Yuyin Wang

Effects of elevated temperature on photosynthesis in desert plant Alhagi sparsifolia S

Most plants growing in temperate desert zone exhibit brief temperature-induced inhibition of photosynthesis at midday in the summer. Heat stress has been suggested to restrain the photosynthesis of desert plants like Alhagi sparsifolia S. It is therefore possible that high midday temperatures damage photosynthetic tissues, leading to the observed inhibition of photosynthesis. In this study, we investigated the mechanisms underlying heat-induced inhibition of photosynthesis in A. sparsifolia, a dominant species found at the transition zone between oasis and sandy desert on the southern fringe of the Taklamakan desert. The chlorophyll (Chl) a fluorescence induction kinetics and CO2 response curves were used to analyze the thermodynamic characters of both photosystem II (PSII) and Rubisco after leaves were exposed to heat stress. When the leaves were heated to temperatures below 43°C, the initial fluorescence of the dark-adapted state (Fo), and the maximum photochemical efficiency of PSII (Fv/Fm), the number of active reaction centers per cross section (RCs) and the leaf vitality index (PI) increased or declined moderately. These responses were reversed, however, upon cooling. Moreover, the energy allocation in PSII remained stable. The gradual appearance of a K point in the fluorescence curve at 48°C indicated that higher temperatures strongly impaired PSII and caused irreversible damage. As the leaf temperature increased, the activity of Rubisco first increased to a maximum at 34°C and then decreased as the temperature rose higher. Under high-temperature stress, cell began to accumulate oxidative species, including ammoniacal nitrogen, hydrogen peroxide (H2O2), and superoxide (O2·−), suggesting that disruption of photosynthesis may result from oxidative damage to photosynthetic proteins and thylakoid membranes. Under heat stress, the biosynthesis of nonenzyme radical scavenging carotenoids (Cars) increased. We suggest that although elevated temperature affects the heat-sensitive components comprising of PSII and Rubisco, under moderately high temperature the decrease in photosynthesis is mostly due to inactivation of dark reactions.

Comparison of parameters estimated from A/Ci and A/Cc curve analysis

The parameters estimated from traditional A/Ci curve analysis are dependent upon some underlying assumptions that substomatal CO2 concentration (Ci) equals the chloroplast CO2 concentration (Cc) and the Ci value at which the A/Ci curve switches between Rubisco- and electron transport-limited portions of the curve (Ci-t) is set to a constant. However, the assumptions reduced the accuracy of parameter estimation significantly without taking the influence of Ci-t value and mesophyll conductance (gm) on parameters into account. Based on the analysis of Larix gmelinii’s A/Ci curves, it showed the Ci-t value varied significantly, ranging from 24 Pa to 72 Pa and averaging 38 Pa. t-test demonstrated there were significant differences in parameters respectively estimated from A/Ci and A/Cc curve analysis (p<0.01). Compared with the maximum ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) carboxylation rate (Vcmax), the maximum electron transport rate (Jmax) and Jmax/Vcmax estimated from A/Cc curve analysis which considers the effects of gm limit and simultaneously fits parameters with the whole A/Cc curve, mean Vcmax estimated from A/Ci curve analysis (Vcmax-Ci) was underestimated by 37.49%; mean Jmax estimated from A/Ci curve analysis (Jmax-Ci) was overestimated by 17.8% and (Jmax-Ci)/(Vcmax-Ci) was overestimated by 24.2%. However, there was a significant linear relationship between Vcmax estimated from A/Ci curve analysis and Vcmax estimated from A/Cc curve analysis, so was it Jmax (p<0.05).

Reduction of the singlet–triplet energy gap of a thermally activated delayed fluorescence emitter by molecular interaction between the host and the emitter

We reported the comparative effect of 1,3-bis(9H-carbazol-9-yl) benzene (mCP) and 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBI) hosts on the PL characteristics of 2-phenyl-4′-carbazole-9H-thioxanthen-9-one-10,10-dioxide (TXO-PhCz). Strong interaction between TXO-PhCz and TPBI can be observed, leading to the lower singlet–triplet energy gap of 8.8 meV and non-monotonic increase of ΦTotle, ΦD, and ΦP with temperature. OLEDs based on TXO-PhCz:TPBI films afford a maximum current efficiency of 71.9 cd A−1, a maximum power efficiency of 45.2 lm W−1, and a maximum EQE of 23.2%.

[(CH3)3NH]3Bi2I9: A Polar Lead-Free Hybrid Perovskite-Like Material as a Potential Semiconducting Absorber

Perovskite hybrids of lead organometal halides, most notably CH3 NH3 PbI3 , have shown extremely promising applications in the field of optoelectronics, because of their remarkable semiconducting and light-absorbing properties. However, two key issues-the toxicity of lead and the poor ambient instabilities-have restrained their further commercialization. Herein, we have designed a new stable polar lead-free hybrid material by utilizing the strategy of cation substitution, [(CH3 )3 N]3 Bi2 I9 (1), which adopts the 0D inorganic perovskite-like architecture by face-sharing BiI6 octahedra. It is interesting that 1 displays excellent absorbing properties with a narrow optical band gap of ≈2.0u2005eV, and positive temperature-dependent conductivity confirms its semiconducting behaviors. In addition, 1 has good phase stability against decomposition under ambient conditions, much superior to that of CH3 NH3 PbI3 . This work suggests the potential of 1 as a lead-free semiconducting absorber with high phase stability for photoelectric applications.

Lead-Free Hybrid Material with an Exceptional Dielectric Phase Transition Induced by a Chair-to-Boat Conformation Change of the Organic Cation

Hybrid organic-inorganic perovskite materials have demonstrated great potential in the field of photovoltaics and photoelectronics. On the basis of the high degree of structural flexibility and compatibility, diverse molecular functional materials have been assembled by modifying the length of the organic components and/or dimensionality of the inorganic frameworks. In this paper, we present a chiral lead-free organic-inorganic hybrid, (piperidinium)2SbCl5 (1), which follows the one-dimensional inorganic frameworks of the corner-sharing SbCl6 octahedra. Strikingly, 1 displays a dielectric phase transition at Tc = 338 K, changing from the chiral space group of P212121 to polar Pna21 upon heating. Crystal structure analyses reveal that an unusual thermally activated conformation change of the piperidinium cations affords the driving force to the phase transition of 1. That is, organic piperidinium moieties display a chairlike conformation below Tc, which transforms to a boatlike structure above Tc. Such an unprecedented change is strongly coupled to the dielectric transition along with notable steplike anomalies, which suggest that 1 could be used as a potential switchable dielectric material. Besides, the temperature-dependent conductivity and theoretical analysis of its electronic structure disclose the semiconducting behavior of 1. This study paves the pathway to the design of new lead-free semiconducting perovskites with targeted properties for optoelectronic application.

(2-Methylpiperidine)PbI3: an ABX3-type organic–inorganic hybrid chain compound and its semiconducting nanowires with photoconductive properties

Organic–inorganic hybrid semiconducting nanowires have recently been widely regarded as promising candidates for electric and optical applications due to their faster carrier separation and low charge recombination. Here, we reported organic–inorganic hybrid semiconducting nanowires with photoconductive properties based on a one dimensional ABX3-type compound, (2-methylpiperidine)PbI3 (1). In 1, one dimensional infinite double chains are surrounded by protonated organic 2-methylpiperidine cations to form a quantum wire structure, which has been thought to be favorable for carrier transport. Furthermore, the prepared semiconducting nanowires of 1 display obvious photoconductive properties, which have been verified using I–V and time-dependent photoresponse measurements. All the results indicate that such semiconducting nanowires based on low dimensional organic–inorganic hybrid materials have potential photoelectric applications.

Switchable behaviors of quadratic nonlinear optical properties originating from bi-step phase transitions in a molecule-based crystal

Solid-state nonlinear optical (NLO) switches are recently emerging as a new class of promising stimuli-responsive materials for photoelectric application. Herein, we report an organic molecular crystal, N- methylcyclohexylamine picrate (1), which exhibits remarkable switching behaviors of quadratic NLO properties with a large contrast of ∼20 between its NLO-on and NLO-off states. This is almost comparable with the conventional photochromic counterparts, and suggests the great potential of 1 as a quadratic NLO-switching candidate. It is noteworthy that 1 undergoes bi-step structural phase transitions at T1 = 240 K and T2 = 285 K, which are closely associated with its NLO-switching activities. Above T1, disordering of anionic and cationic moieties leads to vanishing of the NLO effect, (i.e. NLO-off state). In contrast, below T1, stepwise frozen ordering of the structural moieties generates strong NLO activities, with the NLO response being ∼0.9 times that of KH2PO4. Such an order–disorder transformation accounts for the high-contrast NLO switching of 1. It is believed that this finding affords an effective strategy for designing new stimuli-responsive materials.

[C6H14N]PbBr3: An ABX3‐Type Semiconducting Perovskite Hybrid with Above‐Room‐Temperature Phase Transition

Organic-inorganic hybrid perovskites, with the formula ABX3 (A=organic cation, B=metal cation, and X=halide; for example, CH3 NH3 PbI3 ), have diverse and intriguing physical properties, such as semiconduction, phase transitions, and optical properties. Herein, a new ABX3 -type semiconducting perovskite-like hybrid, (hexamethyleneimine)PbBr3 (1), consisting of one-dimensional inorganic frameworks and cyclic organic cations, is reported. Notably, the inorganic moiety of 1 adopts a perovskite-like architecture and forms infinite columns composed of face-sharing PbBr6 octahedra. Strikingly, the organic cation exhibits a highly flexible molecular configuration, which triggers an above-room-temperature phase transition, at Tc =338.8u2005K; this is confirmed by differential scanning calorimetry (DSC), specific heat capacity (Cp ), and dielectric measurements. Further structural analysis reveals that the phase transition originates from the molecular configurational distortion of the organic cations coupled with small-angle reorientation of the PbBr6 octahedra inside the inorganic components. Moreover, temperature-dependent conductivity and UV/Vis absorption measurements reveal that 1 also displays semiconducting behavior below Tc . It is believed that this work will pave a potential way to design multifeatured perovskite hybrids by utilizing cyclic organic amines.

A lead-free semiconducting hybrid with ultra-high color rendering index white-light emission

Organic–inorganic hybrid perovskites (OIHPs) of lead halides have played a significant role in the field of light-emitting devices and display systems. However, the potential toxicity of lead is considered as one of the main problems for further applications, and it is highly desirable to design the new lead-free OIHPs with outstanding white light emission. Herein, we present a new lead-free single-component hybrid as the potential white light-emitting semiconducting material, [4-methylpiperidinium]2SbCl5 (4-MPSC), which adopts the one-dimensional inorganic chains of corner-sharing SbCl6 octahedra. It is worth noting that 4-MPSC shows the Commission internationale de l’eclairage (CIE) chromaticity coordinates of (0.33, 0.32), which is highly close to the pure white light emission value of (0.33, 0.33). Meanwhile, the white-light emission of 4-MPSC shows an ultra-high color rendering index (CRI) value of 96.29. It is believed that such an ultra-high CRI value will fulfil the requirement for color-critical high-level potential applications. Moreover, 4-MPSC also exhibits semiconducting properties, as verified by the positive temperature-dependent conductivity along with an optical bandgap of 2.93 eV. This work will provide a pathway for further design of new white-light-emitting materials in the lead-free OIHP system.

Dielectric phase transition triggered by the order–disorder transformation of cyclopropylamine in a layered organic–inorganic halide perovskite

Cyclic organic amines are emerging as excellent building blocks to assemble organic–inorganic hybrid phase transition materials due to their flexible cyclic structure. Herein, we used a three-membered ring organic amine, cyclopropylamine, assembling a layered organic–inorganic hybrid dielectric phase transition compound ([C3H5NH3]2[CdCl4], CPA) that displays a remarkable switchable dielectric response induced by an order–disorder transformation of the organic moiety. More specifically, the dielectric constant of CPA can be tuned between high- and low-dielectric states at ∼273 K, which demonstrates its potential application in a switchable dielectric field. In addition, theoretical analysis of electronic band structures suggests that CPA exhibits a direct-band-gap with the value of 5.20 eV. This solid-state structural phase transition triggered by ordering of a three-membered ring organic amine is reported for the first time, and it highlights a new potential strategy to design switchable dielectric materials.