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

Abstract

The crystals of novel benzo [b]naphtho [1,2-d]furan-6-one-type fluorophores (1) exhibit sensitive colour and fluorescence change upon enclathration of organic solvent molecules. The crystal of the fluorophore 1b (R = Bu) exhibits fluorescence decrease upon inclusion of cyclohexane, however, the crystal of the fluorophore 1c (R = Ph) exhibits a drastic fluorescence enhancement upon inclusion of chloroform. To elucidate the enclathrated guest effects on the photophysical properties of the crystals, the X-ray crystal structures of the guest-free and guest-inclusion compounds have been determined. On the basis of the spectral data and the crystal structures, the effects of the enclathrated guest on the solid-state photophysical properties of the clathrate compounds are discussed.( IntroductionThe development of fluorescent molecular sensors is of importance because of the detection of cations, anions and biochemical analyses such as amino acids and applicable to a fluorescent switch.[1] A number of fluorophores have been developed, and the relation between the chemical structure and their fluorescence properties in solution have been investigated in order to elucidate the mechanism of fluorescence changes upon formation of complexes with cations, anions, and neutral molecules.[2] However, only several fluorescent hosts that exhibit fluorescence change upon enclathration of organic solvent molecules in the crystalline state have been reported. [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. In the previous paper, we have reported the absorption and fluorescence properties in solution and in the solid state of novel heterocyclic quinol-type fluorophores, 5-hydroxy-5-substituent-(1) and 3-hydroxy-3-substituent-benzo[kl]xanthen-2-one (2) fluorophores (Scheme 1). [7] Here, we report sensitive colour and fluorescence change of the quinol 1 upon enclathration of organic solvent molecules in the solid state. The X-ray crystal structures of 1 and its guest-inclusion compounds have been determined, on the basis of which the enclathrated guest effects on the solid-state fluorescence properties are discussed. Results and Discussion Inclusion Ability in the Crystalline StateIn order to investigate their inclusion ability, we recrystallized the quinol compounds from various organic solvents such as ethanol, acetonitrile, cyclohexane, chloroform, benzene, 1,4-dioxane and morpholine. The quinols 1a and 2a-2c did not form any inclusion compounds. However, we have found tha...

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

“…Strong intermolecular π-π interactions between the fluorophores induce a large redshift in the absorption and fluorescence maxima and an intense fluorescence quenching in the solid state. [2,3,5,9] However, the solidstate fluorescence intensity of 2·ethanol is weaker than that of 2·ethyl acetate. It is considered that the continuous intermolecular hydrogen bonding ranging alternately host and www.eurjoc.orgguest (···H···G···H···) was only observed in 2·ethanol, which is a principal factor leading to fluorescence quenching in the solid state.…”

“…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.…”

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

“…These long-range host-host interactions based on continuous intermolecular hydrogen bonds and π-π interactions would cause a strong fluorescence quenching in the guest-free crystal. [5][6][7][8]11] In contrast, in the case of the carboxylic acid inclusion crystals, such direct intermolecular hydrogen bonding between host molecules is not found. Instead, the carboxylic acid inclusion crystals, except those of 1·[HOOC(CH 2 ) 8 -COOH] 2 , are made up of a hydrogen-bonded cluster unit composed of two imidazole hosts and four carboxylic acid guests ( Figures 7, 8 and 9).…”

“…[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.…”

Impact of molecular structure on intermolecular interactions and organic solid state luminescence in supramolecular systems

“…Solid state organic luminescent materials particularly with tunable luminescence are of great interest in recent years, because of their applications in the field of optoelectronic devices, including organic electroluminescence (EL), light‐emitting diodes (LEDs), and optical sensors 1–8. Organic molecules, for example, π‐conjugated molecules show high luminescence in dilute solution9–15 but become weakly luminescent in the solid state due to the formation of less emissive species such as excimers that restrict the applications of these molecules in high density optical systems 16, 17. Strategies, such as the introduction of bulky substituents or the synthesis of propeller‐shaped luminescent molecules which prevent close‐packing in the solid state, have successfully lead to organic molecules that luminescence in the solid state 18–22.…”