•Synthesis and properties of novel xanthenes dyes having thienyl and thieno[3,2-b]thienyl rings as auxochrome.•More bathochromic than know Rhodamine dye.•Colors only in non-hydrogen-bond acceptor solvents.•A lactone precursor colors by adding strong acids whose pKa value is lower than −2.2, whereas that of rhodamine B lower than 4.7.Novel xanthene dyes having thienyl and thieno[3,2-b]thienyl rings as auxochrome have been synthesized. The UV–vis absorption maximum in dichloromethane was in the order of the auxochrome: NEt2 (Rhodamine B, 558 nm) < 2-thienyl (569 nm) < 5-thieno[3,2-b]thienyl (608 nm). These new xanthene dyes colored only in non-hydrogen-bond accepting solvents such as chloroform and dichloromethane. The lactone precursors of the thienyl and thieno[3,2-b]thienyl derivatives colored by adding strong acids whose pKa value is lower than −2.2 and 0.23, respectively, whereas that of rhodamine B colored by adding weak acids whose pKa value is lower than 4.7. These results originate from less stability of colored cationic dyes by the heteroaromatics than by the diethylamino auxochrome.Download high-res image (253KB)Download full-size image

•4,4,5,5,6,6,6-Heprafluoro-3,3-bis(trifluoromethyl)hexanoic acid exhibited the highest η value (6.20%) among ten co-adsorbents.•Prevention of aggregate formation could improve photocurrentdensity.The effects of co-adsorbents on the performance of D205 in dye-sensitized solar cells were examined. 4,4,5,5,6,6,6-Heprafluoro-3,3-bis(trifluoromethyl)hexanoic acid exhibited the highest conversion efficiency of 6.2% on TiO2 among ten co-adsorbents. This result comes from improved short-circuit photocurrent owing to prevention of aggregate formation.Download high-res image (201KB)Download full-size image

•A novel indoline dye with a carboxylated 1,3-indadione linked with a hexylthienyl ring.•Suitable energy levels and fluorescence lifetime.•The hexyl group is important to exhibit high efficiency.The performance of a new indoline dye having a carboxylated 1,3-idandione unit linked with a hexythienyl ring showed higher conversion efficiency than the analogous dye without the hexyl group.Download high-res image (155KB)Download full-size image

•Any liquid azo dyes were produced.•Introduction of medium n-alkyl group at the ortho-position.•Prevention of π/π stacking, alkyl–alkyl interactions, and intermolecular hydrogen bond.Any liquid azo dyes, in which auxochrome such as dialkylamino, alkoxy, and amino group is attached in a molecule, were produced. In a series of 2-alkyl-4’-(dimethylamino)azobenzenes, the butyl, hexyl, octyl, and dodecyl derivatives were liquid at room temperature, whereas the propyl, 1-methylethyl, 1-methylpropyl, 1,1-dimethylethyl, and octadecyl derivatives were solid. Thus, it is essential for liquid azo dyes to have a medium n-alkyl group at the 2-position. In a series of 2-butyl-4’-(dialkylamino)azobenzenes, the dimethylamino, diethylamino, dibutylamino, dioctylamino, and didodecylamino derivatives were liquid. 2-Butyl-4’-methoxyazobenzene and 4-amino-3,5-dimethyl-2’-butylazobenenzne were also liquid, whereas 2-butyl-4’-hydroxyazobenznene, 4-amino-2’-butylazobenzene, and 2-butyl-4’-(methylamino)azobenzene were solid. The prevention of π/π stacking, alkyl–alkyl interactions, and intermolecular hydrogen bond could produce liquid azo dyes.Liquid azo dyes were produced by introducing a medium n-alkyl group at the o-position for the azo group and restraining hydrogen bonding.

Novel triarylmethane dyes decorated with 2-thienyl, 2-thieno[3,2-b]thienyl, and 2-dithieno[3,2-b:2′,3′-d]thienyl rings as auxochromes were much more bathochromic than the known crystal violet. The hydrol precursors of these new dyes exhibited potential applications as strong and super acid pH sensors.

Novel bisboron complexes of bidentate ligands consisting of 1,4-benzoquinone and two pyrrole rings were synthesized by using a simple two-step reaction. In solution, the bisboron complexes showed absorption maxima at ∼620 and 800 nm, which were attributed to the allowed S0 → S2 and forbidden S0 → S1 transitions, respectively. The bisboron complexes did not show any fluorescence, probably because of their highly symmetrical structure which forbids the S0 → S1 transition. Bisboron complexes underwent a two-electron reduction to yield the corresponding aromatic dianion, which showed absorption maxima at ∼410 nm.

The synthesis and the solution/solid-state fluorescence properties of pyrimidine-based monoboron complexes differing in terms of the substituents [either two fluorine atoms (BF2 complex) or two phenyl groups (BPh2 complex)] on the boron atom are reported herein. Unrestricted C–Ar intramolecular rotation in the non-, trifluoromethyl-, and cyano-substituted derivatives resulted in negligible fluorescence in solution. On the other hand, methoxy- and dimethylamino-substituted analogues caused the restriction of the C–Ar intramolecular rotation and consequently resulted in relatively strong fluorescence in solution. The non-, trifluoromethyl-, and cyano-substituted derivatives showed a pronounced aggregation-induced emission enhancement effect. Dimethylamino-substituted derivatives exhibited solvatochromism in the fluorescence spectra. Substitution with BPh2 effectively enhanced the fluorescence quantum yield compared to the corresponding BF2 complexes in the solid-state.

•Silicate particle covalently bonded with phenolphthalein has been prepared.•It turned pale pink at pH 10.9.•It showed good coloration–discoloration repetition stability.A silicate particle covalently bonded with phenolphthalein was prepared by a sol–gel method. This particle contained ca. 10% of organic component, turned pale pink at pH 10.9, and showed good coloration-discoloration repetition stability.Silicate particle covalently bonded with phenolphthalein turned pale pink at pH 10.9 and showed good coloration-discoloration repetition stability.

To make a molecular design of efficient indoline dyes, fluorescence lifetimes should be longer than ca. 0.8 ns in chloroform, in addition to suitable HOMO and LUMO levels and bathochromic UV-vis absorption bands.

The fluorescence intensity of indolenium carbocyanine dyes in the solid state depended on both the alkyl group on the nitrogen atoms in the indolenium rings and the kind of counter anions. The N-propyl derivative having a bis(trifluoromethylsulfonyl)imide anion, whose fluorescence maximum was observed at 657 nm with shoulder peaks, exhibited the highest fluorescence quantum yield of 0.31. The wave deconvolution of fluorescence spectrum indicated three components assigned to the S1,0→S0,0, S1,0→S0,1, and S1,0→S0,2 transitions. The X-ray structure of this compound indicates an isolated monomer-type packing, whereas the other derivatives shows the isolated dimer-type packing or consequent π/π stacking. The cyanine dye having the least π/π interactions among adjacent cationic fluorophores could exhibit the most intense fluorescence in the solid state.

•Novel single rhodanine indoline dyes have been prepared.•GU112 having both cyanoacrylic and rhodanine acetic acid groups in an anchor moiety exhibited the best stability among GU110, GU111, and GU112 under continuous fluorescent lamp illumination at ambient temperature.A new single rhodanine indoline dye GU112 having both cyanoacrylic and rhodanine acetic acid groups in an anchor moiety showed the best stability among GU110, GU111, and GU112 in zinc oxide dye-sensitized solar cell.

The alkyl groups in 2-(dialkylamino)- and 2,7-bis(dialkylamino)perfluorophenazines drastically affected the melting point and solid-state fluorescence. 2-(Dialkylamino)- and 2,7-bis(dialkylamino) derivatives such as 2-(dioctylamino)-, 2-(didodecylamino)-, and 2,7-bis(dioctylamino)perfluorophenazines were liquid at ambient temperature, whereas shorter and longer dialkylamino derivatives were solid. 2-(Dioctadecylamino)perfluorophenazine exhibited a fluorescence maximum at 581 nm, being significantly blue-shifted compared with the other derivatives, with the most intense fluorescence quantum yield of 0.29 in the crystalline form. This result is attributed to the isolated dimer-type packing coming from long octadecyl groups. 2-(Dimethylamino)perfluorophenazine showed positive fluorescence solvatochromism due to a large dipole moment in the excited state. The computational analysis of (2-(dimethylamino)perfluorophenazine suggests that the red-shift of the fluorescence maximum in the crystalline form, compared with that in solution, mainly comes from π–π interactions with adjacent molecules. The fluorescence lifetime of 2-(dioctadecylamino)perfluorophenazine was significantly longer compared with 2-(dioctadecylamino)phenazine owing to the aromatic C–F bonds.

Pyrazine-based monoboron complexes bearing two fluorine atoms (BF2 complex) or two phenyl groups (BPh2 complex) on the boron atom were synthesized, and the fluorescence properties were investigated. The BPh2 complexes exhibited red-shifted maximum absorption and maximum fluorescence wavelengths and lower molar absorption coefficients than the corresponding BF2 complexes in n-hexane. The fluorescence quantum yields of the BPh2 complexes were higher than or comparable to the corresponding BF2 complexes owing to the relatively low nonradiative rate constants. Although the nonsubstituted and trifluoromethyl-substituted derivatives did not show solvatochromism, the dimethylamino-substituted BF2 and BPh2 complexes exhibited pronounced solvatochromism in the fluorescence spectra. Dual fluorescence was observed for the dimethylamino-substituted BF2 complex in toluene, 1,4-dioxane, and chloroform, corresponding to locally excited (LE) and twisted intramolecular charge-transfer (TICT) states.

•Better performance of DN350 than D149 in the presence of cholic acid on zinc oxide.•The best performance of DN350 in the presence of ursodeoxycholic acid.•Bathochromic shift of UV–vis absorption band of DN350 in the presence of ursodeoxycholic acid.DN350 exhibited better performance than D149 in zinc oxide dye-sensitized solar cell in the presence of cholic acid (CA). The performance of DN350 was improved in the order of cholic acids: ursodeoxycholic acid (UDCA) > chenodeoxycholic acid (CDCA) > CA. This result could come from the bathochromic shift of the UV–vis absorption band of DN350 on zinc oxide to improve short-circuit photocurrent density.Ursodeoxycholic acid (UDCA) was the best co-adsorbent for DN350 in zinc oxide dyesensitized solar cell due to the bathochromic shift of the UV–vis absorption band.

•A series of new pyridinium styryl dyes have been synthesized.•The most intense solid-state fluorescence was observed at 652 nm (Φf = 0.16).•The solid-state fluorescence behavior is attributed isolated dimer-type packing.1-Alkyl-2-[4-(diethylamino)styryl]pyridinium salts showed fluorescence maxima at around 650 nm in the solid state depending on the alkyl group and counter anion. 1-Butyl-2-[4-(diethylamino)styryl]pyridinium bis(perfluorobutylsulfonyl)imide exhibited the fluorescence maximum at 652 nm with the highest quantum yield 0.16 in the crystalline form. The single X-ray crystallography suggests that this compound exhibits isolated dimer-type packing leading to fluorescence in the solid state.

A new indoline dye in which a double rhodanine acceptor is attached to the indoline moiety by a p-phenylene spacer on the indoline–nitrogen, has been examined for its performance as a sensitizer for zinc oxide dye-sensitized solar cells. In the presence of cholic acid, chenodeoxycholic acid, or lithocholic acid; the performance was greatest for lithocholic acid as this showed the greatest reduction in dye H-aggregate formation.Graphical abstractThe best performance was obtained when the dye was adsorbed on zinc oxide in the presence of lithocholic acid, the latter minimizing H-aggregate formation of the dye.Highlights► Molecular design of new indoline dye. ► Improvement of Jsc to show good zinc oxide cell performance. ► Decrease in H-aggregates formation in the presence of lithocholic acid.

Novel fluorescent mono- and bisboron complexes based on pyrimidine bearing β-iminoenolate ligands were synthesized, and their fluorescence properties were investigated. The nonsubstituted and trifluoromethyl-substituted monoboron complexes showed higher fluorescence quantum yield in solid state than in solution. The dimethylamino derivative of the monoboron complex exhibited positive solvatochromism in the fluorescence spectra. The bisboron complex showed significantly higher molar absorption coefficient and red-shifted maximum absorption and maximum fluorescence wavelengths than the corresponding monoboron complex.

Novel fluorescent dyes, thiazole–boron complexes bearing β-ketoiminate ligands, have been synthesized, and their fluorescence properties were investigated. The BF2 complexes showed a pronounced aggregation-induced emission enhancement effect because of the restriction of C–Ph intramolecular rotation. The BPh2 complexes showed higher fluorescence quantum yields than the corresponding BF2 complexes, both in solution and in the solid state.

A novel idoline dye, having dimethylfluorene-substituted indoline donor and dicyanovinylidene-introduced rhodanine acceptor (DN350), gave much higher efficiency than D205 due to bathochromic absorption band and prevention of aggregates formation.

A novel fluorescence dye based on pyrazine–boron complexes bearing a β-iminoketone ligand has been synthesized by using a simple two-step reaction. Synthesized complexes exhibited fluorescence in solution (Fmax: 472–604 nm) and in the solid state (Fmax: 496–624 nm). These complexes showed a larger Stokes shift (3690–4900 cm–1) than well-known boron dipyrromethene dyes (400–600 cm–1, in most cases).

The cell performance of novel benzoindoline dyes on zinc oxide prepared by template cathode electro-deposition method was compared with that of known indoline dyes. Among cyanoacrylic, single and double rhodanine acetic acid derivatives, the cyanoacrylic benzoindoline dye showed better performance than the indoline dye (D131) due to larger Jsc value which comes from its positive Eox level and bathochromic UV–vis absorption band.Highlights► The cell performance of novel benzoindoline dyes on zinc oxide prepared by template cathode electro-deposition method was compared with that of known indoline dyes. ► Only cyanoacrylic benzoindoline dye showed improved cell performance due to larger Jsc value. ► This could result from its positive Eox level and bathochromic UV–vis absorption band.

A fluorescent dye, the pyridomethene−BF2 complex, has been synthesized. Although pyridomethenes did not exhibit fluorescence, pyridomethene−BF2 complexes exhibited fluorescence both in solution and in the solid state. The trifluoromethyl-substituted BF2 complex formed a J-aggregate and showed the highest fluorescence quantum yield in the solid state among all pyridomethene−BF2 complexes.

The solar-light-to-electricity conversion efficiency of substituted indoline dyes depended on short-circuit photocurrent density which is affected by maximum incident photon-to-current efficiency. The oxidation potential of the double rhodanine indoline dyes needed to be >∼0.2 V vs Fc/Fc+ in acetonitrile to show high incident photon-to-current efficiency in a zinc oxide, dye-sensitized solar cell. To make a molecular design of highly efficient indoline dyes, the HOMO energy level should be more negative than ∼−4.9 eV by the DFT calculations.

In this study, we attempted to increase the fluorescence quantum yield of pyrromethene–BF2 complex (BODIPY) in the solid state by introducing bulky groups as substituents at the boron atom. Although the BF2 complex did not exhibit any fluorescence in the solid state (Φf = 0.00), the B(OMe)2, B(OPh)2, and BPh2 complexes did show solid-state fluorescence with quantum yields of 0.02, 0.04, and 0.22, respectively.

•Improved efficiency of benz[c,d]indolenine-based NIR squaraine dyes having germinal alkyl groups on another indolenine core.•Inhibition of aggregation formation on titanium oxide.•Inhibition of approaching I3− species to titanium oxide.•Improvement of conversion efficiency.Novel benz[c,d]indolenine-based unsymmetrical near-infrared squaraine dyes having germinal butyl (η = 0.55%) and octyl (η = 0.58%) groups at another indolenine ring exhibited higher conversion efficiency than the usually used methyl derivative (η = 0.38%). The germinal butyl and octyl groups can inhibit aggregation formation and approaching I3− species to improve the conversion efficiency.Novel benz[c,d]indolenine-based unsymmetrical near-infrared squaraine dyes having germinal butyl and octyl groups at another indolenine moiety exhibited higher conversion efficiency than the usually used methyl derivative, owing to less aggregate formation and inhibition of approaching I3− species on titanium oxide.

The synthesis and the solution/solid-state fluorescence properties of pyrimidine-based monoboron complexes differing in terms of the substituents [either two fluorine atoms (BF2 complex) or two phenyl groups (BPh2 complex)] on the boron atom are reported herein. Unrestricted C–Ar intramolecular rotation in the non-, trifluoromethyl-, and cyano-substituted derivatives resulted in negligible fluorescence in solution. On the other hand, methoxy- and dimethylamino-substituted analogues caused the restriction of the C–Ar intramolecular rotation and consequently resulted in relatively strong fluorescence in solution. The non-, trifluoromethyl-, and cyano-substituted derivatives showed a pronounced aggregation-induced emission enhancement effect. Dimethylamino-substituted derivatives exhibited solvatochromism in the fluorescence spectra. Substitution with BPh2 effectively enhanced the fluorescence quantum yield compared to the corresponding BF2 complexes in the solid-state.