4-[5-(Naphthalen-1-ylmethyl)-1,3,4-thiadiazol-2-yl]benzene-1,3-diol (NTBD) was extensively studied through stationary UV–vis absorption and fluorescence measurements in various solvents and solvent mixtures and by first-principles quantum chemical calculations. It was observed that while in polar solvents (e.g., methanol) only a single emission band emerged; the analyzed 1,3,4-thiadiazole derivative was capable of producing dual fluorescence signals in low polarity solvents (e.g., n-hexane) and certain solvent mixtures (e.g., methanol/water). As clearly follows from the experimental spectroscopic studies and theoretical modeling, the specific emission characteristic of NTBD is triggered by the effect of enol → keto excited-state intramolecular proton transfer (ESIPT) that in the case of solvent mixture is reinforced by aggregation of thiadiazole molecules. Specifically, the restriction of intramolecular rotation (RIR) due to environmental hindrance suppresses the formation of non-emissive twisted intramolecular charge transfer (TICT) excited keto* states. As a result, this particular thiadiazole derivative is capable of simultaneously producing both ESIPT and aggregation-induced emission (AIE).

A novel coordination motif comprising [4]helicene fused with pyrazino‐phenanthroline ( H4PP ) has been synthesized and reacted with ReCl(CO) ₅ to yield its rhenium(I) complex ( Re‐H4PP ). Absorption and emission spectroscopic analysis conducted in dichloromethane and 2‐methyltetrahydrofuran reveals that combining pyrazino‐phenanthroline with helicene visibly affects the photophysical attributes of both the resulting ligand and its Re(I) complex as compared to their non‐helicene analogues, and even more importantly leads to relatively high photoluminescence quantum yield values, especially in the case of H4PP (29 %). Chiroptical studies through electronic circular dichroism and circularly polarized luminescence performed on enantiomerically enriched samples of Re‐H4PP show the chiral nature of low‐energy excited states affording notable g _lum values that amplify at cryogenic temperatures. Insights into experimental results are provided via first‐principles quantum‐chemical calculations showing important role of intra‐ligand charge‐transfer (ILCT) and metal‐to‐ligand CT (MLCT) states in determining photophysical features of these systems.

We present the first CPL-active helicenic copper( i ) chloride complexes bearing a monodentate N -(carbo[6]helicenyl)–NHC ligand, together with experimental and theoretical analyses of their stereochemical, photophysical and chiroptical features.

Room-temperature luminescence for 7-diethylamino-4-hydroxycoumarin (16C) was investigated in solvents of varying polarity and viscosity, such as methanol, propylene glycol, and in poly(vinyl alcohol) (PVA) matrix. Experimental studies were complemented by extensive quantum-chemical calculations, including spin-orbit coupling, to elucidate the deactivation pathways of the emissive singlet to triplet excited states and to assess the influence of tautomerism on the photophysical properties of the compound. Both fluorescence and phosphorescence were observed for 16C in the PVA film, centered at around 400 and 500 nm, respectively. Interestingly, phosphorescence was highly efficient at room temperature, exhibiting a long lifetime of up to 764 ms and ca. 3 s afterglow under naked eye observation. The pronounced emission anisotropy observed in PVA confirms strong immobilization of embedded 16C molecules. Computational studies indicate that the triplet-state manifold is accessed via intersystem crossing occurring primarily in the diketo form of 16C between the first singlet excited state of mixed 1ππ*/1CT character and a low-energy 3nπ*-type triplet involving C4=O carbonyl group present in this tautomer, highlighting an intriguing tautomeric dependence of the emission in this derivative. The presented system offers a promising platform for the development of new materials exhibiting robust fluorescence and phosphorescence, governed by a proton-transfer process.