Selective growth of alpha-form zinc phthalocyanine nanowire crystals via the flow rate control of physical vapor transport

Abstract

alpha-Form zinc phthalocyanine (ZnPc), a kinetically favorable form of ZnPc, is an efficient photosensitizer for photodynamic cancer therapy, especially when it is formed into nanowires (NWs), which have high water dispersibility. To take full advantage of this material, it is necessary to selectively grow kinetically favorable alpha-form ZnPc NWs over thermodynamically favorable beta-form ZnPc NWs. The present study reports the selective growth of kinetically favorable alpha-form ZnPc NW crystals by a physical vapor transport method with flow rate control of the carrier gas. The flow rate is key for the dominant growth of alpha-form ZnPc NWs, thus enabling control of the crystal size, which critically affects the stability of ZnPc crystals. The yield of alpha-form ZnPc NWs was over 98% at a flow rate of 2000 sccm of Ar carrier gas. This approach could be applied for various Pc molecules, including copper phthalocyanine (CuPc). Our findings might contribute to the development of novel strategies for the selective growth of high-quality kinetically favorable crystals with a specific structure and provide great opportunities for their various practical applications.