ISIS Neutron and Muon Source Data Journal

Molecular dynamics in an organic semiconductor glass

Abstract: TPD (N,N'-bis(methylphenyl)-N,N'-diphenylbiphenyl-4,4'-diamine) is an organic semiconductor that forms both conventional and ultrastable molecular glasses with applications in OLEDs and flat panel displays. Understanding molecular-level dynamics in TPD glasses is essential for optimizing device performance, yet the relationship between local motions and macroscopic glass properties remains poorly understood. LF-muSR measurements on glassy TPD at ISIS reveal a biexponential spin-lattice relaxation with fast and slow components whose rates show no discontinuity at T_g, in striking contrast to polymer glasses, suggesting that phenyl ring dynamics (gamma relaxation) are decoupled from the cooperative backbone motion driving T_g (alpha relaxation) in molecular glasses. Below T_g, the slow relaxation rate follows an anomalous T^0.35 power law, hypothesized to arise from a broad distribution of local dynamical processes characteristic of the disordered glassy state. We request 2 days on EMU to: (1) confirm the biexponential components arise from muoniated cyclohexadienyl radicals via field-dependent repolarization measurements at 350 K; and (2) perform LF- and TF-muSR on crystalline TPD from 1.5 to 300 K to determine whether the T^0.35 power law is a signature of glassy disorder or reflects local intramolecular dynamics present in both phases.

Principal Investigator: Dr Iain McKenzie
Local Contact: Dr Stephen Cottrell

DOI: 10.5286/ISIS.E.RB2620181

ISIS Experiment Number: RB2620181

Publisher: STFC ISIS Neutron and Muon Source

Data format: RAW/Nexus
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Data Citation

The recommended format for citing this dataset in a research publication is as:
[author], [date], [title], [publisher], [doi]

For Example:
Dr Iain McKenzie et al; (2026): Molecular dynamics in an organic semiconductor glass, STFC ISIS Neutron and Muon Source, https://doi.org/10.5286/ISIS.E.RB2620181

Data is released under the CC-BY-4.0 license.