A New Iterative Approach for the Synthesis of Oligo(phenyleneethynediyl) Derivatives and Its Application for the Preparation of FullereneOligo(phenyleneethynediyl) Conjugates as Active Photovoltaic Materials

Disymmetrically substituted oligo(phenyleneethynediyl) (OPE) derivatives were prepared from 2,5‐bis(octyloxy)‐4‐[(triisopropylsilyl)ethynyl]benzaldehyde ( 5 ) by an iterative approach using the following reaction sequence: i ) Corey–Fuchs dibromoolefination, ii ) treatment with an excess of lithium diisopropylamide, and iii ) a metal‐catalyzed cross‐coupling reaction of the resulting terminal alkyne with 2,5‐diiodo‐1,4‐bis(octyloxy)benzene ( 3 ) ( Schemes 2 and 3 ). Reaction of the OPE dimer 8 and trimer 13 thus obtained with N ‐methylglycine and C 60 in refluxing toluene gave the corresponding C 60 OPE conjugates 16 and 17 , respectively ( Scheme 4 ). On the other hand, treatment of the protected terminal alkynes 8 and 13 with Bu 4 N followed by reaction of the resulting 9 and 14 with 4‐iodo‐ N , N ‐dibutylaniline under Sonogashira conditions yielded 10 and 15 , respectively ( Schemes 2 and 3 ). Subsequent treatment with N ‐methylglycine and C 60 in refluxing toluene furnished the C 60 OPE derivatives 18 and 19 ( Scheme 4 ). Compound 9 was also subjected to a Pd‐catalyzed cross‐coupling reaction with 3 to give the centrosymmetrical OPE pentamer 20 ( Scheme 5 ). Subsequent reduction followed by reaction of the resulting diol 21 with acid 22 under esterification conditions led to bis‐malonate 23 . Oxidative coupling of terminal alkyne 14 with the Hay catalyst gave bis‐aldehyde 24 ( Scheme 6 ). Treatment with diisobutylaluminium hydride followed by dicylcohexylcarbodiimide‐mediated esterification with acid 22 gave bis‐malonate 26 . Finally, treatment of bis‐malonates 23 and 26 with C 60 , I 2 , and 1,8‐diazabicylco[5.4.0]undec‐7‐ene (DBU) in toluene afforded the bis[cyclopropafullerenes] 27 and 28 , respectively ( Scheme 7 ). The C 60 derivatives 16 – 19, 27 , and 28 were tested as active materials in photovoltaic devices. Each C 60 OPE conjugate was sandwiched between poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate)‐covered indium tin oxide and aluminium electrodes. Interestingly, the performances of the devices prepared from the N , N ‐dialkylaniline‐terminated derivatives 18 and 19 are significantly improved when compared to those obtained with 16, 17, 27 , and 28 , thus showing that the efficiency of the devices can be significantly improved by increasing the donor ability of the OPE moiety.