Graham E. Morse

Boron Subphthalocyanines as Organic Electronic Materials

Boron subphthalocyanines (BsubPcs) are an emerging class of high performing materials in organic electronics. Since the first use of chloroboron subphthalocyanine in an organic electronic device 6 years ago subphthalocyanines have shown potential as functional materials in organic light emitting diodes (OLEDs) and organic photovoltaics (OPVs). Here we review the material properties of chloroboron subphthalocyanine (Cl-BsubPc) and its use as an organic semiconductor. We then highlight our efforts toward derivatives of boron subpthalocyanine beyond Cl-BsubPc and discuss the impact of molecular design on the material properties and the performance of the BsubPc. Finally, we comment on the status of BsubPcs in the field of organic electronics and discuss how we believe future progress can be made.

Pentafluorophenoxy Boron Subphthalocyanine As a Fluorescent Dopant Emitter in Organic Light Emitting Diodes

A fluorinated phenoxy boron subphthalocyanine (BsubPc) is shown to function as a fluorescent dopant emitter in small molecule organic light emitting diodes (OLEDs). Narrow electroluminescence (EL) emission with a full width at half-maximum of ∼30 nm was observed regardless of the host used, indicating that this narrow EL is intrinsic to the BsubPc molecule. A bathochromic shift and the growth of a new EL peak at higher wavelengths with increasing doping concentration were found to be a result of molecular aggregation. Excitation of BsubPc by direct charge trapping as well as Förster resonant energy transfer were shown using different host molecules. A maximum efficiency of 1.5 cd/A was achieved for a 4,4-N,N-dicarbazole-biphenyl (CBP) host.

Phthalimido-boronsubphthalocyanines: new derivatives of boronsubphthalocyanine with bipolar electrochemistry and functionality in OLEDs.

Phthalimides have been found to react with Cl-BsubPc to produce a new class of BsubPc derivatives, phthalimido-boronsubphthalocyanines (Phth-BsubPcs). They exhibit a high quantum yield for photoluminescence (Φ), maintain a high molar extinction coefficient (ε) and have bipolar electrochemical stability previously unseen in simple BsubPc derivatives. Their bipolar electrochemical characteristics have been extended into simple organic electronic devices: in OLEDs as charge transporters and emitters.

Pentafluorophenoxy boron subphthalocyanine (F5BsubPc) as a multifunctional material for organic photovoltaics.

We have demonstrated that pentafluoro phenoxy boron subphthalocyanine (F5BsubPc) can function as either an electron donor or an electron acceptor layer in a planar heterojunction organic photovolatic (PHJ OPV) cell. F5BsubPc was incorporated into devices with the configurations ITO/MoO3/F5BsubPc/C60/BCP/Al (F5BsubPc used as an electron-donor/hole-transport layer) and ITO/MoO3/Cl-BsubPc/F5BsubPc/BCP/Al (F5BsubPc used as an electron-acceptor/electron-transport layer). Each unoptimized device displayed open-circuit photopotentials (Voc) close to or in excess of 1 V and respectrable power conversion efficiencies. Ultraviolet photoelectron spectroscopy (UPS) was used to characterize the band-edge offset energies at the donor/acceptor junctions. HOMO and LUMO energy level offsets for the F5BsubPc/C60 heterojunction were determined to be ca. 0.6 eV and ca. 0.7 eV, respectively. Such offsets are clearly large enough to produce rectifying J/V responses, efficient exciton dissociation, and photocurrent production at the interface. For the Cl-BsubPc/F5BsubPc heterojunction, the estimated offset energies were found to be ca. 0.1 eV. However, reasonable photovoltaic activity was observed, with photocurrent production coming from both BsubPc species layers. Incident and absorbed photon power conversion efficiencies (IPCE and APCE) showed that photocurrent production qualitatively tracked the absorbance spectra of the donor/acceptor heterojunctions, with some additional photocurrent activity on the low energy side of the absorbance band. We suggest that photocurrent production at higher wavelengths may be a result of charge-transfer species at the donor/acceptor interface. Cascade photovoltaics were also fabricated to expand on the understanding of the role of F5BsubPc in such device architectures.

Pseudohalides of boron subphthalocyanine.

The synthesis and study of a series of pseudohalides of boron subphthalocyanine (BsubPc) are reported. Each pseudohalide has been compared to the more common chloride and bromide of BsubPc, and we have found that most react slower under standard phenoxylation and hydrolysis conditions. Three pseudohalides (TsO-BsubPc, MsO-BsubPc, and BsO-BsubPc) do not hydrolyze at all even after prolonged periods of time in the presence of water. Single crystals of TsO-, MsO-, and ClsO-BsubPc were obtained, and their structures were unambiguously determined.

Aluminum chloride activation of chloro-boronsubphthalocyanine: a rapid and flexible method for axial functionalization with an expanded set of nucleophiles.

We have developed a process whereby chloro-boronsubphthalocyanine (Cl-BsubPc) and other BsubPcs are activated to reaction with oxygen, sulfur, and nitrogen based nucleophiles by treatment with aluminum chloride under mild conditions. This allows for the scope of atoms chemically bound to the boron atom to be expanded beyond those derived from the traditional oxygen and carbon based nucleophiles. The successful formation of thiophenoxy and phenylamino derivatives of BsubPc was confirmed spectroscopically and by X-ray crystallography of single crystals. We have proposed a detailed mechanism for this process based on experimental observation and NMR spectroscopy ((1)H, (11)B, and (27)Al) which involves formation of a complex between a halo-BsubPc and AlCl(3) (which we denote BsubPc(Cl)·Al(Cl)(3)). Our observations indicate that the action of phenol on BsubPc(Cl)·Al(Cl)(3) does not involve direct reaction at the boron atom; rather phenol first reacts at the aluminum atom along the way to the formation of a new intermediate complex BsubPc(OPh)·Al(OPh)(3). The consequence is that the rate of this process is independent of the nature of the starting BsubPc. Cl-BsubPc and Br-BsubPc as well as BsubPcs with peripheral substitutents all react to form their respective phenoxy derivatives at the same rate. Quenching of BsubPc(OPh)·Al(OPh)(3) with a Lewis base ultimately produces a new bond between the phenol nucleophile and the boron atom of the BsubPc.

(Dodecafluorosubphthalocyaninato)(4-methylphenolato)boron(III).

In the title compound, C31H7BF12N6O, molecules are arranged into one-dimensional columns with an intermolecular B⋯B distance of 5.3176u2005(8)u2005Å. Bowl-shaped molecules are arranged within the columns in a concave bowl-to-ligand arrangement separated by a ring centroid distance of 3.532u2005(2)u2005Å between the benzene ring of the 4-methylphenoxy ligand and one of the three five-membered rings of a symmetry-related molecule.