Push-Pull Heterocyclic Dyes Based on Pyrrole and Thiophene: Synthesis and Evaluation of Their Optical, Redox and Photovoltaic Properties

Three heterocyclic dyes were synthesized having in mind the changes in the photovoltaic, optical and redox properties by functionalization of 5-aryl-thieno[3,2-b]thiophene, 5-arylthiophene and bis-methylpyrrolylthiophene π-bridges with different donor, acceptor/anchoring groups. Knoevenagel condensation of the aldehyde precursors with 2-cyanoacetic acid was used to prepare the donor-acceptor functionalized heterocyclic molecules. These organic metal-free dyes are constituted by thieno[3,2-b]thiophene, arylthiophene, bis-methylpyrrolylthiophene, spacers and one or two cyanoacetic acid acceptor groups and different electron donor groups (alkoxyl, and pyrrole electron-rich heterocycle). The evaluation of the redox, optical and photovoltaic properties of these compounds indicate that 5-aryl-thieno[3,2-b]thiophene-based dye functionalized with an ethoxyl electron donor and a cyanoacetic acid electron acceptor group/anchoring moiety displays as sensitizer for DSSCs the best conversion efficiency (2.21%). It is mainly assigned to the higher molar extinction coefficient, long π-conjugation of the heterocyclic system, higher oxidation potential and strong electron donating capacity of the ethoxyl group compared to the pirrolyl moiety.

Exploring Orthogonality between Halogen and Hydrogen Bonding Involving Benzene

The concept of orthogonality between halogen and hydrogen bonding, brought out by Ho and coworkers some years ago, has become a widely accepted idea within the chemists’ community. While the original work was based on a common carbonyl oxygen as acceptor for both interactions, we explore here, by means of M06-2X, M11, ωB97X, and ωB97XD/aug-cc-PVTZ DFT calculations, the interdependence of halogen and hydrogen bonding with a shared π-electron system of benzene. The donor groups (specifically NCBr and H2O) were placed on either or the same side of the ring, according to a double T-shaped or a perpendicular geometry, respectively. The results demonstrate that the two interactions with benzene are not strictly independent on each other, therefore outlining that the orthogonality between halogen and hydrogen bonding, intended as energetical independence between the two interactions, should be carefully evaluated according to the specific acceptor group.

Fast Reverse Intersystem Crossing Over 107 s-1 in Organic Emitters with Inverted Singlet-Triplet Gap via Intramolecular Through Space Charge Transfer

Controlling excited state properties to achieve fast reverse intersystem crossing rates of over 107 s-1 is still challenging for intramolecular through-space charge transfer (TSCT) based delayed fluorescent materials. To gain further insight into the relationship between through-space and through-bond charge transfer (TSCT/TBCT), herein, three compounds DPS-24Ac, DPS-25Ac and DPS-OAc were prepared and characterized via NMR, MS and single crystal, in which the diphenylsulfone (DPS) is used as the acceptor group and acridine (Ac) as the donor moiety. Intense emissions from blue to yellow with high emission efficiency of 70-100% are detected for all emitters. Both computations and experiments suggest that compounds DPS-24Ac and DPS-25Ac have a clear TSCT effect and also an inverted adiabatic singlet-triplet gap which can be explained by the kinetic exchange mechanism. Notably, compound DPS-24Ac achieves the highest reverse intersystem crossing rate constant (krISC) of over 107 s-1 via manipulation of both TSCT and TBCT effects. The solution-processed devices display maximum external quantum efficiencies of 21.73, 12.14 and 4.96% for DPS-24Ac, DPS-25Ac and DPS-OAc, respectively. Overall, this work provides a novel avenue to achieve highly-efficient OLED materials with fast rISC by controlling both TSCT and TBCT effects.

Improving the electrical and optical properties of C50 fullerene using the Donor-Acceptor groups

In this research, the C50 fullerene was employed as the source of the π electrons and the electron donor-acceptor groups were used to enhance its optical properties. Considerable enhancement in its electronic and optical property of as the result of donor and acceptor group presence was observed. For instance, in UV-Visible absorption spectrum, the number of absorption lines significantly increase which may be the relaxation of the electronic transition selection rules. Considerably, the substituted forms of C50, has numbers of absorption bands in near infrared region. The BH2–C50-NCH3Li and NO–C50-NCH3Li molecules have superior improvement in optical properties. Finally, the donor and acceptor groups influence on non-linear optical properties (NLO) of C50 were explored and the considerable improvement in NLO properties of C50 was observed which the NLO improvements for BH2-C50-NCH3Li and NO-C50-CH2Li cases is higher than others.

Acceptor Modified Influence on Tetrahydroquinoline Efficient Chromophores for Optoelectronic Properties - A First Principle Study

In this study, a theoretical investigation of the photoinduced charge transfer (CT), electron injection, regeneration and Non-linear optical (NLO) of the A1-A4 structures were carried out for optoelectronic applications based on tetrahydroquinoline (C1-1) dye. Besides, a detailed assessment of the association among the electronic structures, chemical hardness, spectral and photovoltaic (PV) presentation were defined in DSSCs. Furthermore, this exploration purposes improved the electron-injection procedure, as well as the light-harvesting efficiency (LHE) of the dyes. For the research purpose, PO3H2, CONHOH, SO2H and OH (A1-A4) chromophores effects among the tetrahydroquinoline moieties related via a thiophene group were used as the electron acceptor group. The density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations were executed on the designing dye molecules. The presentation of three functional groups (Becke’s three-parameter and Lee-Yang-Parr (B3LYP), coulomb-attenuating method-B3LYP (CAM-B3LYP) and Head-Gordon model (ωB97XD) were analyzed maximum absorption peak for C1-1. Here, TD-ɷB97XD with the 6-31G(d) combined functional and basis set were provided reliable effects to the C1-1. Therefore, newly designed A1-A4 dyes in absorption spectra were followed by TD-ɷB97XD method. Among these results, A1 dye displays red-shift and higher molar extinction coefficient than the other dyes and C1-1. It is specified that the PO3H2 have better PV properties, compared to literature. The NLO belongings of the A1-A4 sensitizers were derived in the polarizability and first-order hyperpolarizability. The calculated value of A1 dye has best for NLO presentation. The theoretically outcomes were intensely recommended that molecular proposal of the sensitizer has a vital role for the optoelectronic properties.

meta-Terphenyl linked donor–π–acceptor dyads: intramolecular charge transfer controlled by electron acceptor group tuning

Dyads were prepared to understand the electronic effects of a meta-terphenyl linker according to the accepting ability change. The charge transfer properties in the ground/excited state are determined by accepting ability and/or steric hindrance.