Technologies which utilize near-infrared (NIR) (700−1000 nm) and short-wave infrared (1000− 2000 nm) electromagnetic radiation have applications in deep-tissue imaging, telecommunications, and satellite telemetry due to low scattering and decreased background signal in this spectral region. It is therefore necessary to develop materials that absorb light efficiently beyond 1000 nm. Transition dipole moment coupling (e.g., J-aggregation) allows for red-shifted excitonic states and provides a pathway to highly absorptive electronic states in the infrared. We present aggregates of two cyanine dyes whose absorption peaks red-shift dramatically upon aggregation in water from ∼800 to 1000 nm and 1050 nm, respectively, with sheet-like morphologies and high molar absorptivities (ε ≈ 10 5 M −1 cm −1 ). We use Frenkel exciton theory to extend Kasha's model for Jand H-aggregations and describe the excitonic states of two-dimensional aggregates whose slip is controlled by steric hindrance in the assembled structure. A consequence of the increased dimensionality is the phenomenon of an intermediate "I-aggregate", one which red-shifts yet displays spectral signatures of band-edge dark states akin to an H-aggregate. We distinguish between H-, I-, and J-aggregates by showing the relative position of the bright (absorptive) state within the density of states using temperature-dependent spectroscopy. I-aggregates hold potential for applications such as charge injection moieties for semiconductors and donors for energy transfer in NIR and short-wave infrared. Our results can be used to better design chromophores with predictable and tunable aggregation with new photophysical properties.

2014 On montre pour la première fois que des molécules discotiques de benzène-hexa-alkanoates peuvent être étalées en monocouches à un interface eau-air. Les mesures de pression superficielles donnent des résultats très analogues à ceux des films d'acides gras. Le noyau benzénique joue le rôle de la tête polaire grâce à six groupes carboxyliques périphériques, et se met à plat sur l'interface. Les chaines alkanoates jouent le rôle des chaines aliphatiques. Les isothermes de pression permettent une estimation des dimensions moléculaires dans le plan de l'interface. Ces dimensions sont pratiquement identiques à celles déduites des mesures de rayons X dans les phases à colonnes formées par les benzène-hexa-alkanoates (cristaux liquides thermotropes). Ces expériences permettent de réfuter l'interprétation de la transition liquide expansé-liquide condensé comme une transition du second ordre entre une phase isotrope et une phase cristal liquide nématique. Abstract. 2014 The possibility of forming Langmuir monolayers with disc-like molecules of benzene-hexa-alkanoates has been investigated for the first time. Surface pressure measurements show that these monolayers behave in many respects as the well-known films of fatty acids. The benzene ring plays the role of the polar head group while the alkanoates chains are the long aliphatic tails. Molecular dimensions can be derived from the surface pressureconcentration isotherms. The results indicate that the benzene rings lie flat at the interface. The projection of the molecular diameter onto the interface is practically identical to the lattice spacing measured in the liquid-crystalline columnar mesophases formed by benzene-hexa-alkanoates in bulk. These experiments allow to refute the interpretation of the liquid expanded-liquid condensed transition in terms of a second order isotropic ~ nematic phase transition, as recently proposed by several theoretical groups.

Technologies which utilize near-infrared (700 – 1000 nm) and short-wave infrared (1000 – 2000 nm) electromagnetic radiation have applications in deep-tissue imaging, telecommunications and satellite telemetry due to low scattering and decreased background signal in this spectral region. It is therefore necessary to develop materials that absorb light efficiently beyond 1000 nm. Transition dipole moment coupling (e.g. J-aggregation) allows for redshifted excitonic states and provides a pathway to highly absorptive electronic states in the infrared. We present aggregates of two cyanine dyes whose absorption peaks redshift dramatically upon aggregation in water from ~800 nm to 1000 nm and 1050 nm respectively with sheet-like morphologies and high molar absorptivities (e ~ 10⁵M^-1cm^-1). We use Frenkel exciton theory to extend Kasha’s model for J and H aggregation and describe the excitonic states of 2-dimensional aggregates whose slip is controlled by steric hindrance in the assembled structure. A consequence of the increased dimensionality is the phenomenon of an intermediate “I-aggregate”, one which redshifts yet displays spectral signatures of band-edge dark states akin to an H-aggregate. We distinguish between H-, I- and J-aggregates by showing the relative position of the bright (absorptive) state within the density of states using temperature dependent spectroscopy. I-aggregates hold potential for applications as charge injection moieties for semiconductors and donors for energy transfer in NIR and SWIR. Our results can be used to better design chromophores with predictable and tunable aggregation with new photophysical properties.

Technologies which utilize near-infrared (700 – 1000 nm) and short-wave infrared (1000 – 2000 nm) electromagnetic radiation have applications in deep-tissue imaging, telecommunications and satellite telemetry due to low scattering and decreased background signal in this spectral region. It is therefore necessary to develop materials that absorb light efficiently beyond 1000 nm. Transition dipole moment coupling (e.g. J-aggregation) allows for redshifted excitonic states and provides a pathway to highly absorptive electronic states in the infrared. We present aggregates of two cyanine dyes whose absorption peaks redshift dramatically upon aggregation in water from ~800 nm to 1000 nm and 1050 nm respectively with sheet-like morphologies and high molar absorptivities (e ~ 10⁵M^-1cm^-1). We use Frenkel exciton theory to extend Kasha’s model for J and H aggregation and describe the excitonic states of 2-dimensional aggregates whose slip is controlled by steric hindrance in the assembled structure. A consequence of the increased dimensionality is the phenomenon of an intermediate “I-aggregate”, one which redshifts yet displays spectral signatures of band-edge dark states akin to an H-aggregate. We distinguish between H-, I- and J-aggregates by showing the relative position of the bright (absorptive) state within the density of states using temperature dependent spectroscopy. I-aggregates hold potential for applications as charge injection moieties for semiconductors and donors for energy transfer in NIR and SWIR. Our results can be used to better design chromophores with predictable and tunable aggregation with new photophysical properties.

Technologies which utilize near-infrared (700 – 1000 nm) and short-wave infrared (1000 – 2000 nm) electromagnetic radiation have applications in deep-tissue imaging, telecommunications and satellite telemetry due to low scattering and decreased background signal in this spectral region. However, there are few molecular species, which absorb efficiently beyond 1000 nm. Transition dipole moment coupling (e.g. J-aggregation) allows for redshifted excitonic states and provides a pathway to highly absorptive electronic states in the infrared. We present aggregates of two cyanine dyes whose absorption peaks redshift dramatically upon aggregation in water from ~ 800 nm to 1000 nm and 1050 nm with sheet-like morphologies and high molar absorptivities (e ~ 10⁵M^-1cm^-1). To describe this phenomenology, we extend Kasha’s model for J- and H-aggregation to describe the excitonic states of <i> 2-dimensional aggregates</i> whose slip is controlled by steric hindrance in the assembled structure. A consequence of the increased dimensionality is the phenomenon of an <i>intermediate </i>“I-aggregate”, one which redshifts yet displays spectral signatures of band-edge dark states akin to an H-aggregate. We distinguish between H-, I- and J-aggregates by showing the relative position of the bright (absorptive) state within the density of states using temperature dependent spectroscopy. Our results can be used to better design chromophores with predictable and tunable aggregation with new photophysical properties.