UV Absorption Band Research Articles

Isonicotinic acid hydrazide-based silver nanoparticles as simple colorimetric sensor for the detection of Cr3+

A simple colorimetric method for the detection of Cr3+ is proposed using silver nanoparticles (AgNPs) prepared with isonicotinic acid hydrazide (INAH) and sodium citrate. The AgNPs were synthesized via a one-step approach at room temperature using INAH as reducing agent in the presence of sodium citrate. As synthesized AgNPs showed a characteristic UV absorption band at 403nm. The AgNPs exhibited an excellent response with regard to colorimetric sensing of Cr3+ as a result of their surface modification. No such response was observed in case of AgNPs prepared in the absence of INAH. It is proposed that INAH as isonicotinic acid (INA) and citrate on the surfaces of AgNPs interact cooperatively with the Cr3+ ions, resulting in aggregation of AgNPs in the solution. The aggregation induced by the addition of Cr3+ to the AgNPs containing solution leads to turn the color of a solution from golden yellow to red along with a remarkable change in absorption band. The color change was readily detectable with the naked eye even at lower concentration of Cr3+. The spectral change was monitored by UV–vis spectroscopy. Under optimized conditions, the sensor demonstrated a good linear relationship between absorption ratios and the Cr3+ concentrations in the range of 1×10−6 to 5×10−5M with correlation coefficient (R2) of 0.993, and detection limit of 4.5×10−7M for the colorimetric assay. In addition, the developed sensor showed high selectivity for Cr3+ in the presence of other common heavy metal ions. This method enabled the rapid determination of Cr3+ in tap and river water samples within the acceptable range of recoveries.

Syntheses and reductions of C-dimesitylboryl-1,2-dicarba-closo-dodecaboranes.

Two C-dimesitylboryl-1,2-dicarba-closo-dodecaboranes, 1-(BMes2)-2-R-1,2-C2B10H10 (1, R = H, 2, R = Ph), were synthesised by lithiation of 1,2-dicarba-closo-dodecaborane and 1-phenyl-1,2-dicarba-closo-dodecaborane, respectively, with n-butyllithium and subsequent reaction with fluorodimesitylborane. These novel compounds were structurally characterised by X-ray crystallography. Compounds 1 and 2 are hydrolysed on prolonged exposure to air to give mesitylene and boronic acids 1-(B(OH)2)-2-R-1,2-C2B10H10 (3, R = H, 4, R = Ph respectively). Addition of fluoride anions to 1 and 2 resulted in boryl-carborane bond cleavage to give dimesitylborinic acid HOBMes2. UV absorption bands at 318-333 nm were observed for 1 and 2 corresponding to local π-π*-transitions within the dimesitylboryl groups while visible emissions at 541-664 nm with Stokes shifts of 11 920-16 170 cm(-1) were attributed to intramolecular charge transfer transitions between the mesityl and cluster groups. Compound was shown by cyclic voltammetry to form a stable dianion on reduction. NMR spectra for the dianion [](2-) were recorded from solutions generated by reductions of 2 with alkali metals and compared with NMR spectra from reductions of 1,2-diphenyl-ortho-carborane 5. On the basis of observed and computed (11)B NMR shifts, these nido-dianions contain bowl-shaped cluster geometries. The carborane is viewed as the electron-acceptor and the mesityl group is the electron-donor in C-dimesitylboryl-1,2-dicarba-closo-dodecaboranes.

TD-DFT calculations of UV absorption bands and their intensities in the spectra of some tetrahydroquinolines

A detailed analysis of the MOs involved in the electronic transitions of 1-benzenesulfonyl-1,2,3,4-tetrahydroquinolines is presented for the first time.

Synthesis, and Optical and Electrochemical Properties of Germanium-Bridged Viologen

A Ge-bridged methylviologen derivative (GMV2+2I−) was synthesized by dimethylation of dipyridinogermole (DPyG). Viologen GMV2+2I− showed a UV absorption band at 270 nm, similar to DPyG and longer than the corresponding bridge-free methylviologen (MV2+2I−). Electrochemical properties of GMV2+2I− were investigated with respect to cyclic voltammograms, showing highly reversible two step reduction, like MV2+2I−. Interestingly, GMV2+2I− exhibited enhanced electron-affinity with higher 1st reduction potential by approximately 0.08 V than that of MV2+2I−, likely due to the effects Ge-bridge lowering the LUMO energy level. However, the 2nd potential was little affected by the bridge. Clear electrochromic colour changes based on the reversible electrochemical interconversion among GMV2+/GMV+/GMV were observed in acetonitrile. Monomethylated DPyG (GMV′+I−) was also prepared, whose properties are discussed in comparison with those of DPyG and GMV2+2I−.

The first UV absorption band for indole is not due to two simultaneous orthogonal electronic transitions differing in dipole moment.

The currently accepted model for the photophysics of indole assumes that the first UV absorption band encompasses two orthogonal electronic transitions ((1)Lb and (1)La), leading to two electronic states with a markedly different dipole moment. However, there is a body of evidence not explained by this model, which led us to develop a new photophysical model for indole. Based on the new model, the polarity of the electronic ground state (S0) in indoles is very similar to that of the first electronic excited state (S1) producing this structured emission; however, this excited state can lead to a highly dipolar excited state (S1') with largely structureless emission under the influence of the polarity of the medium, and also, very likely, of its viscosity. The molecular structure of the new excited state can be reversibly converted into the normal structure of the compound. Previous observations were confirmed by the absorption, emission, and excitation spectra for indole, as well as by its polarized emission and excitation spectra in various media. Thus, the polarized emission spectra for indole in glycerol at 283 K and 223 K showed the transition dipole moments for the emission from the first two excited states in a polar medium, S1 and S1', to differ by less than 20°.

Development of piperic acid derivatives from Piper nigrum as UV protection agents

Context: There is a need for the discovery of novel natural and semi-synthetic sunscreen that is safe and effective. Piperine has a UV absorption band of 230–400 nm with high molar absorptivity. This compound has a high potential to be developed to sunscreen.Objective: This study develops new UV protection compounds from piperine by using chemical synthesis.Materials and methods: Piperine was isolated from Piper nigrum L. (Piperaceae) fruits, converted to piperic acid by alkaline hydrolysis, and prepared as ester derivatives by chemical synthesis. The piperate derivatives were prepared as 5% o/w emulsion, and the SPF values were evaluated. The best compound was submitted to cytotoxicity test using MTT assay.Results: Piperic acid was prepared in 86.96% yield. Next, piperic acid was reacted with alcohols using Steglich reaction to obtain methyl piperate, ethyl piperate, propyl piperate, isopropyl piperate, and isobutyl piperate in 62.39–92.79% yield. All compounds were prepared as 5% oil in water emulsion and measured its SPF and UVA/UVB values using an SPF-290S analyzer. The SPF values (n = 6) of the piperate derivatives were 2.68 ± 0.17, 8.89 ± 0.46, 6.86 ± 0.91, 16.37 ± 1.8, and 9.68 ± 1.71. The UVA/UVB ratios of all compounds ranged from 0.860 to 0.967. Cytotoxicity of isopropyl piperate was evaluated using human skin fibroblast cells and the IC50 was equal to 120.2 μM.Discussion and conclusion: From the results, isopropyl piperate is an outstanding compound that can be developed into a UV protection agent.

Spectroscopic investigations on γ-irradiated Eu3+ and Dy3+ doped oxyfluoride glasses

Abstract Changes in the UV–visible spectra of undoped and Dy/Eu singly doped oxyfluoride glasses with varying PbF 2 /CdF 2 content were studied under high doses of gamma irradiation. The unirradiated undoped and doped glasses exhibited strong UV absorption and characteristic absorption bands due to the presence of rare earth ions. Gamma irradiation caused loss of transmission and red shift in the cut-off wavelength for the undoped and doped samples. The radiation induced absorption coefficient and energy band gap depicted variation due to the nature of rare earth as well as the host matrix. The rare earth addition affected the physical properties (density, refractive index, molar volume) and the structure of the studied glasses revealed by Fourier Transform Infrared Spectroscopy.

Photodissociation of OCS: deviations between theory and experiment, and the importance of higher order correlation effects.

The photodissociation of carbonyl sulfide (OCS) was investigated theoretically in a series of studies by Schmidt and co-workers. Initial studies [J. A. Schmidt, M. S. Johnson, G. C. McBane, and R. Schinke, J. Chem. Phys. 136, 131101 (2012); J. A. Schmidt, M. S. Johnson, G. C. McBane, and R. Schinke, J. Chem. Phys. 137, 054313 (2012)] found photodissociation in the first UV-band to occur mainly by excitation of the 2(1)A' (A) excited state. However, in a later study [G. C. McBane, J. A. Schmidt, M. S. Johnson, and R. Schinke, J. Chem. Phys. 138, 094314 (2013)] it was found that a significant fraction of photodissociation must occur by excitation of 1(1)A″ (B) excited state to explain the product angular distribution. The branching between excitation of the A and B excited states is determined by the magnitude of the transition dipole moment vectors in the Franck-Condon region. This study examines the sensitivity of these quantities to changes in the employed electronic structure methodology. This study benchmarks the methodology employed in previous studies against highly correlated electronic structure methods (CC3 and MRAQCC) and provide evidence in support of the picture of the OCS photodissociation process presented in [G. C. McBane, J. A. Schmidt, M. S. Johnson, and R. Schinke, J. Chem. Phys. 138, 094314 (2013)] showing that excitation of A and B electronic states both contribute significantly to the first UV absorption band of OCS. In addition, this study presents evidence in support of the assertion that the A state potential energy surface employed in previous studies underestimates the energy at highly bent geometries (γ ∼ 70°) leading to overestimated rotational energy in the product CO.

The effect of WO3 dopant on the structural and optical properties of ZnO–P2O5 glass and the effect of gamma irradiation

Zinc phosphate glasses doped with different ratios of tungsten trioxide were prepared. Optical and infrared absorption spectra were investigated before and after subjecting the glasses to 80kGy gamma ray dose. The base undoped zinc phosphate glass shows strong and broad UV absorption band centered at about 240nm but with no visible bands. The WO3-doped glasses reveal the same UV absorption bands beside extra three bands at 330, 380 and 575nm which are related to the presence tungsten ions in the pentavalent state. Infrared absorption spectra show characteristic variable phosphate groups with limited variations when introducing WO3 in the doping level up to 0.75%. Electron spin resonance measurements of the selected high doped tungsten glass indicate that mixed penta- and hexa-valent states of the tungsten ions and on gamma irradiation the pentavalent increases. The result supports the optical absorption after gamma irradiation which involves photochemical reactions in the UV region and the transformation of some W6+ to W5+ by absorbing electrons during the irradiation process.

Mapping the UV Photophysics of Platinum Metal Complexes Bound to Nucleobases: Laser Spectroscopy of Isolated Uracil·Pt(CN)4(2-) and Uracil·Pt(CN)6(2-) Complexes.

We report the first UV laser spectroscopic study of isolated gas-phase complexes of platinum metal complex anions bound to a nucleobase as model systems for exploring at the molecular level the key photophysical processes involved in photodynamic therapy. Spectra of the Pt(IV)(CN)6(2-)·Ur and Pt(II)(CN)4(2-)·Ur complexes were acquired across the 220-320 nm range using mass-selective photodepletion and photofragment action spectroscopy. The spectra of both complexes reveal prominent UV absorption bands (λmax = 4.90 and 4.70 eV) that we assign primarily to excitation of the Ur π-π* localized chromophore. Distinctive UV photofragmentation products are observed for the complexes, with Pt(IV)(CN)6(2-)·Ur photoexcitation resulting in complex fission, while Pt(II)(CN)4(2-)·Ur photoexcitation initiates a nucleobase proton-transfer reaction across 4.4-5.2 eV and electron detachment above 5.2 eV. The observed photofragments are consistent with ultrafast decay of a Ur localized excited state back to the electronic ground state followed by intramolecular vibrational relaxation and ergodic complex fragmentation.

UV absorption spectrum of the C2 Criegee intermediate CH3CHOO.

The UV spectrum of CH3CHOO was measured by transient absorption in a flow cell at 295 K. The absolute absorption cross sections of CH3CHOO were measured by laser depletion in a molecular beam to be (1.06 ± 0.09) × 10(-17) cm(2) molecule(-1) at 308 nm and (9.7 ± 0.6) × 10(-18) cm(2) molecule(-1) at 352 nm. After scaling the UV spectrum of CH3CHOO to the absolute cross section at 308 nm, the peak UV cross section is (1.27 ± 0.11) × 10(-17) cm(2) molecule(-1) at 328 nm. Compared to the simplest Criegee intermediate CH2OO, the UV absorption band of CH3CHOO is similar in intensity but blue shifted by 14 nm, resulting in a 20% slower photolysis rate estimated for CH3CHOO in the atmosphere.

Anisotropy and size effects on the optical spectra of polycyclic aromatic hydrocarbons.

The electronic and optical properties of polycyclic aromatic hydrocarbons (PAHs) present a strong dependence on their size and geometry. We tackle this issue by analyzing the spectral features of two prototypical classes of PAHs, belonging to D6h and D2h symmetry point groups and related to coronene as multifunctional seed. While the size variation induces an overall red shift of the spectra and a redistribution of the oscillator strength between the main peaks, a lower molecular symmetry is responsible for the appearance of new optical features. Along with broken molecular orbital degeneracies, optical peaks split and dark states are activated in the low-energy part of the spectrum. Supported by a systematic analysis of the composition and the character of the optical transitions, our results contribute in shedding light to the mechanisms responsible for spectral modifications in the visible and near UV absorption bands of medium-size PAHs.

Effects of charge transfer on the ESIPT process in methyl 5-R-salicylates.

The fluorescent behavior of the methyl-5-R-salicylates is analyzed in media of negligible acidity and basicity so that the methyl-5-R-salicylates may undergo solvent dipolarity changes or not in a controlled manner based on the following guidelines: (i) The molecular forms of these methyl-5-R-salicylates possessing an intramolecular hydrogen bond (IMHB) between their hydroxyl group and ether type oxygen (rotated tautomer) undergo no excited-state intramolecular proton transfer (ESIPT) in their first excited electronic state; (ii) on the other hand, the molecular species with an IMHB between its hydroxyl group and carbonyl oxygen (normal tautomer) exhibits both ESIPT and normal emission when charge transfer (CT) from the R-substituent to the phenol group is slight to moderate, but only normal emission is monitored when CT is strong. The special insensitivity of the first UV absorption band for the normal tautomer of methylsalicylate (MS, with R = H) to the polarity of the solvent is not echoed by the normal forms of methyl-5-R-salicylates containing substituents R with a substantial effect of CT in the IMHB of the compound. These solvatochromic features of MS are shared by the emissions of its derivatives. The photophysical evidence found for the methyl-5-R-salicylates confirms the photophysical model recently reported (Phys. Chem. Chem. Phys. 2012, 14, 8903-8909), which assigns three fluorescent emissions to the methyl-5-R-salicylates: two of them coming from the IMHB normal tautomer, which undergoes ESIPT, and another from the IMHB rotated tautomer, which cannot undergo ESIPT.

Effect of 3d-transition metal doping on the shielding behavior of barium borate glasses: A spectroscopic study

UV–visible and FT infrared spectra were measured for prepared samples before and after gamma irradiation. Base undoped barium borate glass of the basic composition (BaO 40%–B2O3 60mol.%) reveals strong charge transfer UV absorption bands which are related to unavoidable trace iron impurities (Fe3+) within the chemical raw materials. 3d transition metal (TM)-doped glasses exhibit extra characteristic absorption bands due to each TM in its specific valence or coordinate state. The optical spectra show that TM ions favor generally the presence in the high valence or tetrahedral coordination state in barium borate host glass.Infrared absorption bands of all prepared glasses reveal the appearance of both triangular BO3 units and tetrahedral BO4 units within their characteristic vibrational modes and the TM-ions cause minor effects because of the low doping level introduced (0.2%).Gamma irradiation of the undoped barium borate glass increases the intensity of the UV absorption together with the generation of an induced broad visible band at about 580nm. These changes are correlated with suggested photochemical reactions of trace iron impurities together with the generation of positive hole center (BHC or OHC) within the visible region through generated electrons and positive holes during the irradiation process.

Electronic state spectroscopy of diiodomethane (CH₂I₂): experimental and computational studies in the 30,000-95,000 cm⁻¹ region.

The electronic absorption spectrum of diiodomethane in the 30,000-95,000 cm(-1) region is investigated using synchrotron radiation; the spectrum in the 50,000-66,500 cm(-1) region is reported for the first time. The absorption bands in the 30,000-50,000 cm(-1) region are attributed to valence transitions, while the vacuum ultraviolet (VUV) spectrum (50,000-95,000 cm(-1)) is dominated by several Rydberg series converging to the first four ionization potentials of CH2I2 at 9.46, 9.76, 10.21, and 10.56 eV corresponding to the removal of an electron from the outermost 3b2, 2b1, 1a2, and 4a1 non-bonding orbitals, respectively. Rydberg series of ns, np, and nd type converging to each of the four ionization potentials are assigned based on a quantum defect analysis. Time dependent density functional theory calculations of excited states support the analysis and help in interpretation of the Rydberg and valence nature of observed transitions. Density functional theory calculations of the neutral and ionic ground state geometries and vibrational frequencies are used to assign the observed vibronic structure. Vibronic features accompanying the Rydberg series are mainly due to excitation of the C-I symmetric stretch (ν3) and CH2 wag (ν8) modes, with smaller contributions from the C-H symmetric stretch (ν1). UV absorption bands are assigned to low lying valence states 1(1)B2, 1(1)B1, 2(1)A1, 3(1)A1, 2(1)B1, and 2(1)B2 and the unusually high underlying intensity in parts of the VUV spectrum is attributed to valence states with high oscillator strength. This is the first report of a comprehensive Rydberg series and vibronic analysis of the VUV absorption spectrum of CH2I2 in the 50,000-85,000 cm(-1) region. The VUV absorption spectrum of CD2I2 which serves to verify and consolidate spectral assignments is also reported here for the first time.

Structural dynamics of phenylisothiocyanate in the light-absorbing excited states: Resonance Raman and complete active space self-consistent field calculation study

The excited state structural dynamics of phenyl isothiocyanate (PITC) after excitation to the light absorbing S2(A'), S6(A'), and S7(A') excited states were studied by using the resonance Raman spectroscopy and complete active space self-consistent field method calculations. The UV absorption bands of PITC were assigned. The vibrational assignments were done on the basis of the Fourier transform (FT)-Raman and FT-infrared measurements, the density-functional theory computations, and the normal mode analysis. The A-, B-, and C-bands resonance Raman spectra in cyclohexane, acetonitrile, and methanol solvents were, respectively, obtained at 299.1, 282.4, 266.0, 252.7, 228.7, 217.8, and 208.8 nm excitation wavelengths to probe the corresponding structural dynamics of PITC. The results indicated that the structural dynamics in the S2(A'), S6(A'), and S7(A') excited states were very different. The conical intersection point CI(S2/S1) were predicted to play important role in the low-lying excited state decay dynamics. Two major decay channels were predicted for PITC upon excitation to the S2(A') state: the radiative S(2,min) → S0 transition and the nonradiative S2 → S1 internal conversion via CI(S2/S1). The differences in the decay dynamics between methyl isothiocyanate and PITC in the first light absorbing excited state were discussed. The role of the intersystem crossing point ISC(S1/T1) in the excited state decay dynamics of PITC is evaluated.

Optical properties of crystals doped with Sm3+ or Dy3+ relevant to potential InGaN/GaN laser diode-pumped visible laser operation: A comparative study

Results of detailed spectroscopic investigation of Sm3+ and Dy3+ ions incorporated in crystal structures of Yal YAl3(BO3)4, LiNbO3, Gd3Ga5O12, Gd2SiO5, Lu2SiO5 and (Gd, Lu)2SiO5 are reported and discussed. The impact of the hosts on transition intensities and excited state relaxation dynamics of incorporated luminescent ions was examined. Distribution of luminescence intensity among spectral bands in terms of luminescence branching ratios was evaluated based on numerical integration of luminescence bands. Intensities of UV and blue absorption bands potentially useful for optical pumping were determined quantitatively in units of absorption cross section. The most intense luminescence bands related to potential laser transitions 4 G 5/2 → 6 H 7/2 of Sm3+ around 600 nm and 4 F 9/2 → 6 H 13/2 of Dy3+ around 580 nm were calibrated in units of emission cross section. Evaluated peak values of emission cross section range from 0.43 × 10−20 cm2 for Sm3+ in (Gd, Lu)2SiO5 to 1.17 × 10−20 cm2 for Sm3+ in LiNbO3. Those for dysprosium-doped crystals range from 0.63 × 10−20 cm2 for LiNbO3:Dy3+ to 2.0 × 10−20 cm2 for Yal YAl3(BO3)4:Dy3+. It follows from these considerations that samarium-doped crystals show promise for laser application owing to the combination of a strong absorption that matches radiation of commercial laser diodes emitting near 405 nm and long luminescence lifetime. Major shortcoming of dysprosium-doped crystals results from a weak intensity of absorption bands available for optical pumping near 450 nm and 385 nm combined with relatively strong self-quenching of luminescence.

Optical and FT Infrared spectral studies of vanadium ions in cadmium borate glass and effects of gamma irradiation

Combined optical and infrared absorption spectra of V2O5-doped cadmium borate glasses were investigated before and after gamma irradiation with a dose of 8 Mrad (=8×104 Gy). The undoped base cadmium borate glass reveals a spectrum consisting of strong charge transfer UV absorption bands which are related to the presence of unavoidable contaminated trace iron impurities (mainly Fe3+). The V2O5-doped glasses reveal an extra band at 380nm and the high V2O5-content glass also shows a further band at about 420nm. The observed optical spectrum indicates the presence of vanadium ions mainly in the pentavalent state (d0 configuration). The surplus band at 420nm shows that some trivalent vanadium ions are identified at high V2O5 content. The optical spectra of the glasses after gamma irradiation show small decrease of the intensity of the UV absorption which are interpreted by assuming the transformation of some Fe3+ ions by photochemical reactions with the presence of high content (45mol%) of heavy massive CdO causing some shielding behavior.FT infrared absorption spectra of the glasses show vibrational bands due to collective presence of triangular and tetrahedral borate groups in their specific wavenumbers. The FTIR spectra are observed to be slightly affected by both the V2O5-dopants being present in modifying low percent or gamma irradiation due to the presence of high content heavy CdO.

Electron dynamics in complex environments with real-time time dependent density functional theory in a QM-MM framework.

This article presents a time dependent density functional theory (TDDFT) implementation to propagate the Kohn-Sham equations in real time, including the effects of a molecular environment through a Quantum-Mechanics Molecular-Mechanics (QM-MM) hamiltonian. The code delivers an all-electron description employing Gaussian basis functions, and incorporates the Amber force-field in the QM-MM treatment. The most expensive parts of the computation, comprising the commutators between the hamiltonian and the density matrix-required to propagate the electron dynamics-, and the evaluation of the exchange-correlation energy, were migrated to the CUDA platform to run on graphics processing units, which remarkably accelerates the performance of the code. The method was validated by reproducing linear-response TDDFT results for the absorption spectra of several molecular species. Two different schemes were tested to propagate the quantum dynamics: (i) a leap-frog Verlet algorithm, and (ii) the Magnus expansion to first-order. These two approaches were confronted, to find that the Magnus scheme is more efficient by a factor of six in small molecules. Interestingly, the presence of iron was found to seriously limitate the length of the integration time step, due to the high frequencies associated with the core-electrons. This highlights the importance of pseudopotentials to alleviate the cost of the propagation of the inner states when heavy nuclei are present. Finally, the methodology was applied to investigate the shifts induced by the chemical environment on the most intense UV absorption bands of two model systems of general relevance: the formamide molecule in water solution, and the carboxy-heme group in Flavohemoglobin. In both cases, shifts of several nanometers are observed, consistently with the available experimental data.

Low-Bandgap Conjugated Polymers for Bulk Heterojunction Solar Cells

Polymer solar cells (PSCs) have drawn much attention for applications in renewable energy because of their potential for low cost, lightweight, and large-area processability. On the basis of bulk heterojunction (BHJ) concept using blends of p-type semiconducting polymers and n-type semiconducting fullerenes, device performances have been improved rapidly. Low-bandgap conjugated polymers have been developed intensively in recent years with the aim of better matching between the absorption and solar spectra, reaching a power conversion efficiency (PCE) more than 7%. On the other hand, [6,6]-phenyl-C61-butyric acid methyl ester ([60]PCBM) and its corresponding C70 derivative ([70]PCBM) are exclusively employed as an acceptor in the highly efficient PSCs. A facile method to control HOMO−LUMO levels of polymers by combining electron-rich (donor) and electron-deficient (acceptor) moieties in their repeating units, forming internal donor−acceptor (D−A) structures, has been intensively explored. Among the numerous building blocks, carbazole is one of the most prevalent electron-rich units owing to its fully aromatic fused ring with sufficient chemical and environmental stability. Various electron-deficient fused-heteroarenes were systematically copolymerized with 2,7-carbazole toward rational design of photovoltaic conjugated polymers by Leclerc et al. in 2008. They found that the HOMO and LUMO energy levels are mainly correlated to carbazole and acceptor units, respectively, and symmetric acceptor units allow for a higher degree of crystalline order. In their study, poly[N-9’-heptadecanyl-2,7-carbazole-alt-5,5-(4’,7’-di-2-thienyl-2’,1’,3’-benzothiadiazole)] (PCDTBT) with a relatively low HOMO level (−5.5 eV) had superior potential for applications in PSCs. The initial PCE reached 3.6% in a typical BHJ device and has been subsequently improved, exceeding 6% by thickness optimization and nanomorphology control of the BHJ layer. However, the bandgap of PCDTBT is still larger than the value (1.5 – 1.7 eV) of the ideal polymers for PCE values exceeding 10%. Recently, to lower the bandgap of PCDTBT without sacrificing the low HOMO level, further different electron-accepting monomers including phenylbenzotriazole, naphthothiadiazole, dialkoxylated benzothiadiazole, and quinoxaline-based units have been incorporated into 2,7-carbazole based copolymers. In addition, ladder-typed analogues of carbazole with forced planarity were copolymerized with benzothiadiazole unit. However, the PCE values of the PSCs with these polymers still remain at most comparable to PCDTBT-based devices.To investigate the effect of fluorine substitution on molecular and film structures, optical, electrochemical, and photovoltaic properties of a low-bandgap polymer, PCDTBT with deep HOMO energy level, a fluorinated analogue of PCDTBT (i.e., PCDTBT-F) has been developed for the first time by replacing two hydrogen atoms on benzothiadiazole (BT) units with two fluorine atoms. An analogous polymer, PCBBBT-F with additional hexylthiophenes between the thiophene and carbazole of PCDTBT-F has also been prepared to overcome the poor solubility of PCDTBT-F. The PCBBBT-F film showed wide absorption bands in UV and visible regions with an optical bandgap of 1.82 eV that is smaller than that of PCDTBT (1.89 eV), whereas the film of PCDTBT-F exhibited blue-shifted absorption with a bandgap of 1.96 eV due to the low molecular weight arising from the deficient solubility. The HOMO energy level of PCDTBT-F is lower than that of PCDTBT owing to the electron-withdrawing fluorination of the BT unit, whereas PCBBBT-F exhibited a higher HOMO level than PCDTBT, implying that the additional incorporation of electron-donating hexylthiophenes negated the fluorination effect. A BHJ-PSC that employed PCDTBT-F or PCBBBT-F as an electron donor and a fullerene derivative [70]PCBM as an electron acceptor yielded lower PCEs of 1.29% and 1.98%, respectively, than that of PCDTBT (6.16%) due to the unfavorable film structures of PCDTBT-F:[70]PCBM resulted from the poor solubility and low molecular weight as well as low crystallinities and limited exciton lifetimes of the fluorinated polymers. These results provide valuable information on the elaborate design of PCDTBT-based polymers for the PSC applications. I will also talk about other examples of low-bandgap conjugated poymers, especially phophole-based ones for BHJ solar cells.1-6 [1] T. Umeyama, K. Hirose, K. Noda, K. Matsushige, T. Shishido, Y. Matano, N. Ono, and H. Imahori, J. Phys. Chem. C, 116, 1256 (2012).[2] T. Umeyama, K. Hirose, K. Noda, K. Matsushige, T. Shishido,. H. Saarenpää, N. V. Tkachenko,. H. Lemmetyinen,. N. Ono, and H. Imahori, J. Phys. Chem. C, 116, 17414 (2012).[3] T. Umeyama, Y. Watanabe, M. Oodoi, D. Evgenia, T. Shishido, and H. Imahori, J. Mater. Chem., 22, 24394 (2012).[4] V. Manninen, M. Niskanen, T. I. Hukka, F. Pasker, S. Claus, S. Höger, J. Baek, T. Umeyama, H. Imahori, and H. Lemmetyinen, J. Mater. Chem. A, 1, 7451 (2013).[5] T. Umeyama, Y. Watanabe, E. Douvogianni, and H. Imahori, J. Phys. Chem. C, in press.[6] Y. Matano, H. Ohkubo, T. Miyata, Y. Watanabe, T. Umeyama, and H. Imahori, Eur. J. Inorg. Chem., in press.