transition metal complexes have been developed due to their easy access, and promising photoredox properties. They have been widely used in a large range of applications from water splitting, solar energy storage, to photovoltaics and organic redox transformation reactions. [2] Nevertheless, there are still intrinsic drawbacks associated with these rather homogeneous metal complex systems, for example, high cost, toxicity of the rare metals, and limited availability in nature. From this standpoint, transition metalfree photocatalysts with light-absorbing properties have attracted much attention recently. Indeed, the class of organic dyes such as fluorescein, eosin Y, nile red, or rhodamine B have been successfully employed in photoredox catalysis in the last decades. [3] However, a common disadvantage of the organic dyes as molecular catalysts is, similar to the transition metal complexes, that they easily suffer from the solvolytic attack during the reaction cycle. The so-called photobleaching effect can be troublesome for catalyst recycling and long-term usage. It is therefore necessary to design new transition metal-free, stable, and heterogeneous photocatalysts with stability and easy separation and recovery.Traditional metal oxides semiconductors, especially those containing abundant metals are inexpensive, environmentally friendly heterogeneous photocatalysts. [4] Among them, titanium dioxide (TiO 2 ) has been intensely investigated and applied as photocatalyst in a wide range of applications owning to its low cost, high photo-and chemical stability, large availability, biological inertia, etc. However, the fact that TiO 2 can only be activated under UV light (below 380 nm) caused by its wide energy band gap (3.2 eV). This limits its exploitation under the full range of the sunlight. To note, the visible range accounts about 44% of the total solar energy, while the UV light only being about 4%. [5] Different strategies have been developed to improve the sunlight utilization efficiency and the photocatalytic activity of TiO 2 . Several studies have reported such as doping TiO 2 with other metals as Cu, Co, Ni, Cr, Mn, Fe, Ru, Au, Ag, Pt, etc., [6] or with nonmetal such as C, S, F, and I, [7] or co-doping with two different elements. [8] However, these methods still have certain drawbacks such as the thermal instability and the high cost of the dopants. [9] Recently, organic dye-sensitized TiO 2 -based materials have also been investigated and used as photocatalyst for organic photoredox reactions due to their absorption range in the visible area of the solar spectrum and enhanced electronic properties. [10] Nevertheless, the usually weak bonds between TiO 2The search for heterogeneous, visible light-active, transition metal-free, stable, and reusable photocatalysts for organic photoredox reactions remains a challenge for the chemists. Here, this study reports on a series of hybrid photocatalysts consisting of conjugated microporous polymer-based organic semiconductors with immobilized TiO 2 nanoparticles...
