Indaceno derivatives as organic semiconductors

A monomer of formula VI

• R5—Ar1—U—Ar2—R6 VI
• wherein U is a unit of formula I
• wherein
• X1 and X2 are independently of each other O, S, Se, Te or CH═CH,
• R1 and R2 independently of each other, and on each occurrence identically or differently, denote H, straight-chain, branched or cyclic alkyl, with 1 to 30 C atoms, in which one or more non-adjacent C atoms are optionally replaced by —O—, —S—, —NR0—, —SiR0R00—, —CY1═CY2— or —C≡C— in such a manner that O and/or S atoms are not linked directly to one another, and in which one or more H atoms are optionally replaced by F, Cl, Br, or I, or R1 and R2, independently of each other, and on each occurrence identically or differently, denote aryl, heteroaryl, aryloxy or heteroaryloxy with 4 to 20 ring atoms which is optionally substituted, or R1 and R2 together form an alicyclic group with 1 to 20 C atoms, which is optionally fluorinated or alkylated,
• Y1 and Y2 are independently of each other H, F, Cl or CN,
• R0 and R00 are independently of each other H or optionally substituted C1-40 carbyl or hydrocarbyl, Ar1, Ar2 aryl or heteroaryl that is different from U, and is optionally substituted, optionally by one or more groups RS, R5 and R6 are independently of each other, H, F, Br, Cl, I, —CH2Cl, —CHO, —CRa═CRb2, —SiRaRbRc, —SiRaX′X″, —SiRaRbX′, —SnRaRbRc, —BRaRb, —B(ORa)(ORc), —B(OH)2, —O—SO2—Ra, —C≡CH, —C≡C—SiRa3, —ZnX′, —Sn(Z4)3, an endcap group, or P-Sp-, wherein P is a polymerizable or crosslinkable group, Sp is a spacer group or a singlebond, X′ and X″ denote halogen, Ra, Rb and Rc independently of each other denote H or alkyl with 1 to 20 C atoms, and two of Ra, Rb and Rc may also form an aliphatic ring together with the hetero atom to which they are attached, and Z4 is alkyl or aryl, each being optionally substituted, RS is on each occurrence identically or differently F, Br, Cl, —CN, —NC, —NCO, —NCS, —OCN, —SCN, —C(O)NR0R00, —C(O)X0, —C(O)R0, —NH2, —NR0R00, —SH, —SR0, —SO3H, —SO2R0, —OH, —NO2, —CF3, —SF5, optionally substituted silyl, carbyl or hydrocarbyl with 1 to 40 C atoms that is optionally substituted and optionally comprises one or more hetero atoms, or P-Sp-, and at least one of R5 and R6 is different from H, and * represents a linkage to an adjacent unit or group.