, no toxicity was observed within the concentration range tested (1–1000 mg kg −1). As illustrated by the EC20-values, there was a rather large difference in sensitivity between the species, and T. pratense was the most sensitive of the species tested.

Bacterial degradation of aromatic compounds via angular dioxygenation.

Dioxygenation is one of the important initial reactions of the bacterial degradation of various aromatic compounds. Aromatic compounds, such as biphenyl, toluene, and naphthalene, are dioxygenated at lateral positions of the aromatic ring resulting in the formation of cis-dihydrodiol. This "normal" type of dioxygenation is termed lateral dioxygenation. On the other hand, the analysis of the bacterial degradation of fluorene (FN) analogues, such as 9-fluorenone, dibenzofuran (DF), carbazole (CAR), and dibenzothiophene (DBT)-sulfone, and DF-related diaryl ether compounds, dibenzo-p-dioxin (DD) and diphenyl ether (DE), revealed the presence of the novel mode of dioxygenation reaction for aromatic nucleus, generally termed angular dioxygenation. In this atypical dioxygenation, the carbon bonded to the carbonyl group in 9-fluorenone or to heteroatoms in the other compounds, and the adjacent carbon in the aromatic ring are both oxidized. Angular dioxygenation of DF, CAR, DBT-sulfone, DD, and DE produces the chemically unstable hemiacetal-like intermediates, which are spontaneously converted to 2,2',3-trihydroxybiphenyl, 2'-aminobiphenyl-2,3-diol, 2',3'-dihydroxybiphenyl-2-sulfinate, 2,2',3-trihydroxydiphenyl ether, and phenol and catechol, respectively. Thus, angular dioxygenation for these compounds results in the cleavage of the three-ring structure or DE structure. The angular dioxygenation product of 9-fluorenone, 1-hydro-1,1a-dihydroxy-9-fluorenone is a chemically stable cis-diol, and is enzymatically transformed to 2'-carboxy-2,3-dihydroxybiphenyl. 2'-Substituted 2,3-dihydroxybiphenyls formed by angular dioxygenation of FN analogues are degraded to monocyclic aromatic compounds by meta cleavage and hydrolysis. Thus, after the novel angular dioxygenation, subsequent degradation pathways are homologous to the corresponding part of that of biphenyl. Compared to the bacterial strains capable of catalyzing lateral dioxygenation, few bacteria having angular dioxygenase have been reported. Only a few degradation pathways, CAR-degradation pathway of Pseudomonas resinovorans strain CA10, DF/DD-degradation pathway of Sphingomonas wittichii strain RW1, DF/DD/FN-degradation pathway of Terrabacter sp. strain DBF63, and carboxylated DE-degradation pathway of P. pseudoalcaligenes strain POB310, have been investigated at the gene level. As a result of the phylogenetic analysis and the comparison of substrate specificity of angular dioxygenase, it is suggested that this atypical mode of dioxygenation is one of the oxygenation reactions originating from the relaxed substrate specificity of the Rieske nonheme iron oxygenase superfamily. Genetic characterization of the degradation pathways of these compounds suggests the possibility that the respective genetic elements constituting the entire catabolic pathway have been recruited from various other bacteria and/or other genetic loci, and that these pathways have not evolutionary matured.

Synthesis of new two-photon absorbing fluorene derivatives via Cu-mediated Ullmann condensations

The Ullmann amination reaction was utilized to provide access to a number of fluorene analogues from common intermediates, via facile functionalization at positions 2, 7, and 9 of the fluorene ring. Through variation of amine or iodofluorene derivative, analogues bearing substitutents with varying electron-donating and electron-withdrawing ability, e.g., diphenylamino, bis-(4-methoxyphenyl)amine, nitro, and benzothiazole, were synthesized in good yield. The novel fluorene derivatives were fully characterized, including absorption and emission spectra. Didecylation at the 9-position afforded remarkably soluble derivatives. Target compounds 4, 5, and 9 are potentially useful as fluorophores in two-photon fluorescence microscopy. Their UV-vis spectra display desirable absorption in the range of interest suitable for two-photon excitation by near-IR femtosecond lasers. Preliminary measurements of two-photon absorption indicate the derivatives exhibit high two-photon absorptivity, affirming their potential as two-photon fluorophores. For example, using a 1,210 nm femtosecond pump beam, diphenylaminobenzothiazolylfluorene 4 exhibited nondegenerate two-photon absorption, with two-photon absorptivity (delta) of ca. 820 x 10(-50) cm(4) s photon(-1) molecule(-1) at the femtosecond white light continuum probe wavelength of 615 nm.