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.

A tetraphenylcyclopentadiene based multifunctional, solution processable, fluorescent, ultramicroporous polymer exhibiting high hydrogen uptake was employed for encapsulation of dyes to obtain enhanced white light emission in solution, nanoparticles, gel and transparent thin film. Hybrid nanoparticles showed a quantum yield of 35% with a high color rendering index.

Fax: +91 (0)755 409 2392; Tel: +91 (0)755 669 2378. †Electronic Supplementary Information (ESI) available: [Details of characterizations of the polymer, molecular structures of the analytes, limits of detection, solid-state contact mode detection of nitroanilines, EPR and computational investigations.]. SeeA solution processable conjugated porous organic polymer (POP) based on tetraphenyl-5,5dioctylcyclopentadiene (TPDC-DB) was employed for nitroaromatics sensing by amplified fluorescence quenching. A comprehensive investigation was carried out using a set of 30 closely related analytes such as nitrophenols, nitrotoluenes, nitroanilines, nitobenzenes, quinones etc. Nitroanilines were found to be the most efficient quenchers in contrast to the extensively studied picric acid, which is unprecedented among POPs. Rigorous spectroscopic investigations including UV-Vis absorption, steady-state and time-resolved fluorescence, electron paramagnetic resonance coupled with computational studies provided new insight into the underlying photophysical phenomenon of fluorescence quenching. The Stern-Volmer plots were analyzed employing sphere of action model. It was observed that the electron-deficient nature of the nitroaromatics is not the sole governing factor responsible for fluorescence quenching. Naked eye detection of nitroanilines by TPDC-DB was also demonstrated. Detection limits for p-nitroaniline were found to be extremely low, 455 ppb in solution and ~ 1.8 ng cm -2 in contact mode. Scheme 1. Fabrication of porous organic polymer TPDC-DB by Sonogashira cross coupling between tetrakis(4-bromophenyl)-5,5dioctylcyclopentadiene and 1,4-diethynylbenzene.

Despite broad applications in imaging, energy conversion, and telecommunications, few nanoscale moieties emit light efficiently in the shortwave infrared (SWIR, 1000–2000 nm or 1.24–0.62 eV). We report quantum-confined mercury chalcogenide (HgX, where X = Se or Te) nanoplatelets (NPLs) can be induced to emit bright (QY > 30%) and tunable (900–1500+ nm) infrared emission from attached quantum dot (QD) “defect” states. We demonstrate near unity energy transfer from NPL to these QDs, which completely quench NPL emission and emit with a high QY through the SWIR. This QD defect emission is kinetically tunable, enabling controlled midgap emission from NPLs. Spectrally resolved photoluminescence demonstrates energy-dependent lifetimes, with radiative rates 10–20 times faster than those of their PbX analogues in the same spectral window. Coupled with their high quantum yield, midgap emission HgX dots on HgX NPLs provide a potential platform for novel optoelectronics in the SWIR.

Molecular aggregates with long-range excitonic couplings have drastically different photophysical properties compared to their monomer counterparts. From Kasha's model for one-dimensional systems, positive or negative excitonic couplings lead to blue or red-shifted optical spectra with respect to the monomers, labeled H-and J-aggregates, respectively. The overall excitonic couplings in higher dimensional systems are much more complicated and cannot be simply classified from their spectral shifts alone. Here, we provide a unified classification for extended 2D aggregates using temperature dependent peak shifts, thermal broadening, and quantum yields. We discuss the examples of six 2D aggregates with J-like absorption spectra but quite drastic changes in quantum yields and superradiance. We find the origin of the differences is, in fact, a different excitonic band structure where the bright state is lower energy than the monomer but still away from the band edge. We call this an “I-aggregate.” Our results provide a description of the complex excitonic behaviors that cannot be explained solely on Kasha's model. Furthermore, such properties can be tuned with the packing geometries within the aggregates providing supramolecular pathways for controlling them. This will allow for precise optimizations of aggregate properties in their applications across the areas of optoelectronics, photonics, excitonic energy transfer, and shortwave infrared technologies.