SYNTHESIS OF CONJUGATED SMALL MOLECULES AND POLYMERS BY A PALLADIUM CATALYZED CYCLOPENTANNULATION STRATEGY – TOWARDS NEW ORGANIC SEMICONDUCTORS

Author

Sambasiva Reddy Bheemireddy, Southern Illinois University CarbondaleFollow

Date of Award

5-1-2017

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Plunkett, Kyle

Abstract

The utility of conjugated small molecules and polymers as organic semiconductors have seen a tremendous growth in research and development in academia as well as industry because of their processability and flexibility advantages in comparison to inorganic semiconductors. The extensive research over the years has produced a large number of p-type (hole conducting) and n-type (electron conducting) semiconductors that can be used to construct organic electronic devices. Of these materials, p-type semiconductors are more established and extensively studied because of the ease of preparation as well as their better general stability in comparison to n-type materials. Despite recent research into the development of n-type materials, fullerene (C60 and C70) and its derivatives are still the predominant materials used as electron acceptors for OPV applications. By taking advantage of the electron accepting behavior of cyclopenta[hi]aceanthrylene fragment of C70, we have designed and synthesized new materials based on cyclopenta-fused polycyclic aromatic hydrocarbons (CP-PAHs). By using a newly developed palladium catalyzed cyclopentannulation methodology, 1,2,6,7- tetraarylcyclopenta[hi]aceanthrylenes were prepared by treating diarylethynylenes with 9,10-dibromoanthracene. Scholl cyclodehydrogenation was used to close the externally fused aryl groups to provide access to contorted 2,7,13,18- tetraalkoxytetrabenzo[f,h,r,t]rubicenes. The contortion provides access to more soluble materials than their planar counterparts but still ii allows significant pi-pi stacking between molecules. Using a modified palladium catalyzed cyclopentannulation polymerization followed by a cyclodehydrogenation reaction, a nonconventional synthesis of CP-PAH embedded ladder polymers was also achieved. These ladder polymers possess broad UV-Vis absorptions and narrow optical gaps of 1.17-1.29 eV. The synthesis of new donor-acceptor copolymers incorporating electron accepting 1,2,6,7- tetra(4-dodecylphenyl)dicyclopenta[cd,jk]pyrene was also achieved. The donor unit was varied between thiophene, bithiophene, and 1,4-diethynyl-2,5-bis((2-octyldodecyl)oxy)-benzene producing polymers with high molecular weights and considerably low band gaps. This newly developed cyclopentannulation method was also used to synthesize a new class of stabilized pentacene derivatives with externally fused five-membered rings. The target compounds were synthesized via chemical manipulation of a partially saturated 6,13-dibromopentacene precursor that can be fully aromatized in a final step via a DDQ mediated dehydrogenation reaction. Photodegradation studies reveal the new 1,2,8,9-tetraphenyldicyclopenta[fg,qr]pentacene derivatives are more photostable than TIPS-pentacene, and possess narrow optical gaps of ~1.2 eV. Because anthradithophene (ADT) is more stable than pentacene while maintaining good electronic properties, the synthesis of cyclopentannulated anthradithiophenes (CP-ADTs) was also explored. Synthesis of a highly contorted ADT analogue was achieved by treating 5,11-dibromo-anthradithiophene with 3,3’-dimethoxy,1,1’-diphenyl acetylene under palladium catalyzed cyclopentannulation conditions followed by Scholl cyclodehydrogenation.