Influence of intermolecular interactions on solid state luminescence of imidazopyridines: theoretical interpretations using FMO-TDDFT and ONIOM approaches.

6-Cyano-2-(2'-hydroxyphenyl)imidazo[1,2-a]-pyridine (6CN-HPIP) shows polymorph-dependent luminescence with the three different crystal forms exhibiting the packing-controlled tuning of bright colors, orange, yellow, and red. The distinctive emission in aggregated states was treated with finite cluster models and analyzed by means of quantum chemistry calculations. The influence of structural displacements and intermolecular interactions in the crystalline state on solid state luminescence was examined in detail using the Fragment Molecular Orbital (FMO) scheme, suitable for studies of aggregated molecular systems.

Excited-state intramolecular proton transfer (ESIPT) emission of hydroxyphenylimidazopyridine: computational study on enhanced and polymorph-dependent luminescence in the solid state.

Although 2-(2'-hydroxyphenyl)imidazo[1,2-a]pyridine (HPIP) is only weakly fluorescent in solution, two of its crystal polymorphs in which molecules are packed as stacked pairs and in nearly coplanar conformation exhibit bright excited-state intramolecular proton transfer (ESIPT) luminescence of different colors (blue-green and yellow). In order to clarify the enhanced and polymorph-dependent luminescence of HPIP in the solid state, the potential energy surfaces (PESs) of HPIP in the ground (S(0)) and excited (S(1)) states were analyzed computationally by means of ab initio quantum chemical calculations. The calculations reproduced the experimental photophysical properties of HPIP in solution, indicating that the coplanar keto form in the first excited (S(1)) state smoothly approaches the S(0)/S(1) conical intersection (CI) coupled with the twisting motion of the central C-C bond.

Electronic spectra of cycl[3.3.2]azine and related compounds: solvent effect on vibronic couplings.

Quantitative ab initio calculations are presented for the ultraviolet-visible peaks of cycl[3.2.2]azine and its mono- and dibenzannulated polycyclic compounds at the multistate CASPT2 (MS-CASPT2) level of theory, with 11 nm deviation from the experimental S0 → S1 absorption.

Synthesis, solid-state fluorescence properties, and computational analysis of novel 2-aminobenzo[4,5]thieno[3,2-d]pyrimidine 5,5-dioxides.

New fluorescent compounds, benzo[4,5]thieno[3,2-d]pyrimidine 5,5-dioxides (3a-g), 2-amino-4-methylsulfanylbenzo[4,5]thieno[3,2-d]pyrimidine (6), and 2-amino-4-methylsulfanyl-7-methoxybenzo[4,5]furo[3,2-d]pyrimidine (7), were synthesized in good yields from heterocyclic ketene dithioacetals (1a-c) and guanidine carbonate (2a) or (S)-methylisothiourea sulfate (2b) in pyridine under reflux. Among the fused pyrimidine derivatives, compound 3c, which has an amino group at the 2-position and a benzylamino group at the 4-position of the pyrimidine ring, showed the strongest solid-state fluorescence. The absorption and emission properties of the compounds were quantitatively reproduced by a series of ab initio quantum-chemical calculations.

Faradaic phase transition of dibenzyl viologen on an HOPG electrode surface studied by in situ electrochemical STM and electroreflectance spectroscopy.

Phase transitions of an adsorption layer of dibenzyl viologen (dBV) as a typical diaryl viologen on a basal plane of a highly oriented pyrolytic graphite (HOPG) electrode are described using voltammetry, in situ electrochemical scanning tunneling microscopy (EC-STM), and electroreflectance (ER) spectroscopy. A monolayer redox process at less negative potential than the bulk redox process was found to be the first-order faradaic phase transition between a gaslike adsorption layer of dication (dBV(2+)) and a 2D condensed monolayer of radical cation (dBV(•+)). Comparison of the results of cyclic voltammetry and potential step chronoamperometry was made with those of heptyl viologen (HV), which also undergoes a faradaic phase transition of the first order.