Entanglement of states is one of the most surprising and counter-intuitive consequences of quantum mechanics, with potent applications in cryptography and computing. In organic materials, one particularly significant manifestation is the spin-entangled triplet-pair state, which mediates the spin-conserving fission of one spin-0 singlet exciton into two spin-1 triplet excitons. Despite long theoretical and experimental exploration, the nature of the triplet-pair state and inter-triplet interactions have proved elusive. Here we use a range of organic semiconductors that undergo singlet exciton fission to reveal the photophysical properties of entangled triplet-pair states. We find that the triplet pair is bound with respect to free triplets with an energy that is largely material independent (∼30 meV). During its lifetime, the component triplets behave cooperatively as a singlet and emit light through a Herzberg–Teller-type mechanism, resulting in vibronically structured photoluminescence. In photovoltaic blends, charge transfer can occur from the bound triplet pairs with >100% photon-to-charge conversion efficiency.

Polymers are widely used as insulators in electronic devices. Low dielectric constant polymers are desirable since this lowers the potential for unintentional crosstalk and inductive coupling between conductors. Attempts to photopattern a low dielectric constant polymer, poly(5-hexyl-2-norbornene) (poly(1)), with a bis(azide) were unsuccessful. Incorporation of butenyl pendent groups improved patterning, but the dielectric constant of the cross-linked film was relatively high (2.60). A difunctional bis(diazirine) (compound 4) was synthesized and characterized by NMR and MS. Compound 4 rendered unreactive, aliphatic cycloolefin polymers such as poly(1) photopatternable, yielding negative tone patterns with good resolution. The dielectric constant of films cross-linked with compound 4 was substantially lower than the films cross-linked with bis(azide) (2.09 for poly(1)).

In solution‐processable small molecule semiconductors, the extent of charge carrier wavefunction localization induced by dynamic disorder can be probed spectroscopically as a function of temperature using charge modulation spectroscopy (CMS). Here, it is shown based on combined field‐effect transistor and CMS measurements as a function of temperature that in certain molecular semiconductors, such as solution‐processible pentacene, charge carriers become trapped at low temperatures in environments in which the charges become highly localized on individual molecules, while in some other molecules the charge carrier wavefunction can retain a degree of delocalization similar to what is present at room temperature. The experimental approach sheds new insight into the nature of shallow charge traps in these materials and allows identifying molecular systems in which intrinsic transport properties could, in principle, be observed at low temperatures if other transport bottlenecks associated with grain boundaries or contacts could be removed.

The channel temperature (Tch) of solution‐processed 6,13‐bis(triisopropylsilylethynyl)‐pentacene (TIPS pentacene) thin film transistors (TFTs) is closely monitored in real time during current–voltage (I–V) measurements carried out in a He exchange gas cryostat at various base temperatures (Tb) between 300 K and 20 K. This is done using a platinum (Pt) resistance temperature sensor embedded within the transistor channel. Under large gate (Vg) and source‐drain (Vds) voltage biases, an increase in Tch is observed, the magnitude of which depends on the thermal conductivity of the substrate. The increase in Tch is associated with a simultaneous increase in the transistor drain current (Id) and becomes particularly pronounced at cryogenic Tb. These experimental observations are rationalized using a 1D theoretical model and are attributed to current‐induced Joule heating. However, even though the heating of the channel unquestionably plays an important role, the corresponding amount of increase in Id at cryogenic Tb and large voltage biases cannot be fully accounted for unless at low temperatures μTIPS is enhanced in the presence of strong electrical fields. Therefore it is concluded that the I–V characteristics of TIPS pentacene TFTs at low Tb and large voltage biases are a result of a complex interplay between current‐induced Joule heating and electrical field effects.