New pyridine-based chalcones and pyrazolines with anticancer, antibacterial, and antiplasmodial activities.

New pyridine-based chalcones 4a-h and pyrazolines 5a-h (N-acetyl), 6a-h (N-phenyl), and 7a-h (N-4-chlorophenyl) were synthesized and evaluated by the National Cancer Institute (NCI) against 60 different human cancer cell lines. Pyrazolines 6a, 6c-h, and 7a-h satisfied the pre-determined threshold inhibition criteria, obtaining that compounds 6c and 6f exhibited high antiproliferative activity, reaching submicromolar GI50 values from 0.38 to 0.45 µM, respectively. Moreover, compound 7g (4-CH3) exhibited the highest cytostatic activity of these series against different cancer cell lines from leukemia, nonsmall cell lung, colon, ovarian, renal, and prostate cancer, with LC50 values ranging from 5.41 to 8.35 µM, showing better cytotoxic activity than doxorubicin. Furthermore, the compounds were tested for antibacterial and antiplasmodial activities. Chalcone 4c was the most active with minimal inhibitory concentration (MIC) = 2 µg/mL against methicillin-resistant Staphylococcus aureus (MRSA), while the pyrazoline 6h showed a MIC = 8 µg/mL against Neisseria gonorrhoeae. For anti-Plasmodium falciparum activity, the chalcones display higher activity with EC50 values ranging from 10.26 to 10.94 µg/mL. Docking studies were conducted against relevant proteins from P. falciparum, exhibiting the minimum binding energy with plasmepsin II. In vivo toxicity assay in Galleria mellonella suggests that most compounds are low or nontoxic.

Synthesis of Novel Triazine-Based Chalcones and 8,9-dihydro-7H-pyrimido[4,5-b][1,4]diazepines as Potential Leads in the Search of Anticancer, Antibacterial and Antifungal Agents.

This study presents the synthesis of four series of novel hybrid chalcones (20,21)a-g and (23,24)a-g and six series of 1,3,5-triazine-based pyrimido[4,5-b][1,4]diazepines (28-33)a-g and the evaluation of their anticancer, antibacterial, antifungal, and cytotoxic properties. Chalcones 20b,d, 21a,b,d, 23a,d-g, 24a-g and the pyrimido[4,5-b][1,4]diazepines 29e,g, 30g, 31a,b,e-g, 33a,b,e-g exhibited outstanding anticancer activity against a panel of 60 cancer cell lines with GI50 values between 0.01 and 100 µM and LC50 values in the range of 4.09 µM to >100 µM, several of such derivatives showing higher activity than the standard drug 5-fluorouracil (5-FU). On the other hand, among the synthesized compounds, the best antibacterial properties against N. gonorrhoeae, S. aureus (ATCC 43300), and M. tuberculosis were exhibited by the pyrimido[4,5-b][1,4]diazepines (MICs: 0.25-62.5 µg/mL). The antifungal activity studies showed that triazinylamino-chalcone 29e and triazinyloxy-chalcone 31g were the most active compounds against T. rubrum and T. mentagrophytes and A. fumigatus, respectively (MICs = 62.5 µg/mL). Hemolytic activity studies and in silico toxicity analysis demonstrated that most of the compounds are safe.

In silico prediction and in vitro assessment of novel heterocyclics with antimalarial activity.

The development of new antimalarials is paramount to keep the goals on reduction of malaria cases in endemic regions. The search for quality hits has been challenging as many inhibitory molecules may not progress to the next development stage. The aim of this work was to screen an in-house library of heterocyclic compounds (HCUV) for antimalarial activity combining computational predictions and phenotypic techniques to find quality hits. The physicochemical determinants, pharmacokinetic properties (ADME), and drug-likeness of HCUV were evaluated in silico, and compounds were selected for structure-based virtual screening and in vitro analysis. Seven Plasmodium target proteins were selected from the DrugBank Database, and ligands and receptors were processed using UCSF Chimera and Open Babel before being subjected to docking using Autodock Vina and Autodock 4. Growth inhibition of P. falciparum (3D7) cultures was tested by SYBR Green assays, and toxicity was assessed using hemolytic activity tests and the Galleria mellonella in vivo model. From a total of 792 compounds, 341 with good ADME properties, drug-likeness, and no interference structures were subjected to in vitro analysis. Eight compounds showed IC50 ranging from 0.175 to 0.990 µM, and active compounds included pyridyl-diaminopyrimido-diazepines, pyridyl-N-acetyl- and pyridyl-N-phenyl-pyrazoline derivatives. The most potent compound (UV802, IC50 0.178 µM) showed no toxicophoric and was predicted to interact with P. falciparum 1-cysperoxidredoxin (PfPrx1). For the remaining 7 hits (IC50 < 1 µM), 3 showed in silico binding to PfPrx1, one was predicted to bind the haloacid dehalogenase-like hydrolase and plasmepsin II, and one interacted with the plasmodial heat shock protein 90.

Synthesis, Anticancer and Antitubercular Properties of New Chalcones and Their Nitrogen-Containing Five-Membered Heterocyclic Hybrids Bearing Sulfonamide Moiety.

A new series of sulfonamides, 8a-b, 10, 12, and 14a-b, were synthesized by N-sulfonation reaction with sulfonyl chlorides 6a-b. Five new series of chalcone-sulfonamide hybrids (16-20)a-f were prepared via Claisen-Schmidt condensation of the newly obtained sulfonamides with aromatic aldehydes 15a-f in basic medium. Chalcones substituted with chlorine at position 4 of each series were used as precursors for the generation of their five-membered heterocyclic pyrazoline (22-23)a-d, (24-25)a-b and carbothioamide 27a-f derivatives. The synthesized compounds were evaluated for their anticancer and antituberculosis activities. To determine their anticancer activity, compounds were screened against sixty human cancer cell lines at a single dose (10 µM). Compounds 17a-c were highly active against LOX IMVI (melanoma), with IC50 values of 0.34, 0.73 and 0.54 µM, respectively. Chalcone 18e showed remarkable results against the entire panel of leukemia cell lines with IC50 values between 0.99-2.52 µM. Moreover, compounds 20e and 20f displayed growth inhibition of Mycobacterium tuberculosis H37Rv at concentrations below 10 µM. Although they showed low selectivity in cytotoxicity tests against the Vero cell line, further optimization could advance the potential biological activity of the selected compounds.

Triazine: An Important Building Block of Organic Materials for Solar Cell Application.

Since the beginning of the 21st century, triazine-based molecules have been employed to construct different organic materials due to their unique optoelectronic properties. Among their applications, photovoltaics stands out because of the current need to develop efficient, economic, and green alternatives to energy generation based mainly on fossil fuels. Here, we review all the development of triazine-based organic materials for solar cell applications, including organic solar cells, dye-sensitized solar cells, and perovskite solar cells. Firstly, we attempt to illustrate the main synthetic routes to prepare triazine derivatives. Then, we introduce the main aspects associated with solar cells and their performance. Afterward, we discuss different works focused on the preparation, characterization, and evaluation of triazine derivatives in solar cells, distinguishing the type of photovoltaics and the role of the triazine-based material in their performance (e.g., as a donor, acceptor, hole-transporting material, electron-transporting material, among others). Throughout this review, the progress, drawbacks, and main issues of the performance of the mentioned solar cells are exposed and discussed. Finally, some conclusions and perspectives about this research topic are mentioned.

Design, synthesis, and molecular docking study of novel quinoline-based bis-chalcones as potential antitumor agents.

A novel series of quinoline-based symmetrical and unsymmetrical bis-chalcones was synthesized via a Claisen-Schmidt condensation reaction between 3-formyl-quinoline/quinolone derivatives with acetone or arylidene acetones, respectively, by using KOH/MeOH/H2 O as a reaction medium. Twelve of the obtained compounds were evaluated for their in vitro cytotoxic activity against 60 different human cancer cell lines according to the National Cancer Institute protocol. Among the screened compounds, the symmetrical N-butyl bis-quinolinyl-chalcone 14g and the unsymmetrical quinolinyl-bis-chalcone 17o bearing a 7-chloro-substitution on the N-benzylquinoline moiety and 4-hydroxy-3-methoxy substituent on the phenyl ring, respectively, exhibited the highest overall cytotoxicity against the evaluated cell lines with a GI50 range of 0.16-5.45 µM, with HCT-116 (GI50 = 0.16) and HT29 (GI50 = 0.42 µM) (colon cancer) representing best-case scenarios. Notably, several GI50 values for these compounds were lower than those of the reference drugs doxorubicin and 5-FU. Docking studies performed on selected derivatives yielded very good binding energies in the active site of proteins that participate in key carcinogenic pathways.

5-(Indol-2-yl)pyrazolo[3,4-b]pyridines as a New Family of TASK-3 Channel Blockers: A Pharmacophore-Based Regioselective Synthesis.

TASK channels belong to the two-pore-domain potassium (K2P) channels subfamily. These channels modulate cellular excitability, input resistance, and response to synaptic stimulation. TASK-channel inhibition led to membrane depolarization. TASK-3 is expressed in different cancer cell types and neurons. Thus, the discovery of novel TASK-3 inhibitors makes these bioactive compounds very appealing to explore new cancer and neurological therapies. TASK-3 channel blockers are very limited to date, and only a few heterofused compounds have been reported in the literature. In this article, we combined a pharmacophore hypothesis with molecular docking to address for the first time the rational design, synthesis, and evaluation of 5-(indol-2-yl)pyrazolo[3,4-b]pyridines as a novel family of human TASK-3 channel blockers. Representative compounds of the synthesized library were assessed against TASK-3 using Fluorometric imaging plate reader-Membrane Potential assay (FMP). Inhibitory properties were validated using two-electrode voltage-clamp (TEVC) methods. We identified one active hit compound (MM-3b) with our systematic pipeline, exhibiting an IC50 ≈ 30 µM. Molecular docking models suggest that compound MM-3b binds to TASK-3 at the bottom of the selectivity filter in the central cavity, similar to other described TASK-3 blockers such as A1899 and PK-THPP. Our in silico and experimental studies provide a new tool to predict and design novel TASK-3 channel blockers.

Azatruxene-Based, Dumbbell-Shaped, Donor-π-Bridge-Donor Hole-Transporting Materials for Perovskite Solar Cells.

Three novel donor-π-bridge-donor (D-π-D) hole-transporting materials (HTMs) featuring triazatruxene electron-donating units bridged by different 3,4-ethylenedioxythiophene (EDOT) π-conjugated linkers have been synthesized, characterized, and implemented in mesoporous perovskite solar cells (PSCs). The optoelectronic properties of the new dumbbell-shaped derivatives (DTTXs) are highly influenced by the chemical structure of the EDOT-based linker. Red-shifted absorption and emission and a stronger donor ability were observed in passing from DTTX-1 to DTTX-2 due to the extended π-conjugation. DTTX-3 featured an intramolecular charge transfer between the external triazatruxene units and the azomethine-EDOT central scaffold, resulting in a more pronounced redshift. The three new derivatives have been tested in combination with the state-of-the-art triple-cation perovskite [(FAPbI3 )0.87 (MAPbBr3 )0.13 ]0.92 [CsPbI3 ]0.08 in standard mesoporous PSCs. Remarkable power conversion efficiencies of 17.48 % and 18.30 % were measured for DTTX-1 and DTTX-2, respectively, close to that measured for the benchmarking HTM spiro-OMeTAD (18.92 %), under 100 mA cm-2 AM 1.5G solar illumination. PSCs with DTTX-3 reached a PCE value of 12.68 %, which is attributed to the poorer film formation in comparison to DTTX-1 and DTTX-2. These PCE values are in perfect agreement with the conductivity and hole mobility values determined for the new compounds and spiro-OMeTAD. Steady-state photoluminescence further confirmed the potential of DTTX-1 and DTTX-2 for hole-transport applications as an alternative to spiro-OMeTAD.

New thiazolyl-pyrazoline derivatives bearing nitrogen mustard as potential antimicrobial and antiprotozoal agents.

A new series of N-substituted pyrazoline derivatives 6a-g, 7a-g, 8a-g, and 9a-g was synthetized by reaction of hydrazine derivatives and chalcone-thiazole hybrids bearing nitrogen mustard 5a-g. The chalcones 5a-g were obtained by Claisen-Schmidt condensation of thiazole-2-nitrogen mustard 3 and selected acetophenones 4a-g. These new compounds 6/7/8/9a-g were screened for their antifungal activity against Cryptococcus neoformans, with IC50 values of 3.9-7.8 µg/ml for the N-3,5-dichlorophenyl pyrazolines 9e-g. Interestingly, those compounds show low cytotoxic effects toward erythrocytes (RBC). In addition, N-acetyl (6a,b) and N-formyl pyrazolines (7a, 7b, 7c, and 7g) showed inhibitory activity against methicillin-susceptible Staphylococcus aureus, methicillin-resistant S. aureus, and vancomycin-intermediate S. aureus, with the most important minimum inhibitory concentration values ranging from 31.25 to 125 µg/ml. Regarding the antiprotozoal activity, thiazolyl-pyrazolines 9g, 8f, and 7c display high activity against Plasmodium falciparum, Leishmania (V) panamensis, and Trypanosoma cruzi, with EC50 values of 11.80, 6.46, and 4.98 µM, respectively, and with 7c being approximately 2.6-fold more potent than benznidazole with a selectivity index of 1.61 on U-937 human cells, showing promising potential as a novel antitrypanosomal agent.

Design and Synthesis of New 6-Nitro and 6-Amino-3,3a,4,5-Tetrahydro-2H-Benzo[g]indazole Derivatives: Antiproliferative and Antibacterial Activity.

New substituted benzo[g]indazoles functionalized with a 6-nitro and 6-amino groups have been synthesized by the reaction of benzylidene tetralones with hydrazine in acetic acid. The resulting conformationally-constrained compounds were evaluated for their antiproliferative activity against selected cancer cell lines. The nitro-based indazoles 11a, 11b, 12a and 12b have shown IC50 values between 5-15 µM against the lung carcinoma cell line NCI-H460. Moreover, the nitro compounds were tested for antibacterial activity where compounds 12a and 13b have shown MIC values of 250 and 62.5 µg/mL against N. gonorrhoeae with no hemolytic activity in human red blood cells (RBC).

Catalyst-free assembly of giant tris(heteroaryl)methanes: synthesis of novel pharmacophoric triads and model sterically crowded tris(heteroaryl/aryl)methyl cation salts.

A series of giant tris(heteroaryl)methanes are easily assembled by one-pot three-component synthesis by simple reflux in ethanol without catalyst or additives. Diversely substituted indoles (Ar1) react with quinoline aldehydes, quinolone aldehydes, chromone aldehydes, and fluorene aldehydes (Ar2CHO) and coumarins (Ar3) in 1:1:1 ratio to form the corresponding tris(heteroaryl)methanes (Ar1Ar2Ar3)CH along with (Ar1Ar1Ar2)CH triads. A series of new 2:1 triads were also synthesized by coupling substituted indoles with Ar2CHO. The coupling reactions could also be carried out in water (at circa 80 °C) but with chemoselectivity favoring (Ar1Ar1Ar2)CH over (Ar1Ar2Ar3)CH. The molecular structure of a representative (Ar1Ar2Ar3)CH triad was confirmed by X-ray analysis. Model tris(heteroaryl/aryl)methylium salts were generated by reaction with DDQ/HPF6 and studied by NMR and by DFT and GIAO-DFT.

Synthesis of New 1,3,5-Triazine-Based 2-Pyrazolines as Potential Anticancer Agents.

A new series of 1,3,5-triazine-containing 2-pyrazoline derivatives (8⁻11)a⁻g was synthesized by cyclocondensation reactions of [(4,6-bis((2-hydroxyethyl)amino)-1,3,5-triazin-2-yl)amine]chalcones 7a⁻g with hydrazine hydrate and derivatives. Chalcones 7a⁻g were obtained by Claisen-Schmidt condensation between aromatic aldehydes and triazinic derivative 5, which was synthesized in high yield by a microwave-assisted reaction. Seventeen of the synthesized compounds were selected and tested by the US National Cancer Institute (NCI) for their anticancer activity against 58 different human tumor cell lines. Compounds 7g and 10d,e,g showed important GI50 values ranging from 0.569 to 16.6 µM and LC50 values ranging from 5.15 to >100 µM.

Design of Two Alternative Routes for the Synthesis of Naftifine and Analogues as Potential Antifungal Agents.

Two practical and efficient approaches have been implemented as alternative procedures for the synthesis of naftifine and novel diversely substituted analogues 16 and 20 in good to excellent yields, mediated by Mannich-type reactions as the key step of the processes. In these approaches, the γ-aminoalcohols 15 and 19 were obtained as the key intermediates and their subsequent dehydration catalyzed either by Brønsted acids like H2SO4 and HCl or Lewis acid like AlCl3, respectively, led to naftifine, along with the target allylamines 16 and 20. The antifungal assay results showed that intermediates 18 (bearing both a ß-aminoketo- and N-methyl functionalities in their structures) and products 20 were the most active. Particularly, structures 18b, 18c, and the allylamine 20c showed the lowest MIC values, in the 0.5-7.8 µg/mL range, against the dermatophytes Trichophyton rubrum and Trichophyton mentagrophytes. Interesting enough, compound 18b bearing a 4-Br as the substituent of the phenyl ring, also displayed high activity against Candida albicans and Cryptococcus neoformans with MIC80 = 7.8 µg/mL, being fungicide rather than fungistatic with a relevant MFC value = 15.6 µg/mL against C. neoformans.

In Silico and in Vitro-Guided Identification of Inhibitors of Alkylquinolone-Dependent Quorum Sensing in Pseudomonas aeruginosa.

Pseudomonas aeruginosa is a major opportunistic pathogen in cystic fibrosis, wound and nosocomial infections, posing a serious burden to public health, due to its antibiotic resistance. The P. aeruginosa Pseudomonas Quinolone System (pqs) quorum sensing system, driven by the activation of the transcriptional regulator, PqsR (MvfR) by alkylquinolone (AQ) signal molecules, is a key player in the regulation of virulence and a potential target for the development of novel antibacterial agents. In this study, we performed in silico docking analysis, coupled with screening using a P. aeruginosa mCTX::PpqsA-lux chromosomal promoter fusion, to identify a series of new PqsR antagonists. The hit compounds inhibited pyocyanin and alkylquinolone signal molecule production in P. aeruginosa PAO1-L and PA14 strains. The inhibitor Ia, which showed the highest activity in PA14, reduced biofilm formation in PAO1-L and PA14, increasing their sensitivity to tobramycin. Furthermore, the hepatic and plasma stabilities for these compounds were determined in both rat and human in vitro microsomal assays, to gain a further understanding of their therapeutic potential. This work has uncovered a new class of P. aeruginosa PqsR antagonists with potential for hit to lead optimisation in the search for quorum sensing inhibitors for future anti-infective drug discovery programs.

Synthesis of novel 7-aryl and 7-spiropyrazolo[4',3':5,6]pyrido[2,3-d]pyrimidine derivatives and their study as AChE inhibitors.

An efficient route for the synthesis of novel 7-aryl and 7-spiropyrazolo[4[Formula: see text],3[Formula: see text]:5,6]pyrido[2,3-d]pyrimidine derivatives is described. These compounds were obtained by a cyclocondensation reaction between pyrazolopyridinediamines 4 and aldehydes 5 or cyclic ketones 6 in the presence of acetic acid as catalyst. This procedure provides the desired compounds in good yields under a simple two-step methodology. The obtained compounds were evaluated as AChE inhibitors and showed weak AChe inhibition with [Formula: see text].

Synthesis and Antifungal in Vitro Evaluation of Pyrazolo[3,4-b]pyridines Derivatives Obtained by Aza-Diels-Alder Reaction and Microwave Irradiation.

A series of pyrazolo[3,4-b]pyridines were prepared by a microwave-assisted aza-Diels-Alder reaction between pyrazolylformimidamides 1 and ß-nitrostyrenes 2 in toluene as the solvent. This procedure provides a simple one-step and environmentally friendly methodology with good yields for the synthesis of these compounds. All compounds were tested for antifungal activity against two clinically important fungi Candida albicans and Cryptococcus neoformans. Within the compounds of the series bearing a -CH3 group on the carbon C-3 of the azole ring (3a-e), the compound without a substituent on the p'-phenyl ring (3a), showed the best activity against both fungi, followed by the p'-Br-phenyl (3c). Within the compounds of the series bearing a tert-butyl group in the carbon C-3 of the azole ring (3f-j), the non-substituted p'-compound (3f) was the most active one, followed by (3h) (p'-Br substituted) that showed the best activity against both fungi. The remaining compounds of this sub-series (3g, i, j) showed similar moderate activities. The antifungal activity of the compounds of the series was found to be correlated with a higher log P and a lower dipole moment in the more active compounds.

Synthesis and DFT Calculations of Novel Vanillin-Chalcones and Their 3-Aryl-5-(4-(2-(dimethylamino)-ethoxy)-3-methoxyphenyl)-4,5-dihydro-1H-pyrazole-1-carbaldehyde Derivatives as Antifungal Agents.

Novel (E)-1-(aryl)-3-(4-(2-(dimethylamino)ethoxy)-3-methoxyphenyl) prop-2-en-1-ones 4 were synthesized by a Claisen-Schmidt reaction of 4-(2-(dimethylamino)ethoxy)-3-methoxy-benzaldehyde (2) with several acetophenone derivatives 3. Subsequently, cyclocondensation reactions of chalcones 4 with hydrazine hydrate afforded the new racemic 3-aryl-5-(4-(2-(dimethylamino)ethoxy)-3-methoxyphenyl)-4,5-dihydro-1H-pyrazole-1-carbaldehydes 5 when the reaction was carried out in formic acid. The antifungal activity of both series of compounds against eight fungal species was determined. In general, chalcone derivatives 4 showed better activities than pyrazolines 5 against all tested fungi. None of the compounds 4a-g and 5a-g showed activity against the three Aspergillus spp. In contrast, most of the compounds 4 showed moderate to high activities against three dermatophytes (MICs 31.25-62.5 µg/mL), being 4a followed by 4c the most active structures. Interestingly, 4a and 4c possess fungicidal rather than fungistatic activities, with MFC values between 31.25 and 62.5 µg/mL. The comparison of the percentages of inhibition of C. neoformans by the most active compounds 4, allowed us to know the role played by the different substituents of the chalcones' A-ring. Also the most anti-cryptococcal compounds 4a-c and 4g, were tested in a second panel of five clinical C. neoformans strains in order to have an overview of their inhibition capacity not only of standardized but also of clinical C. neoformans strains. DFT calculations showed that the electrophilicity is the main electronic property to explain the differences in antifungal activities for the synthesized chalcones and pyrazolines compounds. Furthermore, a quantitative reactivity analysis showed that electron-withdrawing substituted chalcones presented the higher electrophilic character and hence, the greater antifungal activities among compounds of series 4.

Hybrid Molecules Containing a 7-Chloro-4-aminoquinoline Nucleus and a Substituted 2-Pyrazoline with Antiproliferative and Antifungal Activity.

Twenty-four new hybrid analogues (15-38) containing 7-chloro-4-aminoquinoline and 2-pyrazoline N-heterocyclic fragments were synthesized. Twelve of the new compounds were evaluated against 58 human cancer cell lines by the U.S. National Cancer Institute (NCI). Compounds 25, 30, 31, 36, and 37 showed significant cytostatic activity, with the most outstanding GI50 values ranging from 0.05 to 0.95 µM. The hybrid compounds (15-38) were also evaluated for antifungal activity against Candida albicans and Cryptococcus neoformans. From the obtained results some structure-activity relationships were outlined.

Microwave-Assisted Synthesis of Novel Pyrazolo[3,4-g][1,8]naphthyridin-5-amine with Potential Antifungal and Antitumor Activity.

The microwave assisted reaction between heterocyclic o-aminonitriles 1 and cyclic ketones 2 catalyzed by zinc chloride led to new series of pyrazolo[3,4-b] [1,8]naphthyridin-5-amines 3 in good yields. This procedure provides several advantages such as being environmentally friendly, high yields, simple work-up procedure, broad scope of applicability and the protocol provides an alternative for the synthesis of pyrazolonaphthyridines. The whole series showed antifungal activities against Candida albicans and Cryptococcus neoformans standardized strains, being compounds with a 4-p-tolyl substituent of the naphthyridin scheleton (3a, 3d and 3g), the most active ones mainly against C. albicans, which appear to be related to their comparative hydrophobicity. Among them, 3d, containing a cyclohexyl fused ring, showed the best activity. The anti-Candida activity was corroborated by testing the three most active compounds against clinical isolates of albicans and non-albicans Candida strains. These compounds were also screened by the US National Cancer Institute (NCI) for their ability to inhibit 60 different human tumor cell lines. Compounds 3a and 3e showed remarkable antitumor activity against cancer cell lines, with the most important GI50 values ranging from 0.62 to 2.18 µM.

Geometric influence on intramolecular photoinduced electron transfer in platinum(II) acetylide-linked donor-acceptor assemblies.

A new donor-acceptor system, in which the electron donor triphenylamine (TPA) and the electron acceptor C60 are bridged through a cis- or trans-platinum(II) acetylide spacer have been prepared. Ground-state studies were conducted using electrochemistry and UV/Vis spectroscopy. Fluorescence studies suggested that charge transfer is the deactivation mechanism for the singlet excited state, and this was verified by transient absorption spectroscopy. Selective photoexcitation of 1 and 2 at 387 nm leads to a fast charge transfer between the TPA and C60, which gives rise to a radical ion-pair state (TPA(·+)-Pt-C60(·-)). Our results suggest that charge transfer is favored for the cis configuration while the presence of the trans configuration in the Pt(II) diacetylide results in a longer-lived charge separated states.