Optoelectronic properties of naphthalene bis-benzimidazole based derivatives and their photovoltaic applications

Comparative Study of Bis-Schiff Case Containing Conjugated Oligomers Based on Phosphate and Silane Moieties: Investigation of Photophysical and Thermal Properties

Oligo(azomethine)s bearing phosphate and silane moieties were the subject of an investigation within this study. The initial stage involved the synthesis of two Schiff base monomers, denoted as SCH-1 and SCH-2 (SCHs), each possessing a pair of hydroxyl functional groups. This was achieved through a loss of water between the aldehyde and diamine precursors. Subsequently, the Schiff base entities were subjected to oligomerization through HCl-mediated elimination due to the interaction between the hydroxyl groups of the Schiff bases and the chlorine moieties of dichlorodiethylsilane (Si) or phenyl dichlorophosphate (P). This procedure yielded distinct P-oligo(azomethine) (P1-P, P2-P) and Si-oligo(azomethine) (P1-Si and P2-Si) structures corresponding to each precursor. The molecular structures of the synthesized Schiff base monomers and oligo(azomethine)s were elucidated employing Fourier transform infrared, 1H NMR, and 13C NMR techniques. Thermal properties of the resulting products were assessed by utilizing thermogravimetric analysis (TG-DTG/DTA and DSC) techniques. Scanning electron microscopy (SEM) was employed to acquire high-resolution images and detailed surface information on the samples. Additionally, X-ray diffraction was employed to analyze the phase properties of the solid samples. Furthermore, the optical band gap (E g) values of the resulting P-oligo(azomethine)s and Si-oligo(azomethine)s were determined utilizing UV-vis spectrophotometer. The relatively low band gap values exhibited by the synthesized oligo(azomethine)s were indicative of their potential suitability as semiconductive materials in the realm of electronic and optoelectronic device fabrication. Photoluminescence (PL) measurements disclosed a green emission profile upon excitation by blue light. The oligo(azomethine)s incorporating methoxy groups demonstrated a red shift in comparison to their counterparts with methyl groups. Remarkably, no discernible fluctuations in fluorescence were observed over a 3600 s interval under consistent conditions. This observation underscored the inherent stability of the PL emission across the spectral range of exciting light. Thermal analyses unveiled high thermal stability of the synthesized oligo(azomethine)s, sustaining their structural integrity up to 220 °C. The char % of P-oligo(azomethine)s and Si-oligo(azomethine)s were observed to fall within the range of 29.45-55.47% at 1000 °C. SEM images revealed the absence of pores on the surface of P2-Si, which exhibited the highest limiting oxygen index and thermal heat release index (T HRI) values.

The novel non-fully-fused ring small molecule acceptors: End-capped modification investigation

End-capped modification is an efficacious strategy for developing high-performance acceptor materials. In this paper, the experimentally synthesized A-D-A'-D-A type non-fully-fused ring acceptor IDTBT-4F (R) was used as a reference molecule, and five small molecule acceptors for R1-R5 were investigated by changing R's terminal functional groups. By using DFT/B3PW91/6-31G (d,p) method, the ground-state structures of all molecules were studied. The absorption spectra of these acceptors were gained by the TD-DFT/MPW1PW91/6-31G (d,p) approach. Meanwhile, the charge density difference and transition density matrix were analyzed effectively. It can be observed that, compared to the R molecule, all developed molecules exhibited narrower energy gaps, larger absorption wavelengths, more red-shifted absorption spectra, lower excitation energies, higher dipole moment and greater electron-accepting capacity. The strategy of functional group substitution is superior to halogen substitution in improving the aforementioned parameters. Both terminal π-extension and end-group chlorination strategies can synergistically enhance molecular performance. In addition, we also calculated the electron mobility of the dimers constructed by all the molecules, among which R1 and R4 molecules designed with -COOCH3 functional group substitution and R2 molecule with terminal chlorination achieved superior electron mobility compared to R molecule due to their significant electronic coupling. Overall, the study shows that the designed molecules can be highly effective candidates for applications of organic solar cells.

Effect of tailoring π-linkers with extended conjugation on the SJ-IC molecule for achieving high VOC and improved charge mobility towards enhanced photovoltaic applications

The problem of low efficiency of organic solar cells can be solved by improving the charge mobility and open circuit voltage of these cells. The current research aims to present the role of π-linkers, having extended conjugation, between the donor and acceptor moieties of indacenodithiophene core-based A-π-D-π-A type SJ-IC molecule to improve the photovoltaic performance of pre-existing SJ-IC. Several crucial photovoltaic parameters of SJ-IC and seven newly proposed molecules were studied using density functional theory. Surprisingly, this theoretical framework manifested that the tailoring of SJ-IC by replacing its π-linker with linkers having extended π-conjugation gives a redshift in maximum absorption coefficient in the range of 731.69-1112.86 nm in a solvent. In addition, newly designed molecules exhibited significantly narrower bandgaps (ranging from 1.33 eV to 1.93 eV) than SJ-IC having a bandgap of 2.01 eV. Similarly, newly designed molecules show significantly less excitation energy in gaseous and solvent phases than SJ-IC. Furthermore, the reorganization energies of DL1-DL7 are much lower than that of SJ-IC, indicating high charge mobility in these molecules. DL6 and DL7 have shown considerably improved open circuit voltage (VOC), reaching 1.49 eV and 1.48 eV, respectively. Thus, the modification strategy employed herein has been fruitful with productive effects, including better tuning of the energy levels, lower bandgaps, broader absorption, improved charge mobility, and increased VOC. Based on these results, it can be suggested that these newly presented molecules can be considered for practical applications in the future.

Design new organic material based on triphenylamine (TPA) with D-π-A-π-D structure used as an electron donor for organic solar cells: A DFT approach

Because of the increasing scarcity of fossil fuels and the growing need for energy, it has become necessary to research new renewable energy resources. In this study, five new high-performance materials (TP-FA₁F-TP - TP-FA₅F-TP) of the D-π-A-π-D configuration based on triphenylamine (TPA) were theoretically investigated by applying DFT and TD-DFT methods for future application as heterojunction organic solar cells (BHJ). The influence of the modification of the acceptor (A) of the parent molecule TP-FTzF-TP on the structural, electronic, photovoltaic and optical properties of the TP-FA1F-TP - TP-FA5F-TP organic molecules was investigated in detail. TP-FA₁F-TP - TP-FA₅F-TP showed E_gap in the interval of 1.44-2.01 eV with λ_abs in the range of 536-774 nm, open-circuit voltage (V_oc) values varied between 0.3 and 0.56 V and power conversion efficiencies (PCE) ranging from (3-6) %. Our results also show that the donor molecules suggested in this research exhibit an improved performance compared to the recently synthesized TP-FTzF-TP, such as a lowest HOMO energy, a smaller E_gap, and a greater absorption spectrum, and can lead to higher performance. Indeed, this theoretical research could lead to the future synthesis of better compounds as active substances used in BHJ.

Naphthalene and its Derivatives: Efficient Fluorescence Probes for Detecting and Imaging Purposes

Naphthalene, white crystalline solid having polycyclic aromatic hydrocarbon with characteristic mothball order is naturally present in crucial oils of various plants. Naphthalene derivatives are extensive drug resources and are use as wetting agents, surfactants and as insecticides. These derivatives exhibit unique photo physical and chemical properties. These characteristics make them the most studied group of organic compounds. Naphthalene dyes have rigid plane and large π-electron conjugation. Therefor they have high quantum yield and excellent photostability. Naphthalene based fluorescence probes due to hydrophobic nature exhibit excellent sensing and selectivity properties towards anions and cations and also used as a part of target biomolecules. In conjugated probe system, introducing naphthalene moiety caused improvement in photo-stability. Therefore among various conjugated framework, naphthalene derivatives are considered excellent candidate for the construction of organic electronic appliances. These derivatives are useful for a variety of applications owing to their strong fluorescence, electroactivity and photostability. This article is based upon investigation of photophysical properties of naphthalene derivatives and fluorescence detecting probe of naphthalene. For photophysical properties the techniques under investigation are UV visible spectroscopy and fluorescence spectroscopy. Concentration dependent spectra and solvatochromic shifts on UV visible spectra are also part of discussion.

New organic dye-sensitized solar cells based on the D-A-π-A structure for efficient DSSCs: DFT/TD-DFT investigations

Global energy consumption has increased due to population growth and economic development. Solar energy is one of the most important renewable energy sources for human consumption. In this research, four novel organic dyes (D2-D5) of the D-A-π-A structure based on triphenylamine (TPA) were studied theoretically using DFT and TD-DFT techniques for future usage as dye-sensitized solar cells (DSSCs). The effects of modifying the π-spacer of the reference molecule D1 on the structural, electronic, photovoltaic, and optical characteristics of the D2-D5 dyes were studied in detail. D2-D5 exhibited band gaps (E _gap) in the range from 1.89 to 2.10 eV with λ _abs in the range of 508 to 563 nm. The results obtained show that modifying the π-spacer of the dye D1 increased its hole injection and reinforced the intramolecular charge-transfer (ICT) impact, which resulted in a red-shifted ICT absorption with a greater molar extinction coefficient. The theoretically calculated open-circuit voltage (V _oc) values ranged from 0.69 to 1.06 eV, while the light-harvesting efficiency (LHE) values varied from 0.95 to 0.99. Indeed, this theoretical research could guide chemists to synthesize effective dyes for DSSCs.