Timothy P. Bender

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.

Phthalocyanine-Based Organic Thin-Film Transistors: A Review of Recent Advances.

Metal phthalocyanines (MPcs) are versatile conjugated macrocycles that have attracted a great deal of interest as active components in modern organic electronic devices. In particular, the charge transport properties of MPcs, their chemical stability, and their synthetic versatility make them ideal candidate materials for use in organic thin-film transistors (OTFTs). This article reviews recent progress in both the material design and device engineering of MPc-based OTFTs, including the introduction of solubilizing groups on the MPcs and the surface modification of substrates to induce favorable MPc self-assembly. Finally, a discussion on emerging niche applications based on MPc OTFTs will be explored, in addition to a perspective and outlook on these promising materials in OTFTs. The scope of this review is focused primarily on the advances made in the field of MPc-based OTFTs since 2008.

Chloro boron subphthalocyanine and its derivatives: dyes, pigments or somewhere in between?

Nine derivatives of chloro boron subphthalocyanine (Cl-BsubPc, 1) have been synthesized and characterized. Seven dimers of Cl-BsubPc have been synthesized by reaction with biphenol (2a), bisphenol A (2b), bisphenol F (2c), bisphenol O (2d), bisphenol P (2e), bisphenol S (2f) and bisphenol Z (2g). For comparison two monomeric phenoxy- (3a) and 4-methylphenoxy (3b) BsubPcs have also been synthesized. Crystals were grown for dimer 2c, whereas all attempts to grow crystals of the remaining dimers resulted in the formation of molecular glasses or amorphous precipitates. Analysis on the structure of 2c suggests that the rigidity and aromatic nature of the central bisphenolic directs the crystal packing. The solubility of the BsubPc dimers in a variety of common organic solvents was measured and compared to that of Cl-BsubPc (2) and monomers 3a and 3b. We have defined ranges for classifying BsubPc derivatives based on their solubility in these solvents: pigment < or = 1 x 10(-8) M, 1 x 10(-3) M < or = pigment-like > 1 x 10(-8) M, 1 x 10(-2) M < or = dye-like > 1 x 10(-3) M, and dye > 1 x 10(-2) M. From this Cl-BsubPc (1) and compounds 2a, 2b, 2c, 2e and 2g are pigment-like while compounds 2d, 2f, 3a and 3b are dye-like. None are exclusively pigments or dyes. In this first approximation of this dye versus pigment classification we have not considered other processes besides solvation which could be undesirable such as polymorphic changes or Ostwald ripening. We have concluded that derivatization of Cl-BsubPc (1) with bisphenols and phenols can be used to control the solubility of BsubPc derivatives. We have also concluded that Cl-BsubPc (1) should not be considered a dye rather is pigment-like in its solubility.

Bis(tri-n-hexylsilyl oxide) Silicon Phthalocyanine: A Unique Additive in Ternary Bulk Heterojunction Organic Photovoltaic Devices

Previous studies have shown that the use of bis(tri-n-hexylsilyl oxide) silicon phthalocyanine ((3HS)2-SiPc) as an additive in a P3HT:PC61BM cascade ternary bulk heterojunction organic photovoltaic (BHJ OPV) device results in an increase in the short circuit current (J(SC)) and efficiency (η(eff)) of up to 25% and 20%, respectively. The previous studies have attributed the increase in performance to the presence of (3HS)2-SiPc at the BHJ interface. In this study, we explored the molecular characteristics of (3HS)2-SiPc which makes it so effective in increasing the OPV device J(SC) and η(eff. Initially, we synthesized phthalocyanine-based additives using different core elements such as germanium and boron instead of silicon, each having similar frontier orbital energies compared to (3HS)2-SiPc and tested their effect on BHJ OPV device performance. We observed that addition of bis(tri-n-hexylsilyl oxide) germanium phthalocyanine ((3HS)2-GePc) or tri-n-hexylsilyl oxide boron subphthalocyanine (3HS-BsubPc) resulted in a nonstatistically significant increase in JSC and η(eff). Secondly, we kept the silicon phthalocyanine core and substituted the tri-n-hexylsilyl solubilizing groups with pentadecyl phenoxy groups and tested the resulting dye in a BHJ OPV. While an increase in JSC and η(eff) was observed at low (PDP)2-SiPc loadings, the increase was not as significant as (3HS)2-SiPc; therefore, (3HS)2-SiPc is a unique additive. During our study, we observed that (3HS)2-SiPc had an extraordinary tendency to crystallize compared to the other compounds in this study and our general experience. On the basis of this observation, we have offered a hypothesis that when (3HS)2-SiPc migrates to the P3HT:PC61BM interface the reason for its unique performance is not solely due to its frontier orbital energies but also might be due to a high driving force for crystallization.

Liquid triarylamines: the scope and limitations of Piers-Rubinsztajn conditions for obtaining triarylamine-siloxane hybrid materials.

New liquid triarylamine-siloxane hybrid materials are produced using the Piers-Rubinsztajn reaction. Under mild conditions, liquid analogues of conventional and commonly crystalline triarylamines are easily synthesized from readily available or accessible intermediates. Using a diverse selection of triarylamines, we explored the effects of siloxane group and substitution pattern on the physical properties of these materials, and we have demonstrated that relatively large molecular liquids with desirable electrochemical properties can be produced. The interactions between the strongly Lewis acidic catalyst used for this transformation, tris(pentafluorophenyl)borane (BCF), and the Lewis basic triarylamine substrates were studied. Through UV-vis-NIR and (19)F NMR spectroscopy, we have proposed that the catalyst undergoes a reversible redox reaction with the substrates to produce a charge transfer complex. The formation of this charge transfer complex is sensitive to the oxidation potential of the triarylamine and can greatly affect the kinetics of the Piers-Rubinsztajn reaction.

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.

Green-sensitive organic photodetectors with high sensitivity and spectral selectivity using subphthalocyanine derivatives.

Green-sensitive organic photodetectors (OPDs) with high sensitivity and spectral selectivity using boron subphthalocyanine chloride (SubPc) derivatives are reported. The OPDs composed of SubPc and dicyanovinyl terthiophene derivative (DCV3T) demonstrated the highest green-sensitivity with maximum external quantum efficiency (EQE) of 62.6 % at an applied voltage of -5 V, but wide full-width-at-half-maximum (FWHM) of 211 nm. The optimized performance considering spectral selectivity was achieved from the composition of N,N-dimethyl quinacridone (DMQA) and SubPc showing the high specific detectivity (D*) of 2.34 × 10(12) cm Hz(1/2)/W, the EQE value of 60.1% at -5 V, and narrow FWHM of 131 nm. In spite of the sharp absorption property of SubPc with the maximum wavelength (λmax) at 586 nm, the EQE spectrum showed favorable green-sensitivity characterized by smooth waveform with λmax at 560 nm, which is induced from the high reflectance of SubPc centered at 605 nm. The photoresponsivity of the OPD devices was found to be consistent with their absorptance. Optimized DMQA/SubPc device showed the lowest value of blue crosstalk (0.42) and moderate red crosstalk (0.37), suggesting its promising application as a green-sensitive OPD.

Observations regarding the crystal structures of non-halogenated phenoxyboronsubphthalocyanines having para substituents on the phenoxy group

We report the synthesis and systematic description of a series of five para-substituted phenoxy-BsubPcs including their characterization in the crystal state. The nature of the substituents on the phenoxy molecular fragment was chosen so as to vary both the size and electronegativity: specifically with increasingly bulky para-alkyl groups from hydrogen to tert-octyl and a single electronegative substitute (F). Examination of the arrangement of the phenoxy-BsubPcs within single crystals allows us to place each into one of the two categories. The first, which contains all but one of the derivatives, has a repeating motif which is made up of dimers of the BsubPc molecular fragments. The second, containing only the derivative possessing the large tert-octyl substituent, is characterized by the formation of ribbons instead of dimers of the BsubPc fragment. Regardless of motif the arrangement of the BsubPc molecular fragments was found to be convace–concave.

Siloxane−Triarylamine Hybrids: Discrete Room Temperature Liquid Triarylamines via the Piers−Rubinsztajn Reaction

A series of room temperature liquid siloxane-triarylamine hybrids were synthesized using the Piers-Rubinsztajn reaction. These materials displayed well behaved electrochemical oxidation and low T(g)s and were free-flowing liquids. The interaction between the Lewis acidic tris(pentafluorophenyl)borane catalyst and the Lewis basic starting triarylamine substrate was also investigated by steady state UV-vis spectroscopy and (19)F NMR.

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.