Use of Piers-Rubinsztajn Chemistry to Access Unique and Challenging Silicon Phthalocyanines.

Axial functionalization is one mode that enables the solubility of silicon phthalocyanines (SiPcs). Our group observed that the use of typical axial functionalization methodologies on reaction of Cl2SiPc with the chlorotriphenyl silane reagent unexpectedly resulted in the equal formation of triphenyl silyloxy silicon tetrabenzotriazacorrole ((3PS)-SiTbc) and the desired bis(tri-phenyl siloxy)-silicon phthalocyanine ((3PS)2-SiPc). The formation of a (3PS)-SiTbc was unexpected, and the separation of (3PS)-SiTbc and (3PS)2-SiPc was difficult. Therefore, in this study, we investigated the use of Piers-Rubinsztajn (PR) chemistry as an alternative method to functionalize the axial position of a SiPc to avoid the generation of a Tbc derivative. PR chemistry is a novel method to form a Si-O bond starting with a Si-H-based reactant and a -OH-based nucleophile enabled by tris(pentafluorophenyl)borane as a catalyst. The PR chemistry was screened on several fronts on how it can be applied to SiPcs. It was found that the process needs to be run in nitrobenzene at a molar ratio and at a particular temperature. To this end, the triphenylsiloxy derivative (3PS)2-SiPc was produced and fully characterized, without the production of a Tbc derivative. In addition, we explored and outlined that the PR chemistry method can enable the formation of other SiPc derivatives that are inaccessible utilizing other established axial substitution chemistry methods such as (TM3)2-SiPc and (MDM)2-SiPc. These additional materials were also physically characterized. The main conclusion is that the PR chemistry method can be applied to SiPcs and yield several alternative derivatives and has the potential to apply to additional macrocyclic compounds for unique derivative formation.

Initial Engineering and Outdoor Stability Assessment of "Gray/Black" Fullerene-Free Organic Photovoltaics Based on Only Two Complementary Absorbing Materials: A Tetrabenzotriazacorrole and a Subphthalocyanine.

Broad absorption is a desired characteristic of materials employed in the photoactive layers of organic photovoltaic (OPV) devices. Here, we have identified tetrabenzotriazacorroles (Tbcs) as complementary absorbing chromophores and electron donors to the promising nonfullerene acceptors boron subphthalocyanines (BsubPcs). These two materials, which can be utilized as donor-acceptor pairs within fullerene-free OPVs, yield spectral coverage over the entire visible range of 300-750 nm. Oxy phosphorus Tbc derivative (POTbc) was employed as an electron donor and paired initially with multiple BsubPc derivatives having a distribution of highest occupied molecular orbital/lowest unoccupied molecular orbital energy levels in planar heterojunction OPVs. These devices were "gray/black" due to the broad absorption across the visible spectrum. Upon screening, the partially halogenated chloro hexachloro BsubPc (Cl-Cl6BsubPc) showed the greatest promise for coupling with POTbc. The thickness ratio and total thickness of the active layer were then probed in order to identify the optical and electrical limitations on the POTbc/Cl-Cl6BsubPc-based OPV device. A maximum power conversion efficiency (PCE) of 2.13% was achieved at 60 nm total thickness of the active layer and 1 to 3 (POTbc to Cl-Cl6BsubPc) thickness ratio. Outdoor stability of the champion device was evaluated using protocols established by International Summits on OPV Stability and was found to be on par with an α-sexithiophene/Cl-Cl6BsubPc baseline OPV.

Straightforward and Relatively Safe Process for the Fluoride Exchange of Trivalent and Tetravalent Group 13 and 14 Phthalocyanines.

To avoid the use of hydrofluoric acid, a series of fluorinated trivalent and tetravalent metal-containing phthalocyanines (MPcs) were synthesized using a straightforward one-step halide substitution process using cesium fluoride (CsF) as the fluoride source and by reflux in N,N-dimethylformamide for less than an hour. The resulting fluoro MPcs were characterized and compared to the parent chloro MPcs. In some cases, very little change in properties was observed between the fluoro MPcs and the chloro MPcs. In other cases, such as fluoro aluminum phthalocyanine, a blue shift in the absorbance characteristics and an increase in oxidation and reduction potential of as much as 0.22 V was observed compared to the chloro derivative. Thermo gravimetric analysis was performed on all halo-MPcs, indicating that the choice of halo substitution on the axial position can have an effect on the decomposition or sublimation temperature of the final compound. After initial establishment and characterization of the fluoro MPcs, the halide substitution reaction of difluoro silicon phthalocyanine (F2-SiPc) was further explored by scaling the reaction up to a gram scale as well as considering tetrabutylammonium fluoride (TBAF) as an additional safe fluoride source. The scaled-up reactions producing F2-SiPc using CsF and TBAF as fluoride exchange sources were successfully reproducible, resulting in reaction yields of 100 and 73%, respectively. Both processes led to pure final products but results indicate that CsF, as the fluoride exchange reagent, appears to be the superior reaction process as it has a much higher yield.

A Comprehensive Scope of Peripheral and Axial Substituent Effect on the Spectroelectrochemistry of Boron Subphthalocyanines.

An extensive study of the electrochemical and spectroelectrochemical properties of 14 boron subphthalocyanine (BsubPc) derivatives with various axial and peripheral substituents was performed in 1,2-dichloromethane (CH2Cl2) containing 0.1 M tetra- n-butyl-ammonium perchlorate (TBAP) as the supporting electrolyte. From the cyclic voltammetry results, all compounds exhibit one oxidation and at least two reduction processes within the solvent potential window of +1.6 to -1.8 V vs SCE. It was found that the reversibility of the redox reactions depends on the axial and peripheral substituents and the dipole moment of the boron-to-axial substituent. In general, UV-vis absorption spectra of the singly reduced BsubPc derivatives exhibit three equal intensity peaks in the 450 to 650 nm region that are derived from the maximum BsubPc absorbance peak upon reduction. Axial substituents affect the intensity of the three peaks upon reduction, while peripheral substituents shift the position of the peaks to higher wavelengths. Upon oxidation, the UV-vis absorption profile flattens considerably with only a single broad (∼300 nm) band apparent. Understanding the effect of substituents on the stability of the redox processes of BsubPcs will aid in further development of these materials for applications in organic electronic devices.

Versatile Synthesis of Siloxy Silicon Tetrabenzotriazacorroles and Insight into the Mode of Macrocycle Formation.

Tetrabenzotriazacorroles (Tbcs) are a family of molecules related to phthalocyanines but have the unique ability to intensely absorb both blue and red light. Here, we report the synthesis of four novel silicon tetrabenzotriazacorrole derivatives (SiTbcs) with varying sized axial ligands. SiTbcs are formed starting from bis(hydroxy) silicon phthalocyanine ((OH)2-SiPc) via a simple in situ axial functionalization and reductive chemical process using magnesium metal and the respective chlorosilane in pyridine. Systematic probing of the reaction conditions revealed that the reaction is acid-promoted and that the formation of the Tbc macrocycle occurs at temperatures as low as 40 °C. Results imply this chemistry can be extended to SiTbcs with any axial ligands using pyridine hydrochloride as an acid source. Single crystals of all compounds were grown and showed significant π-π interactions between the macrocycles in the solid state. Optical, electrochemical, and thermal characterization of these materials is also described. The SiTbcs exhibit interesting highly oxidative electrochemistry as well as high thermal stability and tunable phase transition behavior.