Silicon phthalocyanines: synthesis and resurgent applications

The intense far-red absorption and emission features have made silicon phthalocyanines (SiPcs) distinct from the structurally related porphyrin analogues. Unlike most other phthalocyanines, SiPcs possess two additional axial bonds which reduce aggregation in solution and can be synthetically tailored, thereby creating further scope for modulation of optical, chemical and electronic properties. Multiple synthetic strategies have been employed for facile construction of symmetrical or unsymmetrical SiPc variants bearing desired substitutents at the axial and the aromatic ring positions. The overarching motive of this concise review article is to highlight and summarize the key synthetic routes and the fast-emerging applications of SiPcs in photouncaging techniques, photothermal and photoimmunotherapy, photovoltaics, optoelectronics and photocatalysis.