Perylene Diimide-Based Dimeric Electron Acceptors with Molecular Conformations for Perovskite Solar Cells.

This paper reports five novel PDI dimer type electron transport materials (ETMs) employing o-indoloquinoxaline (o-Iq), m-indoloquinoxaline (m-Iq), and cibalackrot (Ci) groups as the core building blocks and presents the twisted structures of PDI dimers coded as PDI-NHR-o-Iq, PDI-o-Iq, PDI-NHR-m-Iq, PDI-m-Iq and PDI-NHR-Ci dyes (see Scheme 1 and 2). We have systematically compared their photophysical, electrochemical, and optoelectronic properties with respect to the reference dye (2PDI-NHR), which is directly connected of two PDI planes. Their calculated HOMO-LUMO energy levels are sufficient for charge transfer to the perovskite material so that structure-photovoltaic performance relationship of synthesized ETM dyes can be evaluated. When the binding position of indoloquinoxaline group between PDI rings are changed from o- to m- positions, most of the photophysical and electrochemical properties of PDI dimer are dramatically changed, finally improving the photovoltaic performances.

Fluorene Based Ferric Complex as Colorimetric and Fluorometric Probe for Highly Selective Detection of CN- and S2- Anions.

A series of new chemosensor molecules bearing benzothiazole-, quinoline- and phthalazine-functionalized fluorene derivatives were synthesized and their complexation behaviors with Fe3+ and Sn2+ ions were investigated. The sensing abilities of their complexes towards both cyanide and sulfide anions were investigated by colorimetric and fluorometric techniques in detail. The sensing mechanism was investigated by Job's and Scatchard plots evaluations, and also absorption/fluorescence titration experiments. Among the studied dye/metal binary systems, F-BT sensor to Fe3+ giving the detection limits of 3.1 µg has also displayed high selectivity and sensitivity towards CN- and S2- anions, lead to a significant color change of the solution observable by the naked eye.

Indigo-Based Acceptor Type Small Molecules: Synthesis, Electrochemical and Optoelectronic Characterizations.

In this paper, we report design and synthesis of novel low bandgap small molecules, indigo-benzimidazole (Tyr-3) and indigo-schiff base (Tyr-4) type acceptors. In these structures, tert-butoxycarbonyl (t-BOC) group has been attached to indigo nitrogen atom in order to increase the solubility. UV-vis absorption spectra of Tyr-3 and Tyr-4 dyes exhibit wide absorption bands ranging from 350 to 600 nm, indicating the relatively low bandgap giving around 2.07 eV for each. Excitation of both Tyr-3 and Tyr-4 dyes at 485 nm displays characteristic emission features of indigo moiety and also intramolecular charge transfer complex (ICT) related with their subunits. Besides increasing fluorescence quantum yields as compared to model compound, biexponential decay times for fluorescence life times were also obtained for Tyr-3 and Tyr-4 dyes. Their appropriate energy levels along with low HOMO levels are desired for light harvesting acceptors for organic solar cells when blended with poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2',1',3'-benzothiadiazole] (PCDTBT) as donor polymer. Photovoltaic behavior of the synthesized dyes were examined in bulk heterojunction concept and achieved photovoltaic conversion efficiencies were discussed.

Synthesis and photophysical characterization of isoindigo building blocks as molecular acceptors for organic photovoltaics.

Five isoindigo-based donor-acceptor-donor (D-A-D) type small molecules have been synthesized in order to investigate their intramolecular charge transfer characteristics. UV-vis absorption of these dyes exhibits a wide absorption band ranging from 300 to 650 nm with two distinct bands, giving the narrow bandgaps between 1.72 and 1.85 eV. Taking into account their HOMO-LUMO energy levels and bandgaps, isoindigo dyes have been used in the active layer of organic solar cell (OSC) devices. When these small molecule semiconductors were used as acceptors with the donor poly(3-hexylthiophene-2,5-diyl (P3HT) polymer in the inverted OSC devices, the highest power conversion efficiency (PCE) was obtained as 0.10% for pyrene-substituted isoindigo derivative.

Optoelectronic performance comparison of new thiophene linked benzimidazole conjugates with diverse substitution patterns.

In an approach to develop efficient organic optoelectronic devices to be used in light-driven systems, a series of three thiophene linked benzimidazole conjugates were synthesized and characterized. The combination of two thiophene rings to a benzimidazole core decorated with different functional groups (such as OCH3, N(CH3)2, CF3) resulted in donor-acceptor type molecular scaffold. The effect of the electronic behavior of the substituents on the optical, electrochemical, morphological and electron/hole transporting properties of the dyes were systematically investigated. DTBI2 dye exhibited distinct absorption properties among the other studied dyes because N,N-dimethylamino group initiated intramolecular charge transfer (ICT) process in the studied solvents. In solid state, the dyes exhibit peaks extending up to 600nm. Depending on the solvent polarities, dyes show significant wavelength changes on their fluorescence emission spectra in the excited states. Morphological parameters of the thin films spin-coated from CHCl3 solution were investigated by using AFM instrument; furthermore photovoltaic responses are reported, even though photovoltaic performances of the fabricated solar cells with different configurations are quite low.

Comparison of the Optoelectronic Performance of Neutral and Cationic Forms of Riboflavin.

The riboflavin dye 2,3,4,5-tetra-O-acetyl-1-[3-(6-bromohexyl)-7,8-dimethyl-2,4-dioxo-3,4-dihydrobenzo[g]pteridin-10(2H)-yl]-1-deoxypentitol and its pyridinium salt were synthesized, and studied by absorption and fluorescence spectroscopy in solutions and on thin film states. The first absorption band of riboflavin-pyridinium salt derivative is red-shifted by 10 nm compared to neutral one on film. Cationic riboflavin derivative shows significant wavelength changes on its fluorescence emission spectrum in the excited state depending on the solvent polarity and the electronic environment. The fluorescence quantum yields of cationic riboflavin gave much higher values as compared to that of its neutral form. The fluorescence lifetimes were found to be in the range of 5.5-6.6 ns with mono - exponential behavior. These dyes possess low-lying HOMO energy levels which are suitable to be able to inject holes to donor polymers so that they can be used as acceptor component in the active layer of bulk heterojunction solar cells (BHJ-SCs). Photovoltaic responses are reported for P3HT:riboflavin active layer wherein the synthesized dyes are used as acceptor component. Also, neutral riboflavin shows greater electron mobility value of 1.3 × 10-3 cm2/V∙s compared to its cationic derivative.

Impact of the different electron-releasing subunits on the dye-sensitized solar cell performance of new triphenylamine-benzimidazole based molecules.

New triphenylamine-benzimidazole type small molecules with different electron-releasing groups were designed and synthesized to investigate their photovoltaic performances in dye sensitized solar cells (DSSCs). Their good visible absorptions covering the 400-535 nm in addition to suitable lowest unoccupied molecular orbital (LUMO) energy levels between -3.03 and -3.11 eV make good candidates them for DSSC devices. Fluorescence quenching studies of the dyes with pristine titania support the good electron injection to conduction band of TiO2. Time resolved measurements of the dyes in solutions indicate the occurence of charge generation during the excited state. One of the used dyes in DSSC devices, TPA5a, carrying a methoxy group in triphenylamine part of the structure, gave much higher power conversion efficiency (PCE) value of 4.31% as compared to the other derivatives. Device fabricated from TPA5a dye gives good external quantum efficiency (EQE) value above 70% at 460 nm. Also, electron impedance spectroscopy (EIS) analysis of the devices gives a good explanation of the understanding of the cell performances.

Targeted singlet oxygen generation using different DNA-interacting perylene diimide type photosensitizers.

Singlet oxygen quantum yields (ΦΔ) of different perylene diimides (PDIs) containing phenyl (PDI-Ph), pyrene (PDI-Pyr), and indole (PDI-In) units in bay positions of the ring were determined using 1,3-diphenylisobenzofuran (DPBF) method in toluene/methanol (99:1) system. Pyrene-substituted PDI were the most efficient singlet oxygen generator among the investigated photosensitizers with a quantum yield of Φ Δ = 0.93 in toluene/methanol. Additionally, their binding affinities to G-quadruplex DNA structure were investigated by steady-state measurements. There were marked red shifts of absorbance bands for PDI-Pyr/DNA strand complexes with respect to the absorption maxima of DNA-free solution of PDI-Pyr in phosphate buffer at pH 6.

Synthesis, characterization and optoelectronic properties of a new perylene diimide-benzimidazole type solar light harvesting dye.

A perylene diimide type small molecule (BI-PDI) has been synthesized through Suzuki coupling reaction between N,N'-bis(2,6-diisopropylphenyl)-1,7-dibromoperylene-3,4,9,10-tetracarboxylic diimide and 2-(2-hydroxyphenyl)-7-phenyl-1H-benzimidazole-4-boronic acid. BI-PDI small molecule has showed an absorption band between 350 and 750 nm on thin films. HOMO and LUMO energy levels of BI-PDI dye have been calculated to be about -5.92 eV and -3.82 eV, respectively. Solution-processed bulk heterojunction (BHJ) solar cells have been constructed using BI-PDI as donor and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) as acceptor or poly(3-hexylthiophene) (P3HT) as donor and BI-PDI as acceptor. The external quantum efficiencies (EQE) of the devices cover the most of the visible region between 400 and 700 nm for both configurations. Photovoltaic performances of BI-PDI-based organic solar cells are limited by the aggregation tendency of PDI structure and poor hole/electron mobilities of the active layer.

Metabolic comparison of radiolabeled aniline- and phenol-phthaleins with (131)I.

The metabolic comparison of aniline- and phenol-phthaleins radiolabeled with (131)I ((131)I-APH and (131)I-PPH, respectively) has been investigated in this study. To compare the metabolic behavior of these phthaleins and their glucuronide conjugates radiolabeled with (131)I, scintigraphic and biodistributional techniques were applied using male Albino rabbits. The results obtained have shown that these compounds were successfully radioiodinated with a radioiodination yield of about 100%. Maximum uptakes of (131)I-APH and (131)I-PPH, which were metabolized as N- and O-glucuronides, were observed within 2 h in the bladder and in the small intestine, respectively. In the case of verification of considerably up taking of these compounds also by tumors developed in the small intestine and in the bladder tissues, these results can be expected to be encouraging to test these compounds, which will be radiolabeled with other radioiodines such as (125)I, (123)I and (124)I as imaging and therapeutic agents in nuclear medical applications.

Photophysical study of photoinduced electron transfer in a bis-thiophene substituted peryleneimide.

Based on femtosecond time-resolved spectroscopy and single photon timing experiments, intramolecular photoinduced charge transfer has been investigated in two systems containing a peryleneimide chromophore (P) and thiophene (T) groups. The first compound bearing a single thiophene ring (PT1) is used as model and shows a behavior similar to P, studied previously, while in the compound with two thiophene rings attached (PT2) electron transfer from the thiophene donor to the peryleneimide acceptor is observed in benzonitrile. Femtosecond fluorescence upconversion and femtosecond transient absorption experiments in benzonitrile indicate that this ion-pair state formation occurs in 19 ps. This ion-pair state then decays with two time constants of 1400 and 820 ps, probably corresponding to different conformations of the thiophene rings.