Optimization of the physical and electronic properties of organic semiconductors is a key step in improving the performance of organic light emitting diodes, organic photovoltaics, organic field effect transistors, and other electronic devices. Separate tuning of the physical and electronic properties of these organic semiconductors can be achieved by the hybridization of organo-silicon structures (silicones, siloxanes, silsesquioxanes) with organic semiconductors. Common chemical means to achieve this hybridization are summarized while a large range of literature examples are covered to demonstrate the range and flexibility of this synthetic strategy.

Organic photovoltaics (OPVs) have experienced continued interest over the last 25 years as a viable technology for the generation of power. Phthalocyanines are among the oldest commercial dyes and have been utilized in some of the earliest examples of OPVs. In recent years, the use of boron subphthalocyanines (BsubPcs) and silicon phthalocyanines (SiPcs) has attracted a flurry of interest with some examples of fullerene‐free devices reaching power conversion efficiencies >8 %. Unlike other more common divalent phthalocyanines such as copper or zinc, BsubPcs and SiPcs contain additional axial groups that can easily be functionalized without significantly affecting the optoelectronic properties of the macrocycle. This handle facilitates our ability to tune the solid‐state arrangement and other physical characteristics such as solubility ultimately giving us the ability to improve the thin film processing and final device performance. This review covers recent studies on the development of BsubPcs and SiPcs for use as active materials in organic photovoltaics.

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 (1) and monomers 3a and 3b. We have defined ranges for classifying BsubPc derivatives based on their solubility in these solvents: pigment ≤ 1 × 10⁻⁸ M, 1 × 10⁻³ M ≤ pigment-like > 1 × 10⁻⁸ M, 1 × 10⁻² M ≤ dye-like > 1 × 10⁻³ M, and dye > 1 × 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.

The optical characterisation and device functionality for a series of axially modified silicon phthalocyanines (SiPcs) as dopant red emitters in solution-processed and vapour-deposited organic light-emitting diodes (OLEDs) is presented.