NOVELTY - Pyrrolopyrrole derivatives are new.    USE - As semiconducting effective unit in semiconductor devices such as sensor, diode, photodiode, organic field effect transistor, transistor for flexible displays and/or heterojunction solar cell; as a p-type transistor (claimed); and as organic semiconductors.    ADVANTAGE - The compounds are small molecules with improved power conversion efficiency (PCE), high field effect mobility (charge carrier mobility), high on/off current ratio, and low threshold voltage.    DETAILED DESCRIPTION - Pyrrolopyrrole derivatives of formula (I) are new.    R1 and R2=up to 49C aliphatic, cycloaliphatic, cycloaliphatic-aliphatic, aromatic, aromatic-aliphatic, heteroaromatic or heteroaromatic-aliphatic group;    a and d=0-3;    Ar1 and Ar4=a bivalent group of formula phenylene (substituted by -(R5)p) (ia) or thiophene-2,5-diyl (substituted on 3-position by R6 and on 7-position by R7) (ib);    p=0-2;    R5=up to 25C aliphatic hydrocarbon;or    two vicinal R5 together=up to 7C alkylene or alkenylene;    b, c, e and f=1-3;    Ar2, Ar3, Ar5 and Ar6=a bivalent group of formula (ib), thiazol-2,5-diyl (substituted on 4-position by R8) (ic), 4H-cyclopenta(2,1-b;3,4-b')dithiophene-2,6-diyl (substituted on 3-position by R9, di-substituted on 4-position by R10 and R11 and on 5-position by R12) (id), thieno(3,2-b)thiophene-2,5-diyl (substituted on 3-position by R13 and on 6-position by R14) (ie), thieno(2,3-b)thiophene-2,5-diyl (substituted on 3-position by R15, on 4-position by R16) (if), dithieno(3,2-b;2',3'-d)thiophene-2,6-diyl (substituted on 3-position by R17 and on 5-position by R18) (ig), benzo(1,2-b;4,5-b')dithiophene-2,6-diyl (substituted on 3-position by R19, on the phenyl ring by R20 and on 7-position by R21) (ih) or benzo(1,2,5)thiadiazol-4,7-diyl (ij);    R6-R9, R12, R13, R15-R21=hydrogen, 1-25C alkyl, 1-18C alkoxy, 6-24C aryl, 7-25C aralkyl, or heteroaryl;or    R6+R7=up to 25C alkylene or alkenylene which may be both bonded via oxygen and/or sulfur to the thienyl residue;    R10 and R11=H, 1-18C alkyl, 6-24C aryl or heteroaryl;or    R10+R11=oxo or a five or six membered ring, which is optionally substituted by up to 18C aliphatic hydrocarbon group, 1-18C alkoxy or 2-18C alkylenedioxy in both of which carbon atoms which are not adjacent to oxygen may be replaced by oxygen, or 6-24C aryl, 7-25C aralkyl, heteroaryl, 3-12C cycloalkyl or 4-12C cycloalkyl-alkyl;    R3 and R4=phenyl (substituted on 2-position by R22, on 3-position by R23, on 4-position by R24, on 5-position by R26 and on 6-position by R26) (iia), thiophene-2-yl (substituted on 3-position by R28, on 4-position by R27 and on 5-position by R58) (iib), benzo(b)thiophene-2-yl (substituted on 3-position by R29, on 4-position by R30, on 5-position by R31, on 6-position by R32 and on 7-position by R33) (iic), naphtho(2,3-b)thiophene-2-yl (substituted on 3-position by R34, on 4-position by R35, on 5-position by R36, on 6-position by R37, on 7-position by R38, on 8-position by R39 and on 9-position by R40) (iid), naphthalene-1-yl (substituted on 2-position by R41, on 3-position by R42, on 4-position by R43, on 5-position by R44, on 6-position by R45, on 7-position by R46, on 8-position by R47) (iie), naphthalene-2-yl (substituted on 1-position by R41, on 3-position by R42, on 4-position by R43, on 5-position by R44, on 6-position by R45, on 7-position by R46, on 8-position by R47) (iif), anthracene-1-yl (substituted on 2-position by R48, on 3-position by R49, on 4-position by R50, on 5-position by R51, on 6-position by R52, on 7-position by R53, on 8-position by R54, on 9-position by R55 and on 10 position by R56) (iig), anthracene-2-yl (substituted on 1-position by R57, on 3-position by R49, on 4-position by R50, on 5-position by R51, on 6-position by R52, on 7-position by R53, on 8-position by R54, on 9-position by R55 and on 10 position by R56) (iih) or anthracene-9-yl (substituted on 1-position by R57, on 2-position by R48, on 3-position by R49, on 4-position by R50, on 5-position by R52, on 6-position by R53, on 7-position by R54, on 8-position by R55 and on 10 position by R51) (iij);    R22-R26 and R29-R58=H, up to 25C aliphatic hydrocarbon, up to 18C alkoxy or alkenyloxy, halogen, up to 25C cycloaliphatic, cycloaliphatic-aliphatic, aromatic, aromatic-aliphatic, heteroaromatic or heteroaromatic-aliphatic group or a group of formula -C?=C-Pt(P(R)3)2(phenyl) (iiia);    R=up to 12C aliphatic hydrocarbon group;or    two groups R22 to R26 and R29 to R57 which are in the neighborhood of each other, together=up to 8C alkylene or alkenylene, thereby forming a ring;    R27 and R28=H, 1-25C alkyl, 1-18C alkoxy, 6-24C aryl, 7-25C aralkyl, heteroaryl, or group (iiia);or    R27+R28 and R27+R58=up to 25C alkylene or alkenylene which may be both bonded via oxygen and/or sulfur to the thienyl residue.    An INDEPENDENT CLAIM is included for a semiconductor device comprising as a semiconducting effective unit the compound (I).