Materials Chemistry

A Tale of Two Transitions: Unraveling Two Distinct Polymorph Transition Mechanisms in One n-Type Single Crystal for Dynamic Electronics

Authors

Abstract

Cooperativity is used by living systems to circumvent energetic and entropic barriers to yield highly efficient molecular processes. Cooperative structural transitions involve the simultaneous, concerted displacement of molecules in a crystalline material, in stark contrast to the more typical molecule-by-molecule nucleation and growth mechanism often breaking the single crystallinity. Cooperative transitions have acquired much attention in the research community for their low transition barriers, ultrafast kinetics, and structural reversibility. On the other hand, cooperative transitions are rarely observed in molecular crystals and the molecular origin is not well understood. Single crystals of 2-dimensional quinoidal terthiophene (2DQTT-o-B), a high-performance n-type organic semiconductor, demonstrate two thermally-activated, reversible phase transitions with one exhibiting a cooperative mechanism and the second exhibiting a nucleation and growth mechanism. In situ microscopy, single crystal and grazing incidence X-ray diffraction (GIXD), along with Raman spectroscopy suggest a reorientation of the alkyl side chains results in a cooperative transition behavior. On the other hand, the nucleation and growth transition is coincident with both side chain melting and the emergence of new spin-spin interactions between conjugated cores, confirmed through in situ electron paramagnetic resonance spectroscopy (EPR). This is the first observation of biradical interactions directly initiating a structural transition. Through studying these fundamental mechanisms, we establish alkyl chain conformation and disorder as integral to rationally controlling these polymorphic behaviors for novel electronic applications.

Content

Thumbnail image of Davies_Diao_MechanismPaper_NatChem_2021_2.pdf

Supplementary material

Thumbnail image of Davies_Diao_MechanismPaper_NatChem_2021_SI.pdf
Supplementary Information
Supplementary figures and description of Raman peak assignments.
Thumbnail image of Movie_S1_I-II_Heating.mp4
Movie_S1_I-II_Heating
video showing the I-II heating transition under polarized optical microscopy
Thumbnail image of Movie_S2_II-I_Cooling.mp4
Movie_S2_II-I_Cooling
Video showing the II-I cooling transition under polarized optical microscopy
Thumbnail image of Movie_S3_II-III_Heating.mp4
Movie_S3_II-III_Heating
Video showing the II-III Heating transition under polarized optical microscopy
Thumbnail image of Movie_S4_III-II_Cooling.mp4
Movie_S4_III-II_Cooling
Video showing the III-II cooling transition under polarized optical microscopy
Thumbnail image of Movie_S5_II-I_Cooling_CrackFormation.mp4
Movie_S5_II-I_Cooling_CrackFormation
Video showing crack formation during the II-I cooling transition under polarized optical microscopy
Thumbnail image of Movie_S6_Heating_thermosalient.mp4
Movie_S6_Heating_thermosalient
Video showing the thermosalient motion during the I-II transition
Thumbnail image of Movie_S7_GIXD_I-II.mp4
Movie_S7_GIXD_I-II
Video showing the changes in grazing incidence X-ray diffraction pattern during the I-II transition
Thumbnail image of Movie_S8_Quinoidal_1581.mp4
Movie_S8_Quinoidal_1581
Simulation of the vibrational mode calculated in the quinoidal form Raman spectra at 1581 cm^-1
Thumbnail image of Movie_S9_Quinoidal_1584.mp4
Movie_S9_Quinoidal_1584
Simulation of the vibrational mode calculated in the quinoidal form Raman spectra at 1584 cm^-1
Thumbnail image of Movie_S10_Quinoidal_1636.mp4
Movie_S10_Quinoidal_1636
Simulation of the vibrational mode calculated in the quinoidal form Raman spectra at 1636cm^-1
Thumbnail image of Movie_S11_Quinoidal_1878_COstretch.mp4
Movie_S11_Quinoidal_1878_COstretch
Simulation of the vibrational mode calculated in the quinoidal form Raman spectra at 1878 cm^-1
Thumbnail image of Movie_S12_Quinoidal_1610.mp4
Movie_S12_Quinoidal_1610
Simulation of the vibrational mode calculated in the quinoidal form Raman spectra at 1610 cm^-1
Thumbnail image of Movie_S13_GIXD_II-III.mp4
Movie_S13_GIXD_II-III
Video showing the changes in grazing incidence X-ray diffraction pattern during the II-III transition
Thumbnail image of Movie_S14_AromaticNoCyano_1618.mp4
Movie_S14_AromaticNoCyano_1618
Simulation of the vibrational mode calculated in the aromatic form Raman spectra at 1618 cm^-1
Thumbnail image of Movie_S15_AromaticNoCyano_1635.mp4
Movie_S15_AromaticNoCyano_1635
Simulation of the vibrational mode calculated in the aromatic form Raman spectra at 1635 cm^-1