Polymorphic
Phase-Dependent Optical and Electrical
Properties of a Diketopyrrolopyrrole-Based Small Molecule
Shabi Thankaraj Salammal
Zhongqiang Zhang
Jiehuan Chen
Basab Chattopadhyay
Jiake Wu
Lei Fu
Congcheng Fan
Hongzheng Chen
10.1021/acsami.6b05084.s001
https://acs.figshare.com/articles/journal_contribution/Polymorphic_Phase-Dependent_Optical_and_Electrical_Properties_of_a_Diketopyrrolopyrrole-Based_Small_Molecule/3507224
Four different polymorphic conformations
of diethyl 5,5′-[5,5′-[2,5-bis(2-ethylhexyl)-3,6-dioxo-2,3,5,6-tetrahydropyrrolo[3,4-<i>c</i>]pyrrole-1,4-diyl]bis(thiophene-5,2-diyl)]difuran-2-carboxylate
(DPP-(CF)<sub>2</sub>), namely, DPP-(CF)<sub>2</sub>-α, DPP-(CF)<sub>2</sub>-β, DPP-(CF)<sub>2</sub>-γ, and DPP-(CF)<sub>2</sub>-ω, were identified from X-ray diffraction analysis conducted
on their thin films and single crystals. Highly crystalline and well-textured
thin films of these four polymorphs were successfully prepared via
postgrowth solvent vapor and thermal annealing treatments to investigate
the polymorphic phase-dependent optical and electrical properties
of DPP-(CF)<sub>2</sub>. Interestingly, during the phase transition
from DPP-(CF)<sub>2</sub>-α to DPP-(CF)<sub>2</sub>-ω,
the optical band gap decreases from 1.75 to 1.5 eV because of the
enhanced π–π interaction between the neighboring
molecules. Except for DPP-(CF)<sub>2</sub>-γ, the other three
phases show ambipolar charge transport. Although DPP-(CF)<sub>2</sub>-β and DPP-(CF)<sub>2</sub>-γ exhibit a similar way of
packing, a small increment in the π–π-stacking
distance (0.006 Å) and twist conformation of the grafted electron-donating
moieties of DPP-(CF)<sub>2</sub>-γ are found to reduce its hole
mobility.
2016-07-19 00:00:00
twist conformation
band gap decreases
phase transition
phases show ambipolar charge transport
hole mobility
Electrical Properties
DPP
polymorphic conformations
1.5 eV
annealing treatments