Cancer which is tried to be treated with enormous efforts is still an important health problem [1], [2], [3]. Photodynamic therapy (PDT), a non-invasive photon activated treatment method, has been developed and gained increasing attention for cancer treatment in recent years [4], [5], [6]. PDT is based on photosensitizers and light to produce reactive oxygen species (ROS) to destroy cancer cells [7], [8], [9], [10]. Nevertheless, limited penetration effect of laser the light causes PDT applications to be limited to superficial lesions [11], [12], [13]. Inspired by PDT, sonodynamic therapy (SDT) which uses ultrasound to activate photosensitizers was developed to overcome this problem [14], [15], [16]. Unlike visible light, ultrasound mechanical wave can penetrate a cancer target buried deep in the tissue. Despite SDT overcomes the major limitation of PDT, the appropriate sonosensitizers for clinical applications have not been approved [[15], [17], [18], [19]]. Sono-photodynamic therapy (SPDT) is an alternative treatment that combines photodynamic and sonodynamic therapies. Sensitizers can be excited by both light and ultrasound more effectively than just light or ultrasound [20]. The synergistic energy of light and ultrasound enables a more effective treatment for deeply located tumors by generating mechanical, sonochemical and photochemical events [21], [22], [23], [24]. The key element of SPDT is sensitizer which should have a stable chemical composition, high clearance rate from normal tissues and no significant toxicity and can be activated by both ultrasound and light to produce photochemical and sonochemical activities [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27]. While direct cytotoxic effects due to free-radical oxidation, disruption of the blood supply to the tumor tissue occurs during PDT, physical and physicochemical processes occurs during SDT. Combined exposure of photosensitizers, laser and ultrasonic radiation results in apoptosis and necrosis [28]. Also cell migration is inhibited by combined therapy [29]. Studies in the literature revealed the higher therapeutic effect of SPDT compared to PDT [[30], [31], [32]]. Due to their physicochemical properties phthalocyanines have gained attention and been studied for SPDT applications [11,16,33]. Schiff bases are condensation reactions of a primary amine and carbonyl group. Their physical, chemical properties and biological activities have been investigated so far [[34], [35], [36], [37], [38], [39]].

This paper aims to synthesize novel sono-photo sensitizers with improved singlet oxygen efficiencies. Quinoline and phenantroline derivatives and SiPc have biological activity separately. It is targeted to improve singlet oxygen quantum yield by combining two compounds which have biological activities. For this purpose, two novel di-axially Schiff base substituted silicon (IV) phthalocyanines have been synthesized to investigate their sono-photochemical effects in cancer treatment. Furthermore, the photophysical, photochemical, and sono-photochemical studies were carried out to present the differences in methods to determine singlet oxygen yield.