Columnar Mesomorphism of Board-Shaped Perylene, Diketopyrrolopyrrole, Isoindigo, Indigo, and Quinoxalino-Phenanthrophenazine Dyes.

The properties of organic dyes depend as much on their intermolecular interactions as on their molecular structure. While it is generally predictable what supramolecular structure would be ideal for a specific application, the generation of specific supramolecular structures by molecular design and suitable processing methods remains to be a challenge. A versatile approach to different supramolecular structures has been the application of mesomorphism in conjunction with alignment techniques and self-assembly at interfaces. Reviewed here is the columnar mesomorphism of board-shaped dyes perylene, indigo, isoindigo, diketopyrrolopyrrole, and quinoxalinophenanthrophenazine. They generate a larger number of different supramolecular structures than conventional disc-shaped (discotic) mesogens because of their non-circular shape and directional intermolecular interactions. The mesomorphism of all but the perylene derivatives is systematically and comprehensively covered for the first time.

Self-Assembly of Board-Shaped Diketopyrrolopyrrole and Isoindigo Mesogens into Columnar π-π Stacks.

Diketopyrrolopyrrole and isoindigo are commercially important dyes that have recently found broad application as electron acceptor and light-absorbing groups in organic semiconductors. Their self-assembly into specific supramolecular structures to control optoelectronic properties has been hampered by limited options for substitution and their high propensity for crystallization. Reported here is a molecular design that directs self-assembly into previously elusive columnar mesophases of π-π stacking cores. Although attachment of bis(trisoctyloxyphenyl)-1,3,5-triazine groups to both ends of diketopyrrolopyrrole-thiophene and isoindigo cores generated mesomorphic dyes of similar overall shapes and dimensions, distinct differences in their mesomorphism and optoelectronic properties were observed.

Structural awareness mitigates the effect of delay in human causal learning.

Many studies have demonstrated that reinforcement delays exert a detrimental influence on human judgments of causality. In a free-operant procedure, the trial structure is usually only implicit, and delays are typically manipulated via trial duration, with longer trials tending to produce both longer experienced delays and also lower objective contingencies. If, however, a learner can become aware of this trial structure, this may mitigate the effects of delay on causal judgments. Here we tested this "structural-awareness" hypothesis by manipulating whether response-outcome contingencies were clearly identifiable as such, providing structural information in real time using an auditory tone to delineate consecutive trials. A first experiment demonstrated that providing cues to indicate trial structure, but without an explicit indication of their meaning, significantly increased the accuracy of causal judgments in the presence of delays. This effect was not mediated by changes in response frequency or timing, and a second experiment demonstrated that it cannot be attributed to the alternative explanation of enhanced outcome salience. In a third experiment, making trial structure explicit and unambiguous, by telling participants that the tones indicated trial structure, completely abolished the effect of delays. We concluded that, with sufficient information, a continuous stream of causes and effects can be perceived as a series of discrete trials, the contingency nature of the input may be exploited, and the effects of delay may be eliminated. These results have important implications for human contingency learning and in the characterization of temporal influences on causal inference.