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Two covalent organic framework (COF) films supported by a glass substrate were obtained by solvothermal reaction of an electron donor with electron acceptor 1,3,5-triformylbenzene (TF) or 2,4,6-triformylphloroglucinol (TFP), respectively. The TFP-BD film exhibits a nonlinear absorption coefficient of −3.01 × 105 cm GW−1. The TFP-BD film can aggregate electrons around the connected monomer through the D–A effect due to its highly polar and electronegative carbonyl oxygen atoms, thereby modulating the electronic structure of the COFs. This work provides a novel approach for the structural modulation of optical materials with strong nonlinearity. [ABSTRACT FROM AUTHOR]

Covalent–organic frameworks (COFs) exhibit high structural designability and functional tunability, and have become a promising platform for designing excellent third-order nonlinear optical (NLO) candidate materials. However, their third-order NLO performance is limited by insufficient intramolecular charge transfer. Herein, we synthesized two phenothiazine-based donor–acceptor (D–A) COF films on transparent glass panes via a Schiff base condensation reaction using a solvothermal method. The TFP-TZ using triformylphloroglucinol as an acceptor linker and a phenothiazine-based donor unit exhibits a fully β-ketoenamine conformation due to the irreversible keto–enol tautomerization. At a pulse energy of 15 μJ, TFP-TZ films exhibited nonlinear saturated absorption, with a nonlinear absorption coefficient (β) of −6.78 × 10−7 m W−1, a nonlinear refraction coefficient (n2) of −1.67 × 10−13 m2 W−1, and a third-order nonlinear polarization coefficient (χ(3)) of 4.73 × 10−7 esu. These values are 6.65, 1.82, and 1.91 times higher than those of TF-TZ films imine-linked without the carbonyl group, respectively. The combination of D–A charge transfer properties and irreversible interconversion of salicylideneaniline molecular units results in narrowing of the band gap of COFs, thereby enhancing their third-order NLO performance. [ABSTRACT FROM AUTHOR]

In order to study the fracture ability classification of rock mass under the cracking action of supercritical CO2 phase transition, based on the classification theory of rock mass in blasting engineering, an analytic hierarchy process (AHP)-entropy weight method (EWM) and the cloud model classification method for rock mass cracking under CO2 phase transformation are proposed. In this method, rock density, rock tensile strength, rock wave impedance, and rock mass integrity coefficient are used as the factors to determine the level of rock mass fracturing, and the evaluation index system of rock mass fracturing is established. Through this evaluation method, the rock mass in a reconstruction project section of Nyingchi, Tibet, is classified and evaluated. The results present that this new classification method of rock mass fracture ability uses AHP–EWM to carry out the weight distribution of the classification index. In addition, it is combined with the cloud model for the classification division, overcoming the traditional classification method fixed with appraisal pattern flaw. Therefore, it has validity and feasibility. According to the characteristics of fracture ability, the rock masses in the area to be rebuilt on the Tibet Highway are divided into grade II, grade III, and grade IV, which provides scientific guidance for the construction of the project. [ABSTRACT FROM AUTHOR]