We report a nontraditional synthesis of cyclopentafused-polycyclic aromatic hydrocarbon embedded ladder polymers using a palladium catalyzed cyclopentannulation polymerization followed by a cyclodehydrogenation reaction. Donor–acceptor type polymers containing a cyclopenta[hi]aceanthrylene acceptor groups can be synthesized by a palladium catalyzed copolymerization between 9,10-dibromoanthracene and a variety of bis(arylethynyl)arenes to give polymers with molecular weights (Mn) of 9–22 kDa. The bis(arylethynyl)arenes were composed of benzene, thiophene, or thieno[3,2-b]thiophene moieties, which provided access to a series of four donor–acceptor copolymers. The polymers were subjected to cyclodehydrogenation with FeCl3 to access rigid ladder type polymers with the conversion investigated by 13C NMR of isotopically labeled polymers. The ladder polymers possess broad UV–Vis absorptions and narrow optical band gaps of 1.17–1.29 eV and are p-type semiconductors in organic field effect transistors.

In this manuscript, we report a design strategy to control polychromophore polymer folding at the single molecule level through hydrogen-bonding (H-bonding) interactions. Polymers composed of bis(2-ethylhexyl)-p-phenylene vinylene (BEH-PPV) oligomers (trimers) containing H-bonding capable side-chains (e.g., carboxylic acid or urea units) were prepared by copolymerization with flexible linkers. Control polymers with masked H-bonding side-chains (e.g., t-butyl ester) were also prepared. Different polymer folding schemes are proposed including random or non-folding for the control polymers, and side-on and face-on geometries for the carboxylic acid and urea motifs, respectively. Single molecule excitation polarization spectroscopy demonstrates that the highest folding order is achieved with the urea containing side-chains and isotropic folding is found in polymers that do not contain H-bonding units. We propose that the effects of the chromophore conformational geometries and the type of H-bonding are additive and lead to highly aligned urea-containing polymers. In addition, an examination of the individual polymers’ spectral signatures via single molecule spectroscopy showed an overall red-shift of ∼0.06 eV in the 0–0 origin peak for the urea-containing polymer compared to the other two polymer systems. This spectral shift is attributed to planarization of the backbone and further supports the presence of a highly ordered urea-containing polymer structure. Utilization of this H-bonding inclusion synthetic strategy to control polymer secondary structure could provide important design elements for future functional material design.

We show that a new class of contorted polycyclic aromatic hydrocarbons (PAHs) containing five-membered rings can be prepared via a palladium-catalyzed cyclopentannulation followed by Scholl cyclodehydrogenation. The annulation chemistry can be accomplished between a di-arylethynylene and an appropriate aryl-dibromide to form 1,2,6,7-tetraarylcyclopenta[hi]aceanthrylenes and 1,2,6,7-tetraaryldicyclopenta[cd,jk]pyrenes. Scholl cyclodehydrogenation to close the externally fused aryl groups was accomplished only with properly arranged alkoxy substitutions and provides access to the pi-extended 2,7,13,18-tetraalkoxytetrabenzo[f,h,r,t]rubicenes and 2,7,13,18-tetraalkoxydibenzo[4,5:6,7]indeno[1,2,3-cd]dibenzo[4,5:6,7]indeno[1,2,3-jk]pyrenes. The final compounds each possess apparent [4]helicene-like arrangements with fused five-membered rings; however, only the 2,7,13,18-tetraalkoxytetrabenzo[f,h,r,t]rubicenes contort out of planarity owing to an additional [5]helicene like arrangement. Single crystal analysis of the contorted aromatic shows the PAHs stack in a lock-and-key like arrangement and pi-stack in a columnar arrangement. Solution-phase aggregation, as well as liquid crystalline mesophases, were found for derivatives with suitably attached solubilizing chains.

A series of reduced band gap donor–acceptor copolymers that contain electron accepting 1,2,6,7-tetra(4-dodecylphenyl)dicyclopenta[cd,jk]pyrene were prepared. The hydrocarbon acceptor relies on its cyclopenta-fused polycyclic aromatic hydrocarbon (CP-PAH) character to access a relatively reduced lowest unoccupied molecular orbital. The donor unit was varied between thiophene, bithiophene, and 1,4-diethynyl-2,5-bis(octyloxy)-benzene producing polymers with band gaps between 1.69–1.74 eV. The synthetic methodology as well as the optoelectronic properties of the donor–acceptor copolymers, including thin-film absorption and cyclic voltammetry, are presented.

A one-step postpolymerization modification that converts three high bandgap poly(arylene ethynylene)s into low bandgap donor–acceptor copolymers is described. The strategy relies on a palladium-catalyzed cyclopentannulation reaction between the main-chain ethynylene functionality and a small molecule aryl bromide (6-bromo-1,2-dimethylaceanthrylene). The reaction installs new cyclopenta[hi]aceanthrylene electron-accepting groups between the electron rich arylenes along the polymer backbone. The modified polymers include poly(9,9-didodecyl-fluorene-2,7-ethynylene), poly(9-dodecyl-carbazole-2,7-ethynylene), and poly(2,5-dioctyloxyphenylene-1,4-ethynylene). The functionalization efficiency was evaluated via isotopic 13C labeling of the polymeric ethynylene carbons and then monitoring the chemical environment of those carbons via NMR spectroscopy. Near complete conversion of the sp carbon species to sp2 carbon species was observed, which demonstrates the high efficiency of the modification strategy. Gel permeation chromatography shows that the hydrodynamic radius of the polymers is reduced considerably going from linear to kinked polymer morphology upon functionalization, and molecular dynamics simulations illustrate the underlying morphological change. The newly formed donor–acceptor polymers showed dramatically different optical and electrochemical properties from the precursor poly(arylene ethynylene) polymers. A new absorption band centered at ∼650 nm represents a red-shift of >300 nm for the onset of absorption compared with that of precursor polymers and cyclic voltammetry shows two new low-lying reduction peaks that coincide with the cyclopenta[hi]aceanthrylene moiety.

The synthesis and morphological investigation of a series of polychromophore polymers composed of oligomeric bis(2-ethylhexyl)-p-phenylenevinylene (BEH-PPV) (trimer, pentamer, and heptamer) monomers copolymerized with rigid morphological directing groups (morphons) are described. The polymerization was carried out using a Sonogashira cross-coupling polymerization between monomers composed of an iodo-terminated BEH-PPV oligomer and a bis(phenylacetylene)-containing morphon. The rigid morphons are prepared from adamantane and diamantane frameworks that are composed solely of sp3 carbons, inhibit conjugation between BEH-PPV oligomers, and direct the local polymer morphology in either a bent or linear vector, respectively. The morphological properties of the polychromophore polymers were interrogated via single molecule fluorescence spectroscopy, thin-film absorption and fluorescence spectroscopy, and atomic force microscopy. Significant morphological variation was found upon substituting the morphon, as well as the chromophore size, with the most ordered structures being accessed with diamantane morphons.

We demonstrate the preparation of diacenaphthopentalene derivatives via a palladium-catalyzed dimerization of 1-iodo-2-arylethynyl-acenaphthylenes. The resulting 7,14-diarylpentaleno[1,2-a:4,5a′]diacenaphthylenes, which contain four linearly fused five-membered rings, are benchtop stable and behave as hole-transporting or ambipolar semiconductors in organic field effect transistors. The X-ray crystal structure shows the important role of the fused naphthalene unit that enforces a formal pentalene subunit at the central five-membered rings and [5]-radialene-like structures at the proximal five-membered rings. Nucleus-independent chemical shift (NICS) calculations show the internal pentalene rings are intermediate in antiaromaticity character between known pentalene and dibenzopentalenes derivatives. The diacenaphthopentalene derivatives give high optical gap materials owing to a forbidden HOMO to LUMO transition, yet have narrow electrochemical gaps and are reduced at small negative potentials giving LUMO energy levels of −3.57 to −3.74 eV.

A series of substituted cyclopenta[hi]aceanthrylene derivatives with electron donating (NH2, OCH3), neutral (H), and electron withdrawing (COOH, CF3, CN, NO2) substituents were prepared. A room-temperature Sonogashira cross-coupling reaction between 2,7-dibromocyclopenta[hi]aceanthrylene and an appropriately functionalized phenylene ethynylene precursor was utilized to access the materials that were characterized by Nuclear Magnetic Resonance Spectroscopy (NMR), cyclic voltammetry (CV), and UV–Vis spectroscopy. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were systematically varied when proceeding from electron donating to electron withdrawing substituents. The optical band gap was significantly altered for the most electron donating species, while little change was observed between different electron withdrawing substituents. This study demonstrates the ability to control the frontier orbital energies of this class of cyclopenta-fused polycyclic aromatic hydrocarbon materials through selective substitution.

A series of three pentameric derivatives of 2-methoxy-5-(2′-ethylhexyloxy)-p-phenylenevinylenes (2–4), with varying degrees of side chain regioregularity, was prepared. The oligomerization chemistry was carried out using repetitive Horner–Wadsworth–Emmons (HWE) reactions of precisely substituted aryl rings with four different substituents. The resulting oligomers were characterized by nuclear magnetic resonance spectroscopy (NMR), cyclic voltammetry (CV) and absorption spectroscopy in solution and in thin films. Each of the oligomers gave discrete 1H and 13C NMR spectra. The regioregular pentamer (2) displayed the most resolution between signals and suggests those nuclei reside in more unique chemical environments than the regiorandom pentamers (3 and 4). The solution phase electronic (CV) and absorption properties of each of the new oligomers were found to be essentially identical. In contrast, the thin film absorption spectra were not equivalent. The more regioregular pentamers (2 and 3) possessed a new, red-shifted shoulder structure that suggests the packing order is heavily influenced by side chain regioregularity even at the pentamer level.

A synthetic strategy to prepare 2,7- or 4,9-functionalized cyclopenta[hi]aceanthrylenes that are capable of Suzuki cross-coupling reactions is demonstrated. This method has been utilized to create a series of thiophene derivatized compounds that were subsequently used to investigate the role of substitution pattern on the photophysical and electronic properties of cyclopenta[hi]aceanthrylenes. The orthogonal functionalization provides access to unique substitution patterns (e.g., cruciform-like architectures) and materials with small optical band gaps (1.22–1.97 eV).

We report the synthesis and selective functionalization of two externally fused cyclopenta-fused polycyclic aromatic hydrocarbons (CP-PAHs) and demonstrate their electron accepting behavior. 2,7-Bis(trimethylsilyl)cyclopenta[hi]aceanthrylene (1) and 2,8-bis(trimethylsilyl)dicyclopenta[de,mn]tetracene (4) were prepared in a one-pot, palladium-catalyzed cross-coupling of (trimethylsilyl)acetylene and either 9,10-dibromoanthracene or 5,11-dibromotetracene, respectively. The trimethylsilyl groups were selectively converted into bromides via substitution with N-bromosuccinimide to create universal partners (2 and 6) for metal-catalyzed cross-coupling reactions. To demonstrate the utility of the halogenated CP-PAHs, we successfully employed a Sonogashira cross-coupling between the CP-PAHs and a phenylacetylene derivative. The resulting compounds (3 and 7) were found to be highly conjugated between the CP-PAH core and the substituents, as demonstrated by large bathochromic shifts in the absorption spectra as well as density functional theory calculations. Ethynylated CP-PAHs 3 and 7 were found to possess low optical bandgaps (1.52 and 1.51 eV, respectively) and displayed two reversible reductions. We further demonstrated the fullerene-like electron-accepting behavior of 3 through solution-phase fluorescence quenching of the prototypical electron donor, poly(3-hexylthiophene).

A series of alternating copolymers containing oligomeric bis(2-ethylhexyl)-p-phenylenevinylene (BEH-PPV) chromophores and conformational-flexible n-decyl or tetraethylene glycol chains were prepared. The polymerization was carried out using Sonogashira coupling conditions between monomers composed of an iodo-terminated PPV oligomer (trimer, pentamer, or septamer) and a bis(phenylacetylene)-containing flexible chain. Polymers containing the n-decyl chain attained higher molecular weights compared to the tetraethylene glycol-containing polymers. 4-Ethynylanisole-capped oligomers (trimer, pentamer, or septamer) were prepared, and their solution photophysical properties were compared to the analogous polymeric materials. The solution optical properties of the polymers were primarily determined by chromophore length of the constituent oligomers. In contrast, the thin film fluorescence spectra of the polymers showed substantial differences between n-decyl and tetraethylene glycol containing materials, suggesting significant changes in the degree of interchain coupling in the solid state. The control of effective conjugation length afforded by these materials makes them a promising system for understanding electronic trap states in conjugated polymers.

We show that a new class of contorted polycyclic aromatic hydrocarbons (PAHs) containing five-membered rings can be prepared via a palladium-catalyzed cyclopentannulation followed by Scholl cyclodehydrogenation. The annulation chemistry can be accomplished between a di-arylethynylene and an appropriate aryl-dibromide to form 1,2,6,7-tetraarylcyclopenta[hi]aceanthrylenes and 1,2,6,7-tetraaryldicyclopenta[cd,jk]pyrenes. Scholl cyclodehydrogenation to close the externally fused aryl groups was accomplished only with properly arranged alkoxy substitutions and provides access to the pi-extended 2,7,13,18-tetraalkoxytetrabenzo[f,h,r,t]rubicenes and 2,7,13,18-tetraalkoxydibenzo[4,5:6,7]indeno[1,2,3-cd]dibenzo[4,5:6,7]indeno[1,2,3-jk]pyrenes. The final compounds each possess apparent [4]helicene-like arrangements with fused five-membered rings; however, only the 2,7,13,18-tetraalkoxytetrabenzo[f,h,r,t]rubicenes contort out of planarity owing to an additional [5]helicene like arrangement. Single crystal analysis of the contorted aromatic shows the PAHs stack in a lock-and-key like arrangement and pi-stack in a columnar arrangement. Solution-phase aggregation, as well as liquid crystalline mesophases, were found for derivatives with suitably attached solubilizing chains.