Annamalai University

The spectral characteristics of 2-phenylenediamine (2PDA) in various solvents, and in the presence of α-cyclodextrin (α-CD) and β-cyclodextrin (β-CD) at pH~3, and pH ~7, were investigated using UV–visible, fluorescence, time-resolved fluorescence measurements, and PM3 computational methods. 2PDA showed a single broad emission band in all solvents, whereas dual emission observed in CD solutions indicates the presence of excimer in the 2PDA molecule. The fluorescence lifetimes of the inclusion complexes were greater than that of free 2PDA. In the 2PDA molecule, both the vertical and horizontal bond lengths between the both amino groups are smaller than the β-CD cavity size The Ag:2PDA:α-CD and Ag:2PDA:β-CD nanomaterials were synthesized and characterized by SEM, FTIR, and DSC techniques. In all pH conditions, 2PDA exhibited distinct absorption and emission shifts upon complexation with α-CD and β-CD. SEM–EDX data confirmed the presence of 5.5% silver in the nanomaterials.

This paper presents an extensive experimental and theoretical investigation of the cesium-doped methylammonium lead triiodide (Cs: MAPbI₃), a hybrid inorganic-organic perovskite that exhibits high photovoltaic and nonlinear optical (NLO) promise. The reaction mechanism at the molecular level suggests coordination of the Pb²⁺ with the iodide ions and Cs⁺-induced zwitterionic nature, which favors exciton dissociation and charge separation. Crystallographic analysis reveals favored crystallization in the (101) plane and reveals a three-dimensional intricate system of molecular slabs, tubular morphologies, helical molecular strips, and sloping planes, all for anisotropic charge transfer. The pseudo-tetragonal lattice exhibits low Microstrain (ε = 3.49 × 10⁻⁴), high crystallite dimension (812.2 nm), and high phase purity, as established by XRD and SEM studies. Electrochemical impedance spectroscopy gives low series resistance (Rs = 15.2 Ω) and high recombination resistance (Rrec = 600 Ω), suggestive of optimal carrier transport. Band gap value optimized to ~ 1.55–1.63 eV is comparable with the Shockley–Queisser limit, and the material has a high external quantum efficiency (EQE ~ 86%). Spectroscopic analyses (FT-IR, FT-Raman, NMR) authenticate polar strong interactions (e.g., Pb-I, Pb-H, Cs-I), which are responsible for vibrational coupling and dielectric modulation. Theoretical calculations, such as APT, Mulliken population, HOMO-LUMO analysis, UV-Vis absorption, and NBO analysis, indicate extensive delocalization of electrons, strong orbital hybridization, and favourable dipole alignment, along with highly developed hyperpolarizability (βtot = 528.19 × 10⁻³³ esu) to facilitate intense second-order NLO activity. MEP map and exciton cavity analysis emphasize dipolar energy landscapes conducive to exciton confinement and dissociation. Collectively, these photophysics, electronics, and structure result in Cs: MAPbI₃ as a structurally stable, optically active, and electronically tuneable material that is best suited for high-performance applications in solar energy and nonlinear photonics.