Progress on the Development of Boron Subphthalocyanines (BsubPcs) and Subnaphthalocyanines (BsubNcs) Including Hybrids and Their Sustainability
Authors: Bender Timothy P , Francesca Farac Nina , Zigelstein Rachel , Wadden Joseph 
Published: August 2024

Our group focuses on molecular design, synthetic methods and in-depth characterization of boron subphthalocyanines (BsubPcs) and subnaphthalocyanines (BsubNcs)[1] to apply them to organic electronics.[2] BsubPcs, BsubNcs and their hybrids called Bsub(Pc3-p-Ncp) are macrocycles with central boron atom and are p-conjugated macrocycles. Our focal point balances between the basic and applied chemistry, chemical engineering and their in-depth physical properties (electrochemistry included). Once materials are developed, we merge them into organic electronics for application into organic light emitting diodes (OLEDs) and organic photovoltaics (OPVs)/organic solar cells (OSCs).

For this presentation, all points above will be factored in and I will focus on our progress on the development of hybrids, and mixed alloys and none mixed alloys of BsubNcs,.

Regarding hybrids, they are a mixture of BsubPcs and BsubNcs, we named as X-RnBsub(Pc3-p-Ncp) – ‘p’ being the numbers of the substitutions; they were formed via reaction of BCl3 and a statistical distribution of phthalonitrile and 2,3-dicyanonaphthalene; X the axial substituent, Rn the number of peripheral substitutions, Pcp the number of 6 p-conjugated bonds, Ncp the number of 10 p-conjugated bonds (Figure).[3] We found that X-RnBsub(Pc1-Nc2) have low photostability, therefore, we developed a ‘statistical’ synthetic methodology to target X-RnBsub(Pc2-Nc1)s, and therefore could be purified to enable physical characterization. Their absorption spectra are as wide if BsubPc+BsubNc was mixed together, therefore, has potential to harvest a larger scope of photons for OPVs or to achieved FRET transfer from a host to emit via OLED. We also confirmed their electrochemical oxidation and reduction stability and their photoluminescence.

More recently, we developed a new methodology called ‘steric hinderance’ to have even a higher yield of the X-RnBsub(Pc3-p-Ncp) hybrids, and the achievement was also based on computational modelling. I will also outline this approach.

In the past as we have shown that BsubNcs end up being a mixed alloyed composition with random bay-position halogenation that is formed during the reaction of BCl3 with 2,3-dicyanonaphthalene at temperature.[4] The random bay-position halogenation has been shown to be impactful in a positive way within OPV devices, negative within OLED devices and also has electrochemical variations. Ongoing, given it is random halogenation, and some of the positive outcomes, this justifies considering additional mixed alloyed compositions.

We have recently been able to develop a separation method for the mixed alloyed BsubNc compositions and acquired data to show the impact of the percentage/number of bay-position halogens, chlorine and bromine included, on the electrochemical potentials and the photoluminescence.[5] We have also applied a computational model to look at the relative impact of the random bay-position halogenation on the electronics.[6] We have found that the frequency of halogenation has a larger impact on the predicted HOMO/LUMO energy levels than does the random halogen positioning around the bay-positions of the BsubNcs. As this computational data is therefore comparable to the acquired electrochemical data.

I will also present a new synthetic methodology to avoid the random bay-position halogenation of the associated BsubNcs. We also have recently within these semesters developed alternative chemistry to more tune the mixed alloys of the BsubNcs. This will also be a part of the presentation.

We have also recently developed an AI-ML method to further accelerate the BsubNc development. The focal point of this approach was to have bay-position substitutions to then not have any random bay-position halogenation of the BsubNcs. So, these current and upcoming outcomes will also be a part of the presentations.

For this presentation, I will also be outlining the sustainability of these great macrocyclic compounds.

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Figure 1