Bay Functionalized Perylenediimide with Pyridine Positional Isomers: NIR Absorption and Selective Colorimetric/Fluorescent Sensing of Fe<Superscript>3+</Superscript> and Al<Superscript>3+</Superscript> Ions

Bay functionalized perylene diimide substituted with pyridine isomers, (2-pyridine (2HMP-PDI), 3-pyridine (3-HMP-PDI) and 4-pyridine (4-HMP-PDI)) have been synthesized and explored for selective coloro/fluorimetric sensing of heavy transition metal ions. HMP-PDIs showed strong NIR absorption (760–765 nm) in DMF. The absorption and fluorescence of HMP-PDIs have been tuned by make use of pyridine isomers. Reddish-orange color was observed for 2-HMP-PDI (λ_max = 437, 551, 765 nm) whereas 4-HMP-PDI exhibited light green (λ_max = 432, 522, 765 nm). 3-HMP-PDI showed orange-yellow (λ_max = 431, 524, 762 nm). The fluorescence spectra of 2-, 3- and 4-HMP-PDI showed λ_max at 585, 538, 546 nm, respectively. Interestingly, HMP-PDI dyes showed selective color change (intense pink color) and fluorescence quenching for Fe³⁺ and Al³⁺ metal ions in DMF. Absorbance spectra revealed complete disappearance of NIR absorption and intensification/appearance of new peak at lower wavelength. The concentration dependent studies suggest that 4-HMP-PDI can detect up to 36.52 ppb of Fe³⁺ and 43.12 ppb of Al³⁺ colorimetrically. The interference studies in presence of other metal ions confirmed the good selectivity for Fe³⁺ and Al³⁺. The mechanistic studies indicate that Lewis acidic character of Fe³⁺ and Al³⁺ ions were responsible for selective color change and fluorescence quenching.     

Spectral Investigations of Solvatochromism and Preferential Solvation on 1,4-Dihydroxy-2,3-Dimethyl-9,10-Anthraquinone

Solvatochromic and preferential solvation of 1,4-dihydroxy-2,3-dimethyl-9,10-anthraquinone (DHDMAQ) have been investigated using optical absorption and fluorescence emission techniques. Optical absorption spectra of DHDMAQ in different solvents show the intra molecular charge transfer band in the region 400–550nm. The observed blue shift with solvent polarity indicates the delocalisation of the excited state, owing to reduction in quasiaromaticity of the chelate rings formed by intra molecular hydrogen bonds, due to electrostatic or hydrogen bonding interaction. This is also confirmed by the observed low oscillator strength and the transition dipole moment. The observed quantum yield of DHDMAQ in different solvents is due to the inter molecular hydrogen bond in the excited state in addition to the intra molecular hydrogen bond. It also reveals from the low oscillator strength, which indicates that the radiative decay is low. Excited state dipole moment of DHDMAQ is calculated by solvatochromic data and it shows a lower value than ground state dipole moment. The preferential solvation parameter shows that in dimethyl formamide (DMF) + ethanol mixture, the DHDMAQ is preferentially solvated by ethanol in DMF rich region and by DMF in ethanol rich region. In the case of DMF + dichloromethane mixture DHDMAQ is preferentially solvated by DMF.     

Solvatochromic Studies of Fluorescein Dianion in N,N-Dimethylformamide/Water and Dimethylsulphoxide/Water Mixtures

Abstract

The absorption, excitation and fluorescence spectra of the fluorescein dianion (FL^2?) in N, N-Dimethylformamide (DMF)/water (H₂O) and Dimethylsulphoxide (DMSO)/H₂O solvent mixtures have been investigated. It is found that the absorption λ_max and emission maxima EX, _nax are both hypsochromic shifted when the H₂O content in the solvent mixtures increases. However, the shoulder peaks λ_s remain constant at 483. 5nm within the range of H₂O mole fraction, x= 0 to 0. 518 in a DMF/H₂O solvent mixture and at 484. 4nm within the range, x=0 to 0. 304, in a DMSO/H₂O mixture. Further increases in H₂O content, cause a hypsochromic shift in λ_s. The molar energies for the electronic transition from the ground state (S₀) to S₁, the first excited singlet state, (E_T(1)) and to S₂, the 2nd excited singlet state, (E_T(2)) of FL^2?in the solvent mixtures are also plotted against x. Linear straight lines and intersection points are observed at x=0. 73 for E_T(1) and at x=0. 51 for E_T(2) in the DMF/H₂O mixture and at x=0. 71 for E_T(1) and at x=0. 31 &; 0. 69 for E_T(2) in the DMSO/H₂O mixture. Hydrogen-bonding stabilization effects are used to explain the above observations. The variation in relative fluorescence quantum yields of S₁ and S₂ of FL^2? with x in the aprotic solvent-H₂O mixtures to FL^2? in pure aprotic solvent are determined and discussed.     

Solvatochromic and Preferential Solvation Studies on Schiff Base 1,4-Bis(((2-Methylthio)Phenylimino)Methyl) Benzene in Binary Liquid Mixtures

The solvatochromic behavior of the 1,4-bis(((2-methylthio) phenylimino)methyl) benzene [BMTPMB] in single solvents and binary mixtures were investigated. Fluorescence spectra show the dual emission due to twisted intramolecular charge transfer (TICT) state. The preferential solvation parameters: local mole fraction, X₂^L, solvation index δ_s2, exchange constant K₁₂ were calculated for the binary mixtures, ACN+MEOH, DMSO+CCl₄ and CCl₄+1,2 DCE. The dipole moment ratios between ground and excited states were deduced using the solvatochromic shifts of absorption and fluorescence spectra as a function of dielectric constant (ε), refractive index (n) and it was found to be 1.25.     

Chlorine K X-ray absorption-edge structures of CIS-[Pt(NH3)2Cl2], trans-[Pt(NH3)2Cl2], trans-[Pd(NH3)2Cl2] and (NH4)2PdCl4

The K absorption-edge spectra of the ligand chlorine ion in square-planar complex compounds cis- and trans-[Pt(NH₃)₂Cl₂], trans-[Pd(NH₃)₂Cl₂], and (NH₄)₂PdCl₄ are reported and discussed in connection with the chlorine K absorption spectra of K₂PtCl₄ and K₂PdCl₄, reported previously. The observed chemical shift of a white line at the absorption threshold is interpreted in terms of the difference of the ligand-field splitting of electronic states for metal ions. The white line is attributed to the electronic transition from the Cl^? ls level to the lowest unoccupied antibonding molecular orbital (MO), which is specified by a $\text{MO}\text{b}{}_{\mathrm{1g}}\text{(σ}{}^1\text{)}$ in the square-planar complex with D_4h symmetry. The other absorption structures are regarded as continuum “shape resonances” of the outgoing electron trapped by the cage of the surrounding atoms. The effect of geometrical isomerism is found in the chlorine K absorption spectra of cis- and trans-[Pt(NH₃)₂Cl₂].     

Synthesis and fluorescence study of sodium-2-(4′-dimethyl-aminocinnamicacyl)-3,3-(1′,3′-alkylenedithio) acrylate

We synthesized two new compounds: Sodium 2-(4′-dimethyl-aminocinnamicacyl)-3,3-(1′,3′- ethyl- enedithio) acrylate (STAA-1) and Sodium 2-(4′-dimethyl-aminocinnamicacyl)-3, 3-(1′,3′-propylenedithio) acrylate (STAA-2). The maximum absorption of these compounds ranges from 460 to 520 nm with different molecular structures in different solvents. Meanwhile, the emission peak of these compounds arranges from yellow (510 nm) to red (605 nm). The emission spectra show red shift according to the strength of the hydrogen bonding property of the solvent. But the absorption spectra do not show clearly relationship with the strength of the hydrogen bonding property of the solvent. The Stoke shift of the compounds ranges from 42 to 102 nm. It changes in the following order, EtOH>H₂O>DMF, and STAA-1>STAA-2 in the same solvent. The fluorescent quantum yield of STAA-1 was measured to be 7.12% with quinine sulphate as the standard compound in ethanol. Furthermore, the relationship of the fluorescence of STAA-1 with pH (ranges form 4 to 14) in water (c=∼10⁻⁴) was studied to make sure that these compounds could be used as proton sensors.     

Temperature evolution of the intra-ion absorption spectra of (NH2(C2H5)2)2CoCl4 crystals in the region of their phase transitions

On the basis of spectroscopic studies of (NH₂(C₂H₅)₂)₂CoCl₄ crystals, the absorption bands corresponding to the internal electronic transitions in the Co²⁺ ion were identified. The values of the crystal field and Racah parameters were calculated. The temperature evolution of the absorption spectra of (NH₂(C₂H₅)₂)₂CoCl₄ crystals reveals the anomalies of their parameters at the points of phase transitions. The corresponding changes of the absorption spectra were discussed in terms of distortion of the metal-halogen complex. The temperature dependences of the absorption spectra of (NH₂(C₂H₅)₂)₂CoCl₄ crystals confirm the presence of the thermochromic phase transitions at 255 and 330?K.     

On the Photophysicochemical Properties of Selected Fluoroquinolones: Solvatochromic and Fluorescence Spectroscopy Study

The photophysicochemical properties of selected fluoroquinolones in different solvents of various physical properties, including polarity and hydrogen bonding ability, were investigated using steady state fluorescence spectroscopy. The solvent-dependant fluorescence emission spectra of selected fluoroquinolones, namely ciprofloxacin (CIPR) and enrofloxacin (ENRO), were employed to gain insights concerning its photophysicochemical properties of interests. Interestingly, fluorescence spectra of the selected drugs exhibited structured emission spectra in nonpolar solvents such as hexane, whereas unstructured spectra were observed in more polar solvents such as alcohols and water. Also, a notable bathochromic shift in $ \lambda_{{\max }}^{{em}} $ was observed in fluorescence spectra of both drugs with increasing solvent polarity that resulted in biphasic behavior upon applying the Lippert-Mataga correlation that correspond to general and specific solvent effects. Applying the Lippert-Mataga correlation to the fluorescence spectra of CIPR and ENRO in various solvents was employed to estimate the dipole moment difference between the ground and excited states of them, $ \Delta \mu \left( {{\mu_e} - {\mu_g}} \right) $ , where obtained results revealed the values of 9.4 and 16.2 Debye for the LE and ICT states of ENRO, respectively, and 8.0 and 16.2 Debye for the LE and ICT states of CIPR, respectively. Multiple linear regression analysis (MLRA) based on Kamlet-Taft equating was applied against absorption frequency (ν_abs), emission frequency (ν_em), Stokes shift (?ν), and fluorescence quantum yield (Φ_f), where obtained results revealed excellent correlation (R: 0.916–0.966) that are consistent with other results considering the effect of solvent polarizability, hydrogen bonding ability, and viscosity on the photophysicochemical properties of the studied fluoroquinolones.     

Spectrophotometric Study of Luminol in Dimethyl Sulfoxide–Potassium Hydroxide

The spectrophotometric study of luminol (LH₂) in dimethyl sulfoxide (DMSO), DMSO-water solutions, and alkaline DMSO and DMSO-water solutions has been done, focusing on the effect of the KOH additon on LH₂ absorption and fluorescence properties. The absorption spectra indicate an acid-base equilibrium, and the luminol dianion (L^2–) formation at 3 × 10^–4 – 2.4 × 10^–3 M KOH. The decrease of the fluorescence intensity and the variation of the excitation spectra of LH₂-DMSO-KOH solutions with KOH concentration have been similarly explained. The acid-base process is reversible. The addition of HCl to the solution with 3.0 × 10^–3 M KOH leads to an increase of the fluorescence intensity to its highest value, observed in pure DMSO. The addition of HCl to the LH₂-DMSO solution leads to the decrease of the fluorescence intensity as a result of the LH⁺ ₃ cation formation. In LH₂-DMSO-water, the fluorescence band is shifted from 405 nm to 424 nm and increased in the intensity. In the presence of KOH (in LH₂-DMSO-water-KOH solution) a new band appears, with the maximum at 485 nm and the band at 405 nm decreased. The changes in fluorescence lifetimes also evidence the different chemical species formed.     

Mesoporous silica-coated NaYF4:Yb3+, Er3+ particles for drug release

NaYF₄:Yb³⁺, Er³⁺ nanoparticles were successfully prepared by a polyol process using diethyleneglycol (DEG) as solvent. These NaYF₄:Yb³⁺, Er³⁺ nanoparticles can be coated with mesoporous silica using nonionic triblock copolymer EO₂₀PO₇₀EO₂₀ (P 123) as structure-directing agent and other materials. The composites can load ibuprofen and release the drug in the phosphate buffer solution (PBS). The composites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen absorption/desorption isotherms, fluorescence spectra, and UV/Vis absorption spectra, respectively. The composites have the mesoporous structure. In addition, the composites emit red fluorescence (from Er³⁺) under 980 nm near infrared laser excitation, which can be used as fluorescent probes in the drug-delivery system.     

甲胺水合离子团簇的结构模型及红外光谱研究

本文利用量子化学计算方法,研究了甲胺和水复合离子团簇[(CH₃NH₂)(H₂O)_n]⁺的几何结构、能量和红外光谱,揭示了结构生长模型、氢键作用机制和质子转移机理. 研究结果表明,在[(CH₃NH₂)(H₂O)_n]⁺团簇中,甲胺甲基上的一个氢原子转移到氨基上,形成分子内质子转移的CH₂NH₃⁺离子核心结构模型,水分子作为氢键受体,与质子化氨基NH₃⁺形成氢键. CH₃NH₂⁺离子核心结构模型没有CH₂NH₃⁺离子核心结构模型稳定. 在团簇的红外光谱中,CH振动、自由NH振动、氢键结合的NH振动和OH振动模式在CH₃NH₂⁺和CH₂NH₃⁺两种离子核心结构模型的理论计算红外光谱中明显不同,因此可用于鉴别甲胺水合离子团簇的结构模型,有助于理解甲胺和水复合团簇的氢键网络结构.     

Spectrophotometric and spectrofluorimetric investigation of different equilibria of a recently synthesized Schiff base with the aid of chemometric methods

In this study ground and excited states acidic dissociation constants of a recently synthesized Schiff base was obtained in a DMF:water mixture of 30:70 (v/v) using absorption and fluorescent spectra of the Schiff base in different pH values with the aid of chemometric methods. In addition, the fluorescent of the two kinds of tautomers of this Schiff base was investigated and the rate of tautomerization was obtained using rank annihilation factor analysis (RAFA). The effect of different kinds of surfactants such as sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB) and Triton X-100 on fluorescence spectrum of the Schiff base in a DMF:water mixture of 2:98 (v/v) was investigated. CTAB increased the fluorescence intensity of the Schiff base while SDS and Triton X-100 had no significant effect on it. β-Cyclodextrin increased the fluorescence intensity of the Schiff base. Also the sensing behavior of this Schiff base toward metal ions was studied in DMF and ethanol by fluorescence spectroscopy. The Schiff base showed prominent fluorescent signal in the presence of Zn²⁺, whereas other metal ions failed to induce response and ground-state dissociation constant of the complex was determined by direct fluorimetric titration as a function of Zn²⁺ concentration.     

Spectral characteristics and fluorescence quenching of N,N′-bis(4-pyridyl)-3,4:9,10-perylenebis(dicarboximide) (BPPD)

The photophysical properties such as electronic absorption, molar absorptivity, emission spectra, fluorescence quantum yield and fluorescence lifetime of N,N′-bis(4-pyridyl)-3,4:9,10-perylene bis(dicarboximide) (BPPD) have been measured in different solvents. Both electronic absorption and fluorescence spectra are not sensitive to medium polarity, while the fluorescence quantum yield (?_f) is solvent dependent. The ground state geometry has been computed by using density functional theory (DFT), the transition from HOMO to LUMO from perylene core with maximum absorption at 512 nm and HOMO–LUMO energy difference equal 2.53 eV. BPPD dye undergoes molecular aggregation to dimmer or higher aggregates in dimethyl sulfoxide (DMSO). Crystalline solids of BPPD gives excimer-like emission at 676 nm. The fluorescence quenching of BPPD is also studied using hydrated ferric oxide nanoparticle (FeOOH), and the Stern–Volmer rate constants (K_sv) were calculated as 8×10⁶ and 9.2×10⁶ M^?1 in ethanol and ethylene glycol, respectively.     

Excited-state hydrogen bonding effect on dynamic fluorescence of coumarin 102 chromophore in solution: A time-resolved fluorescence and theoretical study

The steady-state absorption and emission as well as the time-resolved fluorescence spectra of coumarin 102 (C102) in both aprotic and alcoholic solvents have been used to study the effect of excited-state hydrogen bond on the dynamic fluorescence of C102 chromophore in various solutions. The dual fluorescence of C102 in alcohols, which is dependent on the hydrogen-bonded donation ability of the solvent, has been assigned to the distribution of free C102 and a hydrogen-bonded complex. Furthermore, a shift of the fluorescence spectra induced by excited-state hydrogen bond has been demonstrated to take place within hundreds of picoseconds by the performance of the time-resolved fluorescence spectra with the time-correlated single-photon-counting (TCSPC) technique. Moreover, the time-dependent density functional theory (TDDFT) has been used to calculate the hydrogen-bonded equilibrium constant pK_HB in different electronic states. It has been demonstrated for the first time that the hydrogen bond strengthening in electronic excited states could decrease the free energy of the hydrogen-bonded complex due to its stronger binding energy. Therefore, the hydrogen-bonded equilibrium will become markedly in favor of the hydrogen-bonded forms in electronic excited states by comparison with the case in the ground state.     

Mössbauer effect studies on alkali tris (malonato) ferrates(III)

Mössbauer spectra of alkali tris(malonato) ferrates(III) i.e. M₃[Fe(C₃H₂O₄)₃].4H₂O(M=Li, Na, K, NH₄) at 298±2K display a single broad absorption band due to spin lattice relaxation effect. The isomer shift values indicate these complexes to be high spin with octahedral symmetry. The isomer shift shows a decreasing trend with the increase in electronegativity/polarizing power of the substituent cation (Li⁺, Na⁺, K⁺, NH₄ ⁺). A linear correlation between isomer shift values and the (Fe-O) stretching freguencies has also been observed.     

The photostability and fluorescence properties of diphenylisobenzofuran

The photostability and fluorescence properties of 1,3-diphenylisobenzofuran (DPBF), a popular singlet oxygen (¹O₂ or ¹Δ_g) trapping-agent used in various solvents, are examined by UV-vis absorption, steady-state and time-resolved fluorescence techniques, as well as laser flash photolysis. DPBF is found to be easily photolyzed even if it is only exposed to the weak daylight in halogen-containing solvents in the absence of singlet oxygen. The photolysis is due to the addition of •CCl₃ (•CHCl₂) to DPBF in the absence of oxygen, or •OOCCl₃ (•OOCHCl₂) initiated chain polymerization of DPBF in the presence of oxygen. This result suggests that the reported singlet oxygen production in these solvents detected by DPBF was significantly higher than the true value. DPBF in DMF, DMSO, etc., on the other hand, is stable enough to enable fluorescence measurements. The fluorescence quantum yield of DPBF is very high in aprotic solvents and close to unity. The absorption, excitation and emission maxima are only slightly affected by the nature of solvents. The fluorescence lifetime is 5.0±0.3 ns.     

Formation of Metallophthalocyanine Trimers in Liquid Solutions

For solutions of the complexes of phthalocyanine (PhC) with magnesium (Mg-PhC) and of tetrachloromethyl-PhC with zinc (Zn-PhCCh) in mixtures of glycerin with dimethyl formamide (DMF) and for Zn-PhCCh in toluene and DMF it has been found that the electron absorption spectra substantially depend on the substance concentration. It is shown that these changes are attributable to the association of the molecules of pigments. The number of molecules in the associates and the equilibrium constants for this association are determined. The formation of the trimers of Mg-PhC in binary solutions and the dimers of Zn-PhCCh in toluene, DNF, and binary solutions has been established. It has been found that on association the Q absorption bands of the pigments shift to shorter wavelengths as compared to the bands of the monomers. For the Mg-PhC trimers, the shift is = 1410 cm^–1, while for the Zn-PhCCh dimers it is 990 cm^–1 in toluene, 930 cm^–1 in DMF, and 925 cm^–1 in the mixture of DMF with glycerin. It is concluded that the structure of the trimers and dimers is of the type of a stack in which molecules are arranged in parallel one above the other at a distance of 3.5 to 4.0 Å between the planes of the molecules. In association, the fluorescence intensity of the pigments decreases substantially (the decrease corresponds to the decrease in the concentration of the monomer molecules of phthalocyanines), with the fluorescence spectra remaining unchanged. Consequently, the associates of the pigments do not display pronounced fluorescence.     

Fluorescence and absorption spectra of 9, 10-diazaphenanthrene solutions at 77°K

The S₁(n, √^*) ? S₀ fluorescence and absorption spectra of 9, 10-diazaphenanthrene solutions in hydrocarbons possess at 77°K a quasilinear structure (Shpolskii effect). In the frozen n-hexane matrix (c = 10^-4 M) the fluorescence spectrum displays a triplet structure (22 181, 22 169 and 22 149 cm^-1 for the O-O transition). The spectra of 9, 10-diazaphenanthrene solution are shifted towards the red compared with those of the single crystal (～ 900 cm^-1). A good agreement between the calculated and experimental values of this shift is obtained. A strong concentration effect on the structure of the spectra is discussed. A quasilinear structure is observed also in the second absorption band.     

Stilbene-Like Molecules as Fluorescent Probes Applied for Monitoring of Polymerization Process

2-(p-N,N-dimethylaminostyryl)benzoxazole (OS), 2-(p-N,N-dimethylaminostyryl)-benzothiazole (SS) and 2-(p-N,N-dimethylaminostyryl)naphtiazole (PS) were prepared and their absorption and fluorescence spectra were measured in various solvents at room temperature. On the basis of the solvatochromic behavior the ground state (μ_g) and excited state (μ_e) dipole moments of these pN,N-dimethylaminostyryl derivatives were evaluated. The dipole moments (μ_g and μ_e) were estimated from solvatochromic shifts of absorption and fluorescence spectra as function of the dielectric constant (ɛ) and refractive index (n) of applied solvents. The absorption spectra only slightly are affected by the solvent polarity in contrast to the fluorescence spectra that are highly solvatochromic and display a large Stokes shift. The analysis of the solvatochromic behavior of the fluorescence spectra as function of Δf (ɛ, n) revealed that the emission occurs from a high polarity excited state. The large dipole moment change along with the strongly red-shifted fluorescence, as the solvent polarity is increased, demonstrate the formation of an intramolecular charge transfer state (ICT). Compounds under the study were used as fluorescence probes for monitoring the kinetics of polymerization. The study on the changes in fluorescence intensity and spectroscopic shifts of studied compounds were carried out during thermally initiated polymerization of methyl methacrylate (MMA) and during photoinitiated polymerization of 2-ethyl-2-(hydroxymethyl)propane-1,3-diol triacrylate (TMPTA).     

Effects of hydrogen flow on properties of hydrogen doped ZnO thin films prepared by RF magnetron sputtering

The hydrogen doped ZnO (ZnO:H) thin films were deposited on quartz glass substrates by radio frequency magnetron sputtering. The doping characteristics of ZnO:H thin films with varied hydrogen flow ratio were investigated. At low hydrogen flow ratio (H₂/(H₂+Ar)≤0.02), the ZnO:H thin films exhibited dominant (002) peaks from X-ray diffraction and the lattice constants became smaller. The particles were mainly a columnar structure. The particles’ size became smaller, and the island-like structure appeared on the thin films surface. In addition, the low resistivity properties of ZnO:H thin films was ascribed to the increase of the carriers concentration and carriers mobility; When the hydrogen flow ratio was more than 0.02 (M≥0.02), two absorption bands at 1400–1800 cm^?1 and 3200–3900 cm^?1 were observed from the FT-IR spectra, which indicated that the ZnO:H thin films had typical Zn–H bonding, O–H bonding (hydroxyl), and Zn–H–O bonding (like-hydroxyl). The scanning electron microscope (SEM) results show that a large number of hydroxyl agglomeration formed an island-like structure on the thin films surface. The absorption peak at about 575 cm^?1 in the Raman spectra indicated that oxygen vacancies (V_O) defects were produced in the process of high hydrogen doping. In this condition, the low resistivity properties of ZnO:H thin films were mainly due to the increasing electron concentration resulted from V_O. Meanwhile, the Raman absorption peaks at approximately 98 cm^?1 and 436 cm^?1 became weaker, and the (002) XRD diffraction peak quenched and the lattice constants increased, which shows that the ZnO:H thin films no longer presented a typical ZnO hexagonal wurtzite structure. With the increasing of hydrogen flow ratio, the optical transmittance of ZnO:H thin films in the ultraviolet band show a clear Burstein–Moss shift effect, which further explained that electron concentration was increased due to the increasing V_O with high hydrogen doping concentration. Moreover, the optical reflectance of the thin films decreased, indicating the higher roughness of the films surface. It was noteworthy that etching effect of H plasma was obvious in the process of heavy hydrogen doping.