A series of quadrupolar (A-π-D-π-A)
tetra-aryl 1,4-dihydropyrrolo[3,2-b]pyrrole (DHPP)
derivatives synthesized are showcased as
potential organic resistive memory (ORM) devices for the first time.
The experimental observations coupled with density functional theory
(DFT) calculations probe in detail the role of terminal substituent
groups (p-NH2, p-Cl, p-CN, p-NO2, m-NO2) on the optical and electrical properties. Electrochemical
studies reveal that the 3- and 4-dinitro derivatives form an unusual
class of tetra-aryl DHPPs that exhibit intrinsic amphoteric redox
behavior contrary to the literature reports. The bipolar nature within
a single molecule was harnessed to design operational ORMs. Interestingly,
the memory devices fabricated using the structural isomers exhibited
dissimilar memory characteristics. While the p-NO2 derivative displays permanent Write Once Read Many
times (WORM) memory, its meta-counterpart
represents a behavior akin to rewriteable flash memory. The noticeably
higher ON/OFF ratio (∼104) for the p-NO2 derivatives could be ascribed to their matched redox
energy levels with the work function of active electrodes favoring
better charge injection. Rational interpretation of these findings
strongly suggests that the choice and strategic positioning of terminal
substituents can significantly alter the nature of “charge
traps” affecting the device outcome. These encouraging findings
open up a relatively less chartered territory of air stable fused
pyrrole systems that holds great promise for realizing next generation
organic memory devices.
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