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In this work, we designed a series of butterfly type organic dyes, named ME07 - ME13 by introducing such as triphenylamine, phenothiazine, coumarin groups etc. as electron donors and further investigated their absorption spectra using density functional theory (DFT) and time-dependent DFT (TDDFT). All designed dyes cover the entire visible absorption spectrum from 300 to 800 nm. It's fascinating that ME13 molecule has two absorption peak and the molar coefficient of two absorption peaks are above 4.645 × 10 4 M −1 ·cm −1 . The light absorption area of ME13 exhibits an increment of 16.5–19.1% compared to ME07 - ME12 . Furthermore, we performed a detailed analysis on their geometrical and electronic properties, including molecular structures, energy levels, light harvesting efficiency (LHE), driving force (ΔG inject ), regeneration (ΔG regen ),electron dipole moments (μ normal ), intermolecular electron transfer and dye/(TiO 2 ) 38 system electron transitions. The results of calculation reveal that double coumarin donors in ME13 are promising functional groups for butterfly type organic dye sensitizers. It is expected that the design of double donors can provide a new strategy and guidance for the investigation in high efficiency dye-sensitized devices. [ABSTRACT FROM AUTHOR]

Based on the experimentally synthesized dye JZ145 , we designed a series of novel D-A-π-A dyes SPL201-SPL211 with different π-conjugated bridges and a new auxiliary withdrawing group for highly efficient dye-sensitized solar cells (DSSCs) using density functional theory (DFT) and time-dependent DFT(TDDFT). The molecular structures, energy levels, absorption spectra, light-harvesting efficiency (LHE), driving force of injection(ΔG inj ) and regeneration(ΔG reg ) , electron dipole moment (μ normal ) and lifetime of the first excited state(τ) were all scrutinized in details. Results reveal that the additional withdrawing group A2 and the π-conjugated group di-η-hexyl-substituted cyclopentadithiophene (CPDT) are more promising functional groups for the organic dyes with D-A-π-A structure. We further designed SPL212 and SPL213 by employing indoline group as donor, the above screened functional groups as π-conjugated bridge and additional withdrawing group, biscarbodithiolic acid and dicyanovinyl sulfonic acid groups as acceptor group. We found that SPL212 exhibits not only a higher molar extinction coefficient with an increment of 30.8%, larger excited state lifetime and an obvious redshift of 201 nm but also a broader absorption spectrum covering the entire visible range even up to near-IR of 1200 nm compared to JZ145 . So, SPL212 can be used as a promising candidate for DSSCs. In addition, the results also prove that biscarbodithiolic acid may be more favorable than dicyanovinylsulfonic acid as acceptor group in DSSCs. [ABSTRACT FROM AUTHOR]

Photocatalytic hydrogen production, capable of dissociating water to make hydrogen using sunlight as abundant and clean energy, provides a promising solution for energy crisis. However, currently dominated metal complexes photosensitizers are based on precious and rare metal elements, which prohibits large scale applications. Herein, based on the experimental dye Eosin Y (EY 2− ), we report a series of metal-free organic dyes EY 2- 1- EY 2- 18 and present a systematic study on their ground-state geometry, electrochemistry, energy gap, reduction potential and driving force by using density functional theory (DFT) and time-dependent DFT (TDDFT). The calculated results show that compared to other dyes, the dye EY 2- 11 has a large visible light absorption range, a higher reduction potential and greater driving force, which indicates that EY 2- 11 is a promising candidate for the visible-light-driven hydrogen production. Our theoretical researches are expected to provide valuable insights for designing efficient metal-free organic photosensitizers. [Display omitted] • The non-noble metal photocatalytic hydrogen production system was further constructed by designing organic photosensitizer. • Reasonable matching of hydrogen production system is helpful to the realization of high hydrogen production performance. • EY 2- 11 has better catalytic performance by visible light, which indicates that EY 2- 11 is a promising candidate. • Provide valuable insights for designing efficient organic photosensitizers. [ABSTRACT FROM AUTHOR]

Auxiliary acceptor groups play a crucial role in D-A-π-A structured organic dyes. In this paper, we designed three D-A-π-A structured organic molecules based on the prototype dye QT-1 , named ME18 – ME20 , and further investigated their electronic and optical properties with density functional theory (DFT) and time-dependent DFT (TDDFT). The calculated results indicate that the scope and intensity of dyes' absorption spectra have some outstanding changes by inserting auxiliary groups. ME20 has not only 152 nm redshifts to long wave orientation, but also 78% increased oscillator strength compared to QT-1 , and its absorption spectrum broadens region even up to 1400 nm. Then, we studied the reason that the effect of the introduced different auxiliary acceptor groups in these dyes through their ground states geometries and energy levels, electron transfer and recombination rate. [ABSTRACT FROM AUTHOR]

[Display omitted] It is very important to seek visible light photosensitizers with high catalytic activity and continuous reaction stability to promote the development of the homogeneous photocatalytic hydrogen production. The study shows that the hydrogen production activity of organic dyes is higher than that of noble metal complexes under the same experimental conditions, so the pure organic dyes can effectively reduce the hydrogen production reaction cost under the premise of ensuring the photocatalytic activity. In this work, we take rhodamine photosensitizers S150 to replace S in the xanthene ring as the prototype and modify its structure by extending side chain. We further comprehensively study the electronic and optical properties of newly designed photosensitizer molecules by density functional theory (DFT). The results indicate that both S156 and S162 molecules exhibit excellent light absorption properties, such as wide range of absorption spectrum and good visible light response. The molar extinction coefficient of S156 molecule is as high as 2.65 × 10 4 M - 1 · c m - 1 . And the molecules that are screened out have a larger photoinduced electron transfer drive and more negative reduction potential. The reduction potential of S162 (-0.76 V vs SCE) is 22.6 % higher than that of S150, which suggests that S162 has more outstanding photocatalytic performance of hydrogen production than S150. So the dyes extended by the 3-(methoxymethyl) Heptane side chain are very promising candidates for homogeneous photocatalytic hydrogen production photosensitizer systems. [ABSTRACT FROM AUTHOR]