Enlightening the future: AIEgen-integrated phthalocyanines and subphthalocyanines for next-generation functional materials

Abstract

Phthalocyanines and subphthalocyanines have received immense attention owing to their structural versatility and wideranging applications. In particular, the photophysical properties of phthalocyanines can be readily tuned by varying the axial and peripheral substituents, as well as the central metal atom. However, the practical use of phthalocyanines and subphthalocyanines is mainly restricted by their characteristic hydrophobicity and strong aggregation in aqueous environments. This leads to aggregation-caused quenching (ACQ) of photoluminescence, resulting in short-lived photoexcited states and, consequently, low photoluminescence and singlet quantum yields in the aggregated state. To overcome these issues, aggregation-induced emission luminogens (AIEgens), such as tetraphenylethylene and triphenylamine entities, have been integrated into the phthalocyanine and subphthalocyanine frameworks. It has been found that the integration of such AIEgens into the frameworks of phthalocyanines and subphthalocyanines enhances photoluminescence due to restricted intramolecular motions, thereby efficiently converting ACQ-type phthalocyanines and subphthalocyanines into AIE-type materials. Moreover, the unique cone-shaped and π-conjugated structure of subphthalocyanines enables efficient fluorescence resonance energy transfer when combined with AIE-active groups, further enhancing their emission properties. Considering the promising applications of phthalocyanines and subphthalocyanines with AIEgens, in this review, we comprehensively discuss their reported AIE properties and establish their structure-activity relationships to further advance the applications of AIEgen-conjugated phthalocyanines and subphthalocyanines. To the best of our knowledge, no review to date has addressed the importance of phthalocyanines and subphthalocyanines containing AIEgens.