Fluorescence Sensing Behavior of Crystals of an Imidazole-Type Clathrate Host upon Contact with Gaseous Carboxylic Acids

Abstract

The crystals of the title fluorescent clathrand exhibit a drastic fluorescence enhancement behavior upon contact with carboxylic acid vapors. The magnitude of the fluorescence change is greatly dependent on the enclathrated carboxylic acid molecules and increase in the following order: formic acid < acetic acid < propionic acid. To elucidate the enclathrated guest effects on the fluorescence properties of the crystals, the X-ray crystal structures have been determined.

Heterocyclic Quinol‐Type Fluorophores: Solid‐State Fluorescence Change in Crystals of Benzo[b]naphtho[1,2‐d]furan‐6‐one‐Type Fluorophore upon Inclusion of Organic Solvent Molecules

“…A large red-shift of the absorption and fluorescence maxima and the solid-state fluorescence quenching by strong donor-acceptor type π-π interactions of fluorescent dyes are known. [4][5][6][7][8][9][10] In fact, the fluorescence emission intensities of 1a-1c are in the order of 1c>1b>1a in the crystalline state. In the crystal of 1b, a donor-acceptor type of π-stacking between a pair of quinol enantiomers is observed, however, the rang of the π-stacking is less than that of 1a.…”

“…[3] We have recently developed novel benzofurano [3,2-b]naphthoquinol-type [4] , imidazo [5,4-a]anthraquinol-type [5] and phenanthro [9,10-d]imidazole-type [6] fluorescent hosts whose crystals exhibit a dramatic fluorescence enhancement upon inclusion of various gaseous amines, organic solvents and carboxylic acids, respectively. From the relation between the solidstate fluorescence properties and the crystal structures, it was confirmed that the destruction of π-π interactions between the fluorophores by guest enclathratation is the main reason for the guest-dependent fluorescence enhancement behaviour.…”

Drastic Solid‐State Fluorescence Enhancement Behaviour of Phenanthro[9,10‐d]imidazole‐Type Fluorescent Hosts upon Inclusion of Carboxylic Acids

“…[1][2][3][4] Several types of fluorescent hosts exhibit fluorescence enhancement behaviour with a blueshift in the fluorescence wavelength maximum upon inclusion of various organic solvent molecules. [5][6][7][8][9][10][11] From comparison of the X-ray crystal structures of the guest-free and several clathrate compounds, it was concluded that the changes in molecular arrangement by the formation of CH-π interactions and the destructions of π-π interactions and the intermolecular hydrogen bonds binding fluorophores by the enclathrated guest molecules are the main reason for the guest-dependent fluorescence enhancement and the blueshift in the fluorescence maximum of the crystals. In contrast, we reported that a new phenanthro [9,10-d]imidazole-type fluorescent host, [12] 2-[4-(diethylamino)phenyl]-1H-phenanthro [9,10-d]imidazole (1; Scheme 1), whose crys-cent intensity changes.…”

Solid‐State Fluorescence Changes of 2‐(4‐Cyanophenyl)‐5‐[4‐(diethylamino)phenyl]‐3H‐imidazo[4,5‐a]naphthalene upon Inclusion of Organic Solvent Molecules

“…In our previous works, we reported novel benzofurano [3,2-b]naphthoquinol-type, [5] imidazo [5,4-a]anthraquinol-type, [8] 5-hydroxy-5-substituent-benzo [b]naphtho[1,2-d]-furan-6-one-type [9] and phenanthro [9,10-d]imidazoletype [10] fluorescent hosts, whose crystals exhibit a dramatic fluorescence enhancement upon inclusion of various amines, organic solvents and carboxylic acids. In particular, imidazo [5,4-a]anthraquinol-type fluorophores, in which two tautomeric forms (A and B) are possible for the imidazole ring, can include various kinds of organic solvent molecules in the crystalline state by changing the tautomeric form of the imidazole ring.…”