No abstract

Optoelectronic properties of organic chromophores (OCPs) are to a large extent dictated by the chemical structures. Herein, we synthesized a new series of ionic phosphorus(P)-heteropines via the methylation of the P(III) center. Our studies revealed that methylation is highly dependent on the P(III) environments (NPN, NPC, and CPC), in which adjacent nitrogen atoms greatly withdraw electron density of the P(III) center. The observation of noncovalent interactions between solvent molecules and the molecular backbones of the related P-heterocycle in the single crystal structure implied tunable molecular conformations. Different from the red-shifted absorption and emission spectra of ionic P-OCPs induced by either decreased lowest unoccupied molecular orbital (LUMO) or intramolecular charge transfer (ICT) state in previous studies, current ionic P-heterocycles exhibit blue-shifted absorption and emission spectra compared to the nonionic counterparts. Our experimental and theoretical studies suggest that the unexpected photophysical characters are probably due to the counter-anion induced structure twisting via intermolecular noncovalent interactions between NH-indole and O(OTf), and/or strong intermolecular O•••F bonding between O(MI) and F(OTf). Our studies also revealed that the P-environments (NPN, NPC, and CPC) conjunctly impact the photophysical properties of the ionic P-heteropines. Overall, the fact that the P-environment-regulated noncovalent interactions induce the rich structure dynamics and photophysics offers us with a new and effective strategy to fine-tune the optical properties of OCPs.

The innovation of approach to synthesize high quality lead perovskite nanocrystals enable prosperous development of nanocrystal based optoelectronic devices in recent years. However, the transfer of this approach to tin...

hand, defects in perovskite such as vacancy, interstitial, and antisite induce the formation of electronic trap states, lead to charge accumulation and non-radiative recombination, and ultimately deteriorate the device efficiency. [13][14][15] It is requisite to develop new strategies to heal these defects to enhance device performances. [16,17] On the other hand, most FA-based perovskite films are prepared under the strictly dry condition (i.e., inside a glovebox). It would largely increase the processing cost to maintain such an atmospheric condition and eventually hinder their commercialization. More efforts are thus needed to optimize the film processing conditions to realize the ambient fabrication of the FA-based perovskite while maintaining the high device efficiency. [18] Water, commonly regarded as inimical for perovskite, unanticipatedly showed beneficial effects in film processing. [18][19][20] It was reported that water trace in the MAPbI 3 precursor induced the formation of hydrate species which influenced film crystallization kinetics and eventually improved film morphologies. [21][22][23] More importantly, it was confirmed that annealing perovskite films in the humid condition could considerably improve film qualities. During the annealing of the MAPbI 3 film, a certain degree of moisture effectively modifies grain boundaries, reduces defects, and alters the morphology and optoelectronic property of the resultant film. [24][25][26] For the FA-based perovskite, the annealing-with-humidity-exposure (humidity-annealing) strategy was practically employed in the fabrication of PSCs with the record PCEs. [7,27] However, there is no direct evidence of the beneficial effect of atmospheric humidity in film processing and the underlying mechanism remains obscure.Herein, we systematically investigate the influence of atmospheric conditions on the sequential deposition of FA-based perovskite films, and attempt to elucidate the underlying mechanism by a set of in situ and ex situ analyses. Three atmospheric conditions are applied in the film annealing process, namely dry (DR, N 2 ), low humidity (LHM, 30-40% relative humidity, RH), and high humidity (HHM, 70-80% RH). Morphological investigations reveal that films prepared in humid conditions possess less pinholes and smoother surfaces. Crystallographic investigations indicate that the different atmospheric conditions show a negligible influence on the crystallinity and orientation of the resultant films. For device application, the film prepared under LHM shows the optimized PCE, mainly derived from the increased open-circuit voltage (V OC ) and fill factor (FF). Further optoelectronic characterizations confirm that the improvements Formamidinium (FA)-based perovskite material holds great potential to deliver highly efficient commercial solar cells. However, the FA-based perovskite films are commonly processed under a strictly controlled environment, which would eventually hinder their way to commercialization. Herein, a systematic study is conducted to investi...

Harvesting high-energy excited-state energy is still challenging in organic chromophores. An introduction of boron atoms along the short axis of the diazapentacene backbone induces multiple emission characteristics. Our studies reveal that the weak molecular orbital (MO) coupling of the S 3 −S 1 transition is responsible for the slow internal conversion rates. Such MO coupling-regulated anti-Kasha emission is different from the large band gap-induced anti-Kasha emission character of classical azulene derivatives. Theoretical studies reveal that a strong MO coupling of the S 3 −S 0 transition is responsible for the higher photoluminescence quantum yield of the anti-Kasha emission in a more polar solution (tetrahydrofuran: 11%; cyclohexane: 0%). Such an MO coupling factor is generally overlooked in anti-Kasha emitters reported previously. Furthermore, the multiple emission can be regulated by solvent polarity, solvent temperature, and fluoride anion binding. As a proof of concept of harvesting high-energy emission, the multiple emission character has allowed us to design single-molecule white-light-emitting materials.