Benzothiadiazole Units Research Articles

Molecular origin of photostability for fluorene-based donor–acceptor type photovoltaic polymers

Quantitative analyses of photodegradation for three fluorene-based photovoltaic polymers, poly[2,7-(9,9-dioctyl-fluorene)-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (APFO3), polyfluorene (PFO), and poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT), were conducted to understand the molecular origin of photostability for polymers. The Fourier transform infrared spectra of the polymer thin films varied with irradiating white light at 100 mW cm−2 irrespective of their molecular architectures. The absorption peaks corresponding to alkyl side chains in the fluorene unit decreased, whereas those for polymers that did not comprise carbonyl groups increased. This spectral variation indicates that alkyl side chains in the fluorene unit decompose when the molecular structure of fluorene changes to that of fluorenone. The reaction rate constant of the formation of C=O bonds for APFO3 was 1.64 × 10−5 s−1, lower than those for PFO (7.59 × 10−5 s−1) and F8BT (2.64 × 10−5 s−1), under light irradiation at 30 °C. The photostability of the polymers was improved by designing a donor–acceptor type molecular architecture incorporating photostable electron-deficient benzothiadiazole units with photo-unstable fluorene units.

Growth of New Linear Phenylene-Oxazole Oligomers with a Central Benzothiadiazole Fragment from Solutions of Crystals

For the first time, the results on the solubility and growth of new oligomers with a single conjugated core from solutions of organic crystals are reported. The new oligomers consist of benzothiadiazole, phenylene, and oxazole units and have various terminal substituents. Using DSC and TGA methods, melting parameters are found and thermal stability upon heating is studied.

Porphyrin sensitizers involving a fluorine-substituted benzothiadiazole as auxiliary acceptor and thiophene as π bridge for use in dye-sensitized solar cells (DSSCs)

Three ‘donor–acceptor–π bridge–acceptor’ (D–A–π–A) type zinc porphyrin sensitizers TH-0F, TH-1F and TH-2F with a benzothiadiazole (BTD) unit bearing no fluorine, one fluorine and two fluorine atoms, respectively, as the auxiliary acceptor and thiophene as the π bridge were designed and synthesized for use in dye-sensitized solar cells (DSSCs). The influence of fluorine atom and thiophene unit on the photophysical and photochemical properties of the sensitizers was investigated. It was shown that the photon to current conversion efficiencies (PCE) of three sensitizer-based devices increased in the order of TH-2F > TH-1F > TH-0F, with the highest PCE of 6.98% achieved for the TH-2F-based device. To further understand the molecular structure of the TH series of dyes, a density functional (DFT) calculation was performed. The result suggests that the strong electron-withdrawing ability of the fluorine atom, along with the intramolecular interaction between the auxiliary acceptor and thiophene, optimized the electronic configuration, thereby facilitating the intramolecular charge transfer efficiency and ultimately improving the performance of the corresponding device.

The Effect of Ring Expansion in Thienobenzo[b]indacenodithiophene Polymers for Organic Field-Effect Transistors.

A fused donor, thienobenzo[b]indacenodithiophene (TBIDT), was designed and synthesized using a novel acid-promoted cascade ring closure strategy, and then copolymerized with a benzothiadiazole (BT) monomer. The backbone of TBIDT is an expansion of the well-known indacenodithiophene (IDT) unit and was expected to enhance the charge carrier mobility by improving backbone planarity and facilitating short contacts between polymer chains. However, the optimized field-effect transistors demonstrated an average saturation hole mobility of 0.9 cm2 V-1 s-1, lower than the performance of IDT-BT (∼1.5 cm2 V-1 s-1). Mobilities extracted from time-resolved microwave conductivity measurements were consistent with the trend in hole mobilities in organic field-effect transistor devices. Scanning tunneling microscopy measurements and computational modeling illustrated that TBIDT-BT exhibits a less ordered microstructure in comparison to IDT-BT. This reveals that a regular side-chain packing density, independent of conformational isomers, is critical to avoid local free volume due to irregular packing, which can host trapping impurities. DFT calculations indicated that TBIDT-BT, despite containing a larger, planar unit, showed less stabilization of planar backbone geometries in comparison to IDT-BT. This is due to the reduced electrostatic stabilizing interactions between the peripheral thiophene of the fused core and the BT unit, resulting in a reduction of the barrier to rotation around the single bond. These insights provide a greater understanding of the general structure-property relationships required for semiconducting polymer repeat units to ensure optimal backbone planarization, as illustrated with IDT-type units, guiding the design of novel semiconducting polymers with extended fused backbones for high-performance field-effect transistors.

Synthesis and optical properties of polymers with bithiophene condensed with disilacyclohexadiene rings and benzothiadiazole

New types of polymers composed of bithiophene condensed with disilacyclohexadiene rings and benzothiadiazole were prepared by the platinum-catalyzed dehydrogenative bissilylation. UV–Vis absorption and fluorescence properties of these polymers have been investigated. The fluorescence spectra of these polymers showed only the bands ascribed to the benzothiadiazole units even when the bithiophene units were irradiated. For these polymers, photoenergy transfer occurs from donor to acceptor. DFT calculations were performed to understand the photophysical properties of the polymers.

Synthesis of conjugated polymers with directly coupled 2-butyloctyloxybenzodithiophene and benzothiadazole units for application as active layers in organic solar cells

One of the fastest growing areas in polymer science is the photovoltaic organic devices, which conjugated polymers are an important part of, since they constitute the core of bulk heterojunction active layer. In this work two benzodithiophene based polymers containing fluorinated and non-fluorinated benzothiadiazole units were successfully synthesized. It was observed that chain growth depends upon the nature of the electron deficient monomer, being fluorinated monomer able to produce higher chain size and distribution. Low band gap was obtained (1.71 and 1.72 eV for fluorinated and non-fluorinated polymers, respectively) as well as values of −3.78 and −3.66 eV for LUMO orbitals energy were estimated. The synthesized polymers presented degradation temperatures above 280 °C, which makes them able to be processed through roll-to-roll deposition techniques. Charge carriers mobilities are 4.6 × 10−6 and 1.0 × 10−5 cm2 V−1.s−1 for non-fluorinated and fluorinated polymers, respectively: this last higher charge carrier mobility was attributed to the interaction between the fluorine atoms and the adjacent aromatic sulfur, which according to other authors promotes planarity and consequently, it favors the charge carriers mobility. AFM images showed a higher roughness correlated with phase separation for fluorinated polymer; conduction paths with dimensions less than 25 nm were detected which is positive for future improvement of solar devices.

Graphene oxide as a surfactant in the nanostructuring of a conduction polymer: Effect on the electronic structure, chain orientation, and charge transfer dynamics

Abstract The search for new structures, new synthetic paths, and new processing technologies is crucial for the future of electronic devices. In this context, this work reports a novel and simple miniemulsion-way to achieve nanostructured polymers in aqueous solution using graphene oxide (GO) as a surfactant for electronic applications. The materials were prepared using the Pickering emulsion concepts, where the graphene oxide colloidal dispersion was sonicated along with toluene solutions of the organic semiconductive polymer poly[2,7-(9,9-bis(2-ethylhexyl)-dibenzosilole)-alt-4,7-bis(thiophen-2-yl) benzo-2,1,3-thiadiazole] (PSiF-DBT). We have investigated various PSiF: GO ratios as well as the effect of the pH on the thin film preparation, by the liquid-liquid interfacial method. Scanning and transmission electron microscopy (SEM and TEM) and atomic force microscopy (AFM) images showed that the morphology of the films is strongly dependent on both the amount of the polymer and the pH. Infrared spectroscopy suggests the anchoring of Si atoms from the PSiF-DBT in some oxygenated groups of graphene oxide, explaining better the angle-resolved near-edge X-ray absorption fine structure (NEXAFS) results, that indicate an upright-standing molecular orientation for the thiophene units and a lying-down orientation for the benzothiadiazole units. UV–Vis molecular absorption and resonant Auger spectroscopies indicated that the charge transfer is faster the higher are the ratio of PSiF: GO in the film.

Quantum theory of atoms in molecules for photovoltaics

Electronic properties of benzothiadiazole (BTD) unit containing dyes adsorbed on TiO2 nano-particles have been estimated using Quantum Theory of Atoms in Molecules (QTAIM). We found that short circuit photocurrent density Jsc and open circuit photovoltage Voc of the studied DSSCs are well related to the electronic properties of dyes, namely charges of BTD atomic basins of nitrogens, summary isodensity surface area and summary volume of hydrogen basins. Analysis of deviations of predicted and observed photovoltaic properties allowed to reveal device fabrication details influencing positively and negatively on device efficiency. Found relationships have been used for design of new promising dyes and recommendation of the better fabrication details of DSSCs with significantly higher photovoltaic properties as compared to the studied and published. For newly designed metal-free BTD-unit containing dyes, Jsc is expected to reach 20.7–25.8 mA/cm2, Voc – 0.858–1.029 V and power conversion efficiency η – 10.6–16.3%.

An A−D−Aʹ−Dʹ strategy enables perylenediimide-based polymer dyes exhibiting enhanced electron transport characteristics

In this work, we develop two new A−D−Aʹ−Dʹ type polymer dyes, namely PPDIDTBT and PPDIDTBT-2F, containing perylenediimide (PDI), thiophene, and benzothiadiazole units. Both polymer dyes have high thermal stability and broad absorption throughout the UV–vis region. More importantly, the introduction of the second electron-withdrawing units, benzothiadiazoles, endows both polymer dyes with low-lying LUMO energy levels of −3.85 eV for PPDIDTBT and −3.88 eV for PPDIDTBT-2F. The charge transport properties of the two polymer dyes were examined by fabricating organic field-effect transistors (OFETs) with top-gate/bottom-contact configuration. Both polymer dyes exhibit enhanced electron transport characteristics with the highest electron mobility of 0.070 cm2 V−1 s−1, which is among the highest values for PDI-based polymer semiconductors reported to date. Our results highlight that the A−D−Aʹ−Dʹ strategy is a useful approach in tuning orbital energetic and charge transport properties of polymer dyes for developing high-performance OFETs.

Solar cells sensitized with porphyrin dyes with a carbazole donor: The effects of an auxiliary benzothiadiazole acceptor and bulky substituents on the donor

Three porphyrin sensitizers XW54–XW56 containing a carbazole donor have been designed and synthesized by introducing a benzothiadiazole (BTD) unit as the auxiliary electron acceptor to extend the absorption spectra and/or bulky dihexyloxyphenyl groups into the carbazole unit to suppress dye aggregation and improve the photovoltage (Voc). The BTD unit incorporated in XW54 obviously broadens and red-shifts the absorption threshold to ca. 700 nm, as compared with that of 650 nm observed for XW1. Thus, XW54 exhibits a much broader monochromatic photon-to-electron conversion efficiency (IPCE) spectrum with an extremely red-shifted onset wavelength of 780 nm, resulting in a photocurrent density (Jsc) of 11.60 mA cm−2, higher than that of XW1. Unfortunately, the Voc value was decreased owing to the more severe dye aggregation caused by the large conjugation framework induced by the presence of the BTD unit. As a result, XW54 shows an efficiency of 6.26%, slightly higher than that of 6.11% obtained for XW1. On the other hand, with the bulky dihexyloxyphenyl donor groups introduced to XW55, a highest Voc of 860 mV was achieved, which can be ascribed to the efficient prevention of charge recombination and suppression of dye aggregation. Thus, XW55-based cells exhibit an improved efficiency of 6.60%. On the basis of XW54 and XW55, two bulky dihexyloxyphenyl groups and a BTD unit were simultaneously introduced to XW56, affording a highest efficiency of 7.03%, with the Jsc and Voc values of 12.5 mA cm−2 and 785 mV, respectively. These results compose a novel approach for developing efficient dye-sensitized solar cells (DSSCs) by simultaneously introducing bulky dihexyloxyphenyl groups and a benzothiadiazole unit, which may synergistically broaden the absorption spectra and suppress the dye aggregation, resulting in improved photocurrent and photovoltage.

Enhancing the JSC of P3HT-Based OSCs via a Thiophene-Fused Aromatic Heterocycle as a "π-Bridge" for A-π-D-π-A-Type Acceptors.

Poly(3-hexylthiophene) (P3HT)-based organic solar cells (OSCs) have been extensively studied due to unique advantages of P3HT such as roll-to-roll and large-area printing fabrication, but a poor short-circuit current density greatly limits the enhancement of power conversion efficiency (PCE). Herein, via the thiophene-fused aromatic heterocycle as a "π-bridge", two "A-π-D-π-A"-type acceptors have been designed and synthesized for P3HT-based OSCs. The aromaticity of the fused thiophene ring has effectively stabilized the quinoid population, thus strengthening the intramolecular charge transfer and further improving the current density. Owing to the weaker electron-withdrawing ability of the thiophene-fused benzotriazole unit in JC2 than the thiophene-fused benzothiadiazole unit in JC1, a blue-shifted absorption occurs for JC2 to show a better complementarity with P3HT to improve the light-harvesting efficiency and current density of the derived OSCs, and an uplifted lowest unoccupied molecular orbital energy level is also achieved for JC2 to obtain higher voltages. Thus, the P3HT:JC2-based device exhibits a PCE of 6.24% with a high JSC of 13.96 mA cm-2 and a VOC of 0.71 V, significantly exceeding those of the P3HT:JC1 device with a PCE of 2.80%, a JSC of 10.66 mA cm-2, and a VOC of 0.48 V. This indicates that the fusion of a thiophene ring onto a benzotriazole unit is an effective strategy to balance the VOC and JSC of P3HT-based OSCs to achieve excellent photovoltaic performances.

Effective design of A-D-A small molecules for high performance organic solar cells via F atom substitution and thiophene bridge

Three novel small molecules with acceptor-donor-acceptor (A-D-A) configuration, SBDT1, SBDT2 and SBDT3, where 4,8-bis(octyloxy)benzo[1,2-b:4,5-b′]dithiophene (BDT) as the electron-donating core connecting to thiophene-substituted benzothiadiazole (BT) as electron-withdrawing are reported. The effects of fluorine atoms on the photophysical properties by introducing different fluorine atoms into the benzothiadiazole unit were investigated. These SBDTs exhibit good thermal stability, excellent panchromatic absorption in solution and film. SBDT2 and SBDT3 with fluorine-substituted BT possess a relatively deeper the highest occupied molecular orbital (HOMO). These A-D-A type molecules were treated as donor and PC71BM as acceptor in bulk heterojunction (BHJ) small-molecule organic solar cells (SMOSCs). Among them, device based on SBDT2 gave the best device performance with a PCE of 5.06% with Jsc of 10.56 mA/cm2, Voc of 0.85 V, fill factor (FF) of 56.4%. These studies indicate that proper incorporation of fluorine atoms is an effective way to increase the efficiency of organic solar cells.

Poly(arylenevinylene)s through Ring-Opening Metathesis Polymerization of an Unsymmetrical Donor-Acceptor Cyclophane.

Reported are well-defined donor-acceptor alternating copolymers prepared using ring-opening metathesis polymerization (ROMP). Unsymmetrical cyclophanedienes comprising electron-donating (4-methoxy-1-(2-ethylhexyl)oxy)benzene (MEH) and electron-accepting benzothiadiazole (BT) rings were synthesized from the corresponding [3.3]dithiaparacyclophanes. ROMP of the strained unsymmetrical and "electronically-ambiguous" cyclophanedienes proceeded in a controlled manner in the presence of either Hoveyda-Grubbs II or Grubbs II initiator in wake of both steric and electronic encumbrance. The resulting polymers, comprising alternating BT and MEH-PPV units, are achieved in molecular weights exceeding 20k with Đ values ranging from 1.1-1.4. The living nature of the polymerization is verified through the formation of rod-coil and rod-rod block copolymers. Our strategy to develop previously unrealized polymers from functional building blocks featuring a locked-in D-A unit is significant in a field striving to achieve well-defined and sequence-specific materials.

Development of fullerene free acceptors molecules for organic solar cells: A step way forward toward efficient organic solar cells

Continuous strides are being made to explore non-fullerene acceptors for organic solar cells. Here, optoelectronic properties of four new acceptor-donor-acceptor (A-D-A) type non-fullerene acceptor molecules are evaluated for their potential use in organic solar cells. The designed molecules contain indacenodithiophene (IDT) donor core connected with various acceptor groups through benzothiadiazole (BT) bridge unit. The designed molecules differ from each other in end-capped acceptor groups. The end-capped acceptors are 2-methylene-3-oxo-2,3-dihydroinden-1-ylidene) malononitrile (M1), 2,5,6-difluoro-2-methylene-3-oxo-2,3-dihydroinden-1-ylidene) malononitrile (M2), 2-methylene-2-H-indene-1,3-dione (M3), and 2,5-methylene-6-oxo-5,6-dihydrocyclopenta-c-thiphen-4-ylidene-malononitrile (M4). The optoelectronic properties are evaluated in comparison with the recently reported R which is structurally similar to the designed molecules. The reference compound R contains indacenodithiophene (IDT) donor core unit with 3-ethyl-d-ethylidene-2-thioxothiazolidin-4-one end capped acceptor group. The A-D-A acceptor molecules evaluated here exhibit proper frontier molecular orbital diagram to facilitate the charge mobility. M2, containing 2-(5,6-difluoro-2-methylene-3-oxo-2,3-dihydroinden-1-ylidene) malononitrile end-capped acceptor group, exhibits maximum absorption at 805 nm which is attributed to extended conjugation with the BT unit. Results of transition density matrix (TDM) show clear effect of end caped acceptor group on electro-hole exciton. Small coupling of electron and hole in M4 illustrates easy dissociation of exciton as compared with other molecules. Among all, M4 shows the highest hole transfer rate as revealed from low hole reorganization energy (λh). The open circuit voltage (Voc) of reference R is 1.96 V with donor polymer PTB7-Th while the designed molecule M3 exhibits the Voc of 2.02 V. Hence, the designed fullerene free acceptor molecules are suitable for transparent organic solar cells.

(Invited) Benzothiadiazole-Based Dye Photosensitizers for Water Splitting Using Dye-Encapsulated Carbon Nanotubes

A donor-acceptor-donor (D-A-D) dye consisting of ferrocene units (donors) and a benzothiadiazole unit (acceptor) was synthesized to use the photosensitizer for hydrogen evolution reaction (HER) from water within semiconducting single-walled carbon nanotube (s-SWCNT). The dye was easily encapsulated into s-SWCNT by a solution method to form dye-encapsulated s-SWCNTs (dye@SWCNTs). Subsequently, physical modification of dye@SWCNTs by a fullerodendron gave dye@SWCNT/fullerodendron nanohybrids having dye/s-SWCNT/C60 coaxial heterojunction. Interestingly, dye@SWCNT/fullerodendron nanohybrids act as the photosensitizer for HER in the presence of sacrificial donor, electron relay, and co-catalyst due to the mobile carrier generation upon photoexcitation of the dye molecules.

Efficient solar cells based on cosensitizing porphyrin dyes containing a wrapped donor, a wrapped π-framework and a substituted benzothiadiazole unit

Three new porphyrin dyes XW45 − XW47 have been synthesized employing a dialkoxy-wrapped phenothiazine donor, a tetraalkoxy-wrapped porphyrin π-framework, a benzothiadiazole (BTD)-based auxiliary acceptor, and an anchoring benzoic acid group. On the basis of our previously reported dye XW36 , XW45 was synthesized by introducing a BTD unit to broaden the absorption spectrum, further introducing a hexyl-substituent into the BTD unit afforded XW46 , and an additional fluorine atom was introduced to the carboxyphenyl acceptor to afford XW47 . As expected, the BTD unit obviously broadens and red-shifts the absorption threshold of XW45 − XW47 to ca . 750 nm. Dye-sensitized solar cells (DSSCs) were fabricated based on a cobalt electrolyte using chenodeoxycholic acid (CDCA) as the coadsorbent. Under full sun illumination, XW45 exhibits an efficiency of 9.73%, which is slightly lower than that of 10.19% obtained for the reference dye SM315 . By contrast, XW46 and XW47 show higher efficiencies than SM315 owing to the improved anti-aggregation ability associated with the hexyl group on the BTD unit and better ICT effect induced by the fluorine atom on the carboxyphenyl unit. Thus, XW47 exhibits the highest efficiency of 10.41% among the porphyrin dyes. Furthermore, PT-C6 was used as the cosensitizer to improve the light harvesting ability and efficiencies of the cells due to its broad absorption within 350–560 nm. Thus, high efficiencies of 10.32%, 11.38% and 10.90% were achieved for the cosensitized solar cells based on XW45 – XW47 , respectively, owing to the obviously enhanced photocurrent density ( J SC). In addition, under 30% full sun illumination, XW46 + PT-C6 exhibits a high efficiency of 13.08%. These results give an effective method for building high performance DSSCs through the cosensitization of porphyrin dyes containing a wrapped donor, a wrapped porphyrin framework and a properly substituted auxiliary benzothiadiazole unit.

Low-bandgap polymers with quinoid unit as π bridge for high-performance solar cells

Abstract To construct efficient low band gap polymers, increasing the Quinone structure of the polymer backbone could be one desirable strategy. In this work, two D –Q–A–Q polymers P1 and P2 were designed and synthesized with thiophenopyrrole diketone (TPD) and benzothiadiazole (BT) unit as the core and ester linked thieno[3,4-b]thiophene (TT) segment as π-bridging, and the main focus is to make a comparative analysis of different cores in the influence of the optical, electrochemical, photochemical and morphological properties. Compared with the reported PBDTTEH–TBTTHD−i, P1 exhibited the decreased HOMO energy level of −5.38 eV and lower bandgap of 1.48 eV. Furthermore, when replaced with BT core, P2 showed a red-shifted absorption profile of polymer but with up-shifted HOMO energy level. When fabricated the photovoltaic devices in conventional structure, just as expected, the introduction of ester substituent made an obvious increase of VOC from 0.63 to 0.74 V for P1. Besides, due to the deep HOMO energy level, higher hole mobility and excellent phase separation with PC71BM, a superior photovoltaic performance (PCE = 7.13%) was obtained with a short-circuit current density (JSC) of 14.9 mA/cm2, significantly higher than that of P2 (PCE = 2.23%). Generally, this study highlights that the strategy of inserting quinoid moieties into D –A polymers could be optional in LBG-polymers design and presents the importance and comparison of potentially competent core groups.

Molecular design of benzothiadiazole-based dyes for working with carbon nanotube photocatalysts

A donor–acceptor–donor (D–A–D) dye consisting of ferrocene units (donors) and a benzothiadiazole unit (acceptor) was synthesized to use the photosensitizer for hydrogen evolution reaction (HER) from water within semiconducting single-walled carbon nanotube (s-SWCNT). The dye was easily encapsulated into s-SWCNT by a solution method to form dye-encapsulated s-SWCNTs (dye@SWCNTs). Subsequently, physical modification of dye@SWCNTs by a fullerodendron gave dye@SWCNT/fullerodendron nanohybrids having dye/s-SWCNT/C60 coaxial heterojunction. Interestingly, dye@SWCNT/fullerodendron nanohybrids act as the photosensitizer for HER in the presence of sacrificial donor, electron relay, and co-catalyst due to the mobile carrier generation upon photoexcitation of the dye molecules.

Thiadiazolo-Azaacenes.

This work reports the synthesis and characterization of bis- and tetrakis(thiadiazolo)-appended di- and tetraazaacenes, displaying up to seven catenated benzene/pyrazine rings. The targets are obtained by condensation of benzo-bis(thiadiazole)-4,5-dione with aromatic di- and tetraamines. The condensation products-up to a heptacene-like species-are stable but can be insoluble. Soluble derivatives are readily processible, but do not show enhanced electron affinities, as the two or four attached benzothiadiazole units are effectively resonance-separated from the acene body, maximizing the number of Clar-sextets.

Spirobifluorene based small molecules as an alternative to traditional fullerene acceptors for organic solar cells

Four new three-dimensional (3D) acceptor-acceptor-donor (A-A-D) type of small molecule acceptors (M1, M2, M3 and M4) were designed for better optoelectronic properties in organic solar cells. These molecules contain spirobifluorene as a 3D core unit, flanked with 2,1,3- benzothiadiazole (BT) units linked with the end-capped acceptor groups 2-(4-oxo-4,5-dihydrocyclopenta-b-thiophene-6-ylidene)malononitrile (M1), 2-(3-oxo-2,3-dihydro-1H-indene-1-indene-1-ylidene)malononitrile (M2), 2-(5,6-difluoro-3-oxo-2,3-dihydroindene-1-ylidene)malononitrile (M3) and 2-(5,6-dimethyl-3-oxo-2,3-dihydroindene-1-ylidene)malononitrile (M4). The optoelectronic properties of M1-M4 were compared with the well-known reference molecule R, which has the same central BT-spirobifluorene-BT structure as M1-M4 but is end-capped with the 2-(2-dicyanomethylene)-3-ethyl-4-oxo-thiazolidin-5-ylidenemethyl group. Among these molecules, M3 has the most appropriate frontier molecular orbital diagram for optoelectronic properties as deduced from MPW1PW91 calculations and also shows the maximum absorption peak at longest wavelength (569 nm) by TD-MPW1PW91 calculations with a polarizable continuum model for chloroform solution. These properties are due to the strong electron-withdrawing end-capped acceptor group which causes a red shift in the absorption spectrum. Computed reorganization energies indicate that the electron mobilities for M1-M4 are higher compared to that of reference R.