We present a structural and optoelectronic study of 1D piperidinium, pyridinium, and 3-hydroxypyridinium lead trihalides.

Upon irradiation, the electrons in the novel quasi-1D metal organic perovskites are excited from the halide anions onto the aromatic pyridinium cations.

2D halide perovskite‐like semiconductors are attractive materials for various optoelectronic applications, from photovoltaics to lasing. To date, the most studied families of such low‐dimensional halide perovskite‐like compounds are Ruddlesden–Popper, Dion–Jacobson, and other phases that can be derived from 3D halide perovskites by slicing along different crystallographic directions, which leads to the spatially isotropic corner‐sharing connectivity type of metal‐halide octahedra in the 2D layer plane. In this work, a new family of hybrid organic–inorganic 2D lead halides is introduced, by reporting the first example of the hybrid organic–inorganic post‐perovskite 3‐cyanopyridinium lead tribromide (3cp)PbBr3. The post‐perovskite structure has unique octahedra connectivity type in the layer plane: a typical “perovskite‐like” corner‐sharing connectivity pattern in one direction, and the rare edge‐sharing connectivity pattern in the other. Such connectivity leads to significant anisotropy in the material properties within the inorganic layer plane. Moreover, the dense organic cation packing results in the formation of 1D fully organic bands in the electronic structure, offering the prospects of the involvement of the organic subsystem into material's optoelectronic properties. The (3cp)PbBr3 clearly shows the 2D quantum size effect with a bandgap around 3.2 eV and typical broadband self‐trapped excitonic photoluminescence at temperatures below 200 K.

376Results of quantum-chemical studies of the nile red (NR) molecule and its protonated structures by the INDO/S method are presented. It is demonstrated that the best agreement between the calculated and experimental data is obtained for the flat molecule in the ground electron state. Energies of the strongest singlet and triplet electronic states, molecular nature of these states, transition oscillator force, dipole moments in the ground and excited states, electron density distribution around atoms and molecular fragments in the S 0 and S 1 states, and rate constants of radiative, internal, and intercombination conversion are presented for the NR molecule and its protonated structures. The most probable NR protonation centers are analyzed using the molecular electrostatic potential (MESP) method. It is established that the reaction of proton addition to the NR molecule proceeds at the cyclic nitrogen atom. As demonstrated the results of quantum-chemical calculations, low fluorescent properties of the protonated NR structures (with a quantum yield of 4%) are due to a high rate of the S 1 -T 4 intercombination conversion.Keywords: nile red, protonated nile red structure, quantum-chemical investigations, INDO/S method, electron absorption spectra, fluorescence, photophysical parameters.Nile red (NR) is a widely known yellow-red laser dye that possesses clearly pronounced solvatofluorochromic properties [1]. These properties allow NR to be used to determine polarities of biological objects and polymeric and organic-inorganic systems, including proteins and ormosils, to synthesize optical sensor materials to detect the presence of vapors of various organic solvents, etc. [2][3][4].Owing to the presence of proton-acceptor oxygen and nitrogen atoms in the NR molecule ( Fig. 1) in acidic media, the protonated structure possessing the spectral and luminescent properties that differ from the properties of the neutral molecule can be formed.In the present work, the spectral and luminescent properties of NR and its protonated structures are investigated both theoretically and experimentally. EXPERIMENTALThe spectral and luminescent properties of NR and its protonated structures were theoretically investigated using the quantum-chemical software package based on the method of intermediate neglect of differential overlap (INDO) with special spectroscopic parameterization [5]. The software package allowed calculations of the following characteristics of the electronically excited states of polyatomic molecules: the energy and nature of molecular orbitals, energy of singlet and triplet electronically excited states, oscillator force and polarization of electron transitions, electron density distribution around atoms and bonds of the molecule, and dipole moments in the ground and excited

Halide perovskites are promising semiconductor materials for optoelectronics.