Ullazine Donor–π bridge‐Acceptor Organic Dyes for Dye‐Sensitized Solar Cells

Divergent Synthesis of 5,7-Diazaullazines Derivatives through a Combination of Cycloisomerization with Povarov or Alkyne-Carbonyl Metathesis

Ullazines and their π-expanded derivatives have gained much attention as active components in various applications, such as in organic photovoltaic cells or as photosensitizers for CO2 photoreduction. Here, we report the divergent synthesis of functionalized diazaullazines by means of two different domino-reactions consisting of either a Povarov/cycloisomerization or alkyne-carbonyl metathesis/cycloisomerization protocol. The corresponding quinolino-diazaullazine and benzoyl-diazaullazine derivatives were obtained in moderate to good yields. Their optical and electronic properties were studied and compared to related, literature-known compounds to obtain insights into the impact of nitrogen doping and π-expansion.

Synthesis and Properties of 5-Azaullazines

5-Azaullazines, indolizino[6,5,4,3-ija][1,5]naphthyridines, and their benzo-fused analogues were prepared in three steps by combination of Pd catalyzed cross-coupling reactions with Brønsted acid mediated cycloisomerisations. The reaction tolerates various substitution patterns and functional groups and proceeds in high yields. Optical and electrochemical properties of selected products were studied experimentally and by DFT calculations.

Rhodium(III)-Catalyzed Intramolecular Annulation and Aromatization for the Synthesis of Pyrrolo[1,2-a]quinolines

A rhodium(III)-catalyzed protocol for the synthesis of pyrrolo[1,2-a]quinolines through intramolecular annulation of o-alkynyl amino aromatic ketones and subsequent aromatization is reported. This transformation builds the pyrrole and quinoline moieties of the pyrrolo[1,2-a]quinoline in one pot and achieves a flexible introduction of different substituent groups at 4- and 5-positions on products that were difficult to prepare by other means. The reaction proceeds smoothly on a gram scale, and the products are amenable to downstream synthetic manipulations.

Design and DFT study of nitrogen-rich donor systems for improved photovoltaic performance in dye-sensitized solar cells

Donor modifications, especially through N-annulation, for enhancing the structure–performance relationship of D–π–A systems for DSSC applications.

Robust, Scalable Synthesis of the Bulky Hagfeldt Donor for Dye-Sensitized Solar Cells

The bulky triarylamine group commonly referred to as the "Hagfeldt donor" is a key building block found in many of the organic dyes used in dye-sensitized applications such as dye-sensitized solar cells (DSCs). This building block has gained popularity owing to its presence in many of the best-performing DSC devices reported to date, which use dyes containing this donor group. The Hagfeldt donor provides a desirable 3-dimensional structure that aids in surface protection of electrons injected into the semiconductor from oxidants in the electrolyte, allowing for record-setting cobalt- and copper-based redox shuttles to be utilized more frequently. However, the synthesis of this molecule has proven unreliable for many routes. This study concerns a novel, reliable and scalable five-step synthesis of the Hagfeldt donor.

Density functional theory study on the donating strength of donor systems in dye-sensitized solar cells

Donating strength of typically used donors in dye-sensitized solar cells.

Molecular engineering of the alkyl chain in planar carbazole dyes toward efficient interfacial charge transfer processes

With the extension of the alkyl chain, the interfacial charge transfer processes are effectively improved.

Symmetrical and unsymmetrical fluorine-rich ullazines via controlled cycloaromatizations

The synthesis of a series of electron-deficient pentafluorosulfanylated ullazines (U1–U10) by sequential electrophilic cycloaromatizations has been achieved.

Near-Infrared-Absorbing Indolizine-Porphyrin Push-Pull Dye for Dye-Sensitized Solar Cells

Porphyrins are attractive chromophores for application in dye-sensitized solar cells (DSCs), as judicious tuning of donor-acceptor properties can enable excellent near-infrared (NIR) absorption and exceptional device performance. Here, we report a porphyrin-based dye (SM85) conjugated to the planar strong electron donor, indolizine, designed to extend absorption further into the NIR region by inducing π-π interactions such as head-to-tail dye aggregation. The optoelectronic consequences of indolizine incorporation in SM85 include raising the ground-state oxidation potential and broadening and red-shifting ultraviolet-visible-NIR absorptions, along with increased molar absorptivity when compared to the dye SM315. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations confirm the push-pull character of SM85, which features an overlap of frontier occupied and unoccupied orbitals. Steady-state spectrophotometric analyses reveal the presence of solution aggregates via absorption and emission spectroscopies. Aggregate modes were probed by DFT and TD-DFT analyses, and plausible models are presented. SM85-based DSC devices demonstrate a 5.7% power conversion efficiency (PCE) at full sun (7.4% PCE at 10% sun) with an exceptional improvement to the incident photon-to-current conversion onset at ∼850 nm. Current dynamics measurements, time-correlated single photon counting, and computational analyses are used to better understand device performances. This study puts forward a novel intramolecular charge-transfer porphyrin system with a dramatic shift into the NIR region, as is needed for nonprecious metal-based sensitizers, and provides an example of controlled, donor-acceptor-mediated aggregation as a complementary strategy to traditional donor-acceptor modifications to single-molecule π-systems in accessing enhancements in long wavelength light harvesting in molecular-based optoelectronic devices.

Synthesis of near-infrared absorbing and fluorescing thiophene-fused BODIPY dyes with strong electron-donating groups and their application in dye-sensitised solar cells

Thiophene-fused BODIPY dyes with two diethylaminophenyl groups as strong donors demonstrated near-infrared (NIR) absorption (λ_max: 783–812 nm, ε: 119 500–145 900) and fluorescence (F_max: 862–916 nm, Φ_f: 0.02–0.12) in dichloromethane.

Origin of Panchromaticity in Multichromophore-Tetrapyrrole Arrays

Panchromatic absorbers that have robust photophysical properties enable new designs for molecular-based light-harvesting systems. Herein, we report experimental and theoretical studies of the spectral, redox, and excited-state properties of a series of perylene-monoimide-ethyne-porphyrin arrays wherein the number of perylene-monoimide units is stepped from one to four. In the arrays, a profound shift of absorption intensity from the strong violet-blue (B _y and B _x) bands of typical porphyrins into the green, red, and near-infrared (Q _x and Q _y) regions stems from mixing of chromophore and tetrapyrrole molecular orbitals (MOs), which gives multiplets of MOs having electron density spread over the entire array. This reduces the extensive mixing between porphyrin excited-state configurations and the transition-dipole addition and subtraction that normally leads to intense B and weak Q bands. Reduced configurational mixing derives from moderate effects of the ethyne and perylene on the MO energies and a more substantial effect of electron-density delocalization to reduce the configuration-interaction energy. Quantitative oscillator-strength analysis shows that porphyrin intensity is also shifted into the perylene-like green-region absorption and that the ethyne linkers lend absorption intensity. The reduced porphyrin configurational mixing also endows the S₁ state with bacteriochlorin-like properties, including a 1-5 ns lifetime.

Quinoxaline-Based Dual Donor, Dual Acceptor Organic Dyes for Dye-Sensitized Solar Cells

A novel metal-free quinoxaline-based molecular framework with a dual donor and dual acceptor (DD-π-AA) motif has been introduced. Four sensitizers (AP6, AP8, AP9, and AP12) have been synthesized and fully characterized via UV–Vis absorption, cyclic voltammetry, density functional theory (DFT) calculations, time-correlated single photon counting (TCSPC), and in dye-sensitized solar cell (DSC) devices. Structural modifications to both the donor and acceptor/anchor regions were evaluated via structure–property relationships without altering the quinoxaline π-bridge. Through careful dye design, a broadly absorbing near-infrared (NIR) sensitizer extending electricity production to 800 nm is realized in DSC devices. Ground- and excited-state oxidation potentials were measured to show energetically favorable charge transfer events. Importantly, the dye structure was found to have a strong influence on dye energetics in different environments with structural elements allowing for either similar or dramatically different solution versus film measurements. The DSC device electrolyte was also found to have a significant influence on dye energetics as well. Electron transfer events were probed for each dye with DSC device measurements and with TCSPC studies. The results are correlated to the dye structures.