Ishita Neogi

Amorphous Host Materials Based on Tröger’s Base Scaffold for Application in Phosphorescent Organic Light-Emitting Diodes

Trögers bases (TBs) functionalized with carbazoles (TB-Czs) and phosphine oxides (TB-POs) were designed and synthesized as host materials for application in phosphorescent organic light-emitting diodes. The TB scaffold is shown to impart thermal stability with high Tg values (171-211 °C) as well as high triplet energies in the range of 2.9-3.0 eV. With a limited experimentation of the devices, it is shown that the TBs doped with a green phosphor, namely, Ir(ppy)3, permit impressive external efficiencies on the order of ca. 16% with a high brightness of ca. 3000-4000 cd/m2. Better device performance results are demonstrated by a small structural manipulation of the TB scaffold involving substitution of methyl groups in the core scaffold.

Tunable room-temperature spin-selective optical Stark effect in solution-processed layered halide perovskites

A new spin on perovskites untwined: Ultrafast optical switching and tuning of spin-energy states in layered halide perovskites. Ultrafast spin manipulation for opto–spin logic applications requires material systems that have strong spin-selective light-matter interaction. Conventional inorganic semiconductor nanostructures [for example, epitaxial II to VI quantum dots and III to V multiple quantum wells (MQWs)] are considered forerunners but encounter challenges such as lattice matching and cryogenic cooling requirements. Two-dimensional halide perovskite semiconductors, combining intrinsic tunable MQW structures and large oscillator strengths with facile solution processability, can offer breakthroughs in this area. We demonstrate novel room-temperature, strong ultrafast spin-selective optical Stark effect in solution-processed (C6H4FC2H4NH3)2PbI4 perovskite thin films. Exciton spin states are selectively tuned by ~6.3 meV using circularly polarized optical pulses without any external photonic cavity (that is, corresponding to a Rabi energy of ~55 meV and equivalent to applying a 70 T magnetic field), which is much larger than any conventional system. The facile halide and organic replacement in these perovskites affords control of the dielectric confinement and thus presents a straightforward strategy for tuning light-matter coupling strength.

Organic amorphous hole-transporting materials based on Tröger's Base: alternatives to NPB

Trogers Base (TB) scaffold has been exploited to create two novel amorphous hole-transporting materials (HTMs), i.e., TB1 and TB2, with high Tgs (152–156 °C) as alternatives to the popular NPB (Tg ∼ 95 °C). The hole-transporting properties of both TB1–2 are shown to be comparable to or better than that of NPB by contrasting the results of device fabrications with two different emissive materials that are TB-based and non-TB-based. This in conjunction with the ease of synthesis of TB1–2 should render them appealing choices as HTMs.

Broadband-Emitting 2 D Hybrid Organic–Inorganic Perovskite Based on Cyclohexane-bis(methylamonium) Cation

A new broadband-emitting 2 D hybrid organic-inorganic perovskite (CyBMA)PbBr4 based on highly flexible cis-1,3-bis(methylaminohydrobromide)cyclohexane (CyBMABr) core has been designed, synthesized, and investigated, highlighting the effects of stereoisomerism of the templating cation on the formation and properties of the resulting perovskite. The new 2 D material has high exciton binding energy of 340 meV and a broad emission spanning from 380 to 750 nm, incorporating a prominent excitonic band and a less intense broad peak at room temperature. Significant changes in the photoluminescence (PL) spectrum were observed at lower temperatures, showing remarkable enhancement in the intensity of the broadband at the cost of excitonic emission. Temperature-dependent PL mapping indicates the effective role of only a narrow band of excitonic absorption in the generation of the active channel for emission. Based on the evidences obtained from the photophysical investigations, we attributed the evolution of the broad B-band of (CyBMA)PbBr4 to excitonic self-trapped states.

Guest-responsive structural adaptation of a rationally-designed molecular tweezer based on Tröger’s base

AbstractWe have designed and synthesized a modified Tröger’s base TB in which the sterically-rigidified aryl rings that protrude into its groove were envisaged to preclude self-inclusion. From a limited preliminary experimentation, TB has been found to exhibit guest inclusion. The X-ray determined structures of the crystals of guest-free TB and its inclusion compounds with acetonitrile and o-dichlorobenzene reveal remarkable adaptability of the TB core to undergo subtle structural changes in response to the guest that is included. The structural analyses demonstrate the fact that TB behaves like a molecular tweezer. Graphical AbstractX-ray determined crystal structures of the guest-free Tröger’s Base derivative (TB) and its inclusion compounds with acetonitrile and o-dichlorobenzene reveal that TB functions like a molecular tweezer with remarkable adaptability to undergo subtle structural changes in response to the guest that is included.

High Stability Bilayered Perovskites through Crystallization Driven Self-Assembly

In this manuscript we reveal the formation of bilayered hybrid perovskites of a new lower dimensional perovskite family, (CHMA)2(MA)n-1PbnI3 with n = 1-5, with high ambient stability via its crystallization driven self-assembly process. The spun-coated perovskite solution tends to crystallize and undergo phase separation during annealing, resulting in the formation of 2D/3D bilayered hybrid perovskites. Remarkably, this 2D/3D hybrid perovskites possess striking moisture resistance and displays high ambient stability up to 65 days. The bilayered approach in combining 3D and 2D perovskites could lead to a new era of perovskite research for high-efficiency photovoltaics with outstanding stability, with the 3D perovskite providing excellent electronic properties while the 2D perovskite endows it moisture stability.