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Photoresponsive conjugated polymers are a promising target for modern organic electronics. Numerous photoswitchable repeat units have been included covalently within polymeric structures to enable responsive chromic materials, most commonly through side‐chain appendages or through formal conjugation along a π‐conjugated backbone. We recently disclosed a new design whereby the photoswitch elements are cross conjugated to a conjugated polymer main chain. In this case, we found that the extent of photoconversion was dictated in part by competitive main chain light absorption, which could be suppressed by using a photoswitching motif that carried most of the frontier molecular orbital densities. Here, we report the modeling and synthesis of a series of thieno[3,4‐b]thiophene (TT)‐based photochromes with various aromatic flankers imparting varying degrees of steric bulk and π‐conjugation in order to elucidate the balancing act between steric and electronic factors to promote photochromism. These model systems provide a better understanding of the behavior of photochromic units within extended oligomeric and polymeric π‐conjugated materials. [ABSTRACT FROM AUTHOR]

An efficiency of delocalization in strongly conjugated systems remains an important factor crucial for modulation of the optical properties directly correlated with its range. An ortho‐substituted phenylene derivative bearing electron donating/accepting functionality was built‐in a fully unsaturated macrocyclic system with a global delocalization of a diatropic and/or a paratropic current. A precisely located structural modification influence observed behaviour in spectroscopic parameters that are only slightly recognizable in 4n+2 systems but showing a significant influence on the reduced derivatives with a contribution of 4n π‐electrons delocalization path. [ABSTRACT FROM AUTHOR]

A diradical/biradical character of organic derivatives is one of the key aspects of contemporary research focusing on the fundamental studies followed by potential applicability relying on the unique optical, electronic, or magnetic properties assigned to unpaired electrons. A precise involvement of two p‐phenylenes into a cyclophane‐like conjugated, diatropic system creates a flexible molecule with the two different characters of both subunits (benzene and quinone) imprinting into the structure a Kekulé delocalized system. A dynamic of both carbocyclic subunits, and their mutual interaction generates a singlet open‐shell state (J=−1.25 kcal/mol) as documented spectroscopically (NMR and EPR). The extended theoretical analysis has proved a correlation between dihedral angle and the diradicaloid character that shifts from a closed‐shell singlet to an open‐shell state, eventually showing the y0=0.86 for 78 degrees and ΔEST=−0.34 kcal/mol. [ABSTRACT FROM AUTHOR]

A series of novel 2,6‐functionalized azulene molecules Azu1‐3 with varied fluorene substituents at the 1‐ and 3‐positions of azulene as well as at the 5'‐position of 2‐thiophene group were synthesized. Their electronic absorption and emission spectra at neutral and protonated states were examined. It was found that after functionalization with fluorenyl groups, Azu1‐3 exhibited absorption maxima at 445, 451 to 468 nm, respectively. In contrast, their corresponding protonated species showed much redshifted absorption maxima at 560, 582 to 643 nm, respectively, mainly due to the extension of conjugation length and the large dipole moment along the C2v axis of 2,6‐substituted azulene molecules. Azu1‐3 are non‐fluorescent in their neutral forms, but became emissive in their protonated states. Analysis of absorption and emission spectra shows that substitution of the 1‐ or 3‐position of azulene led to decrease in response to trifluoroacetic acid. [ABSTRACT FROM AUTHOR]

This article summarizes a series of lectures I presented in Taiwan as a visiting lecturer sponsored by the Ministry of Science and Technology. [ABSTRACT FROM AUTHOR]

Four cross‐conjugated molecules based on the benzo[1,2‐d:4,5‐d']bisoxazole (BBO) moiety have been synthesized from a common synthon. Theoretical studies indicated that these cruciforms had highly segregated HOMO and LUMO levels enabling semi‐autonomous tuning of the LUMO level from the HOMO through substitution along the 2,6‐axis. The experimental data confirms that the HOMO levels within these systems varied by 0.3 eV, whereas the LUMO levels varied by over 1.6 eV when the electron‐density along the 2,6‐axis was increased. The introduction of relatively electron‐deficient moieties along the 2,6‐axis resulted in a bathochromic shift in the absorption profiles concurrent with the stabilization of the LUMO. These substituents also prolonged the photoluminescent lifetimes owing to improved intramolecular charge transfer states between the 4,8‐ and 2,6‐ axis. The BBO cruciforms were evaluated as donor materials in organic solar cells (OSC)s, but the energy‐level mismatches and poor thin film morphology led to poor performance. These results indicate that benzobisoxazole cruciforms are a promising platform for the development of tunable materials for use in organic semiconductors, but improvements in the optical, electronic and film‐forming properties are needed to enable their use in efficient OSCs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Systematic study on the combination of NIR photosensitizer and drag delivery carrier. • Systematic study on the particle sizes and abilities of NIR-photosensitizers. • High-lipid composition carriers was little altered by lipid-soluble molecules. • NIR-photosensitizer and mitochondria-targeting carrier effectively kills pancreatic cancer. Near-infrared (NIR) photosensitizers have great potential to develop various fields of photochemistry, such as photodynamic therapy (PDT) and photocatalysts. Organelle-targeted PDT using NIR light attracts considerable attention to high-efficiency phototherapy. Although drug delivery system (DDS) carriers are often combined with NIR photosensitizers for effective PDT, the systematic correlations between the cargo and DDS carriers are still unclear. In this study, we develop NIR-photosensitizers from a π-extended porphyrin-type sensitizer (rTPA) that allows us to modify the structure and properties with a one-touch operation for the systematic study. Single-step amidations give five rTPA derivatives readily, facilitating comprehensive information about the properties according to their molecular structure and electric charge of the photosensitizer and DDS carriers prepared using a microfluidic device. One of the combinations, rTPA-NH 2 @MP , demonstrates the highest ability among the derivatives to kill pancreatic cancer cells, which are known to be highly lethal. The present study provides a guideline for inventing effective DDS-based NIR-PDT compounds for future photodrugs. [ABSTRACT FROM AUTHOR]

• The effect of conjugation on pyrrole oligomers is addressed by increasing the length of the π -bridge. • The influence on the length of π – conjugation on band gap, absorption maxima, anti-corrosion studies and NLO activity is studied. • QTAIM and NBO analysis highlights the nature of weak interactions including hydrogen bonding in stabilizing these molecules and substantiates the high stability of monomers. • Lifetime analysis indicates that pentamer has more than 3 ns radiative life time. To investigate the influence of π-conjugation on optical properties, models of Pyrrole oligomers with varying π-bridge lengths, ranging from 1 to 5, were constructed. The π-bridge plays a crucial role in tuning and modulating the optoelectronic characteristics of these molecules. By employing FMO (Frontier Molecular Orbital) analysis, the band gap values were determined. Notably, the pyrrole oligomer with a 1π-bridge exhibited a higher band gap (2.68 eV) compared to the 5π-bridge variant (1.53 eV). Moreover, the calculated hyperpolarizability (β°) values exhibited a substantial increase from 37 esu to 1876 esu as the extent of π-conjugation was augmented. This suggests that enhanced π-conjugation promotes greater nonlinear optical properties. Further analysis revealed that the pyrrole oligomer with 5π-bridges displayed maximal absorption at a longer wavelength, specifically 1024 nm. This information provides valuable insights into the absorption characteristics of these molecules. Additionally, the NBO (Natural Bond Orbital) analysis successfully captured the stable donor-acceptor interactions responsible for the ground state stabilization observed in pyrrole oligomers. On the other hand, the QTAIM (Quantum Theory of Atoms in Molecules) analysis provided detailed information regarding weak interactions, such as hydrogen bonding, which contribute to the stabilization of the modeled monomers. In summary, the creation of Pyrrole oligomer models with varying π-bridge lengths facilitated the evaluation of the impact of π-conjugation on the optical properties. The findings indicate that increasing the π-conjugation leads to a decrease in the band gap, an increase in hyperpolarizability, and absorption at longer wavelengths. Additionally, the stability of the ground state and the nature of weak interactions were elucidated through NBO and QTAIM analyses, respectively. [Display omitted] [ABSTRACT FROM AUTHOR]

Two-photon absorption, a third-order phenomenon of nonlinear optics, has received considerable attention from both academic and industrial communities. Extensive studies on organic two-photon absorbents have led to meaningful correlations between structures and the development of efficient two-photon absorption material based on two-photon properties has been accelerated. This short review article focuses on two major areas, two-photon absorption chromophores and 3D microfabrication employing two-photon photopolymerization techniques: (i) design and control of two-photon absorption performances with respect to their molecular geometry and (ii) achievement of various 3D micro-mechanical and photonic systems fabricated by two-photon stereolithography. [ABSTRACT FROM AUTHOR]

1,2-Bis(9-anthracenyl)ethyne was synthesized and a new crystal polymorph was discovered. The previously reported structure was completely planar with a torsional angle between the two anthracenyl rings of 0.0°, whereas the new polymorph had a torsional angle of 66.6°. The new polymorph also stacks differently between molecules and has greater π–electron overlap. In solution, the spectroscopic characteristics of both polymorphs were identical, but in the solid-state, results of red-shifted spectra for the co-planar polymorph indicate a strikingly simple example of the effect on UV–vis and fluorescence spectra of extending π-conjugation wrapped up in one molecule with two polymorphs. It was also determined that the co-planar polymorph is favored with rapid crystallization, whereas the twisted polymorph prefers slow crystallization. This may indicate that the co-planar polymorph is kinetically favored and the twisted polymorph is thermodynamically favored. [ABSTRACT FROM AUTHOR]

[Display omitted] The accurate description of hydrogen bonds (H-bonds) is one of the primary challenges when describing intermolecular forces. Intramolecular hydrogen bonds (IMHB) are even more challenging because of their ill-defined energy and their interplay with π-systems. In this contribution, we investigate the role of π-resonance in the enhancement of IMHBs. This is accomplished by comparing a number of π-conjugated systems to their saturated planar counterparts using intramolecular symmetry adapted perturbation theory (I-SAPT). The change in the composition of the IMHB energies (electrostatics, exchange, induction, and dispersion) due to π-conjugation is examined in detail. The biggest changes are observed in the induction and electrostatics contributions. However, electrostatics is nearly canceled by its exchange counterpart. The importance of induction term is also observed when plotting rotational potential curves for the different energy components. Once the distance between the H-bond donor and acceptor is frozen, the stabilization of IMHBs mostly occurs through the decrease in the exchange term leading to less repulsion. In any case, all results are consistent with expected trends in the resonance-assisted hydrogen bonds (RAHBs), and corroborate the fragmentation procedures used in this study. The closeness of induction contribution to the whole interaction energy and the existence of a linear correlation between the IMHB energy and the induction component show that the induction term is a good predictor of the intramolecular RAHBs stability trends. [ABSTRACT FROM AUTHOR]

The synthesis, structure, and photophysical properties of novel BODIPY–Fischer alkoxy-, thio-, and aminocarbene dyads are reported. The BODIPY chromophore is directly attached to the carbene ligand by an ethylenic spacer, thus forming donor–bridge–acceptor π-extended systems. The extension of the p-conjugation is decisive in the equilibrium geometries of the dyads and is clearly reflected in the corresponding absorption and emission spectra. Whereas the BODIPY fragment is mainly isolated in aminocarbene complexes, it is fully conjugated in alkoxycarbene derivatives. The former thus exhibit the characteristic photophysical properties of BODIPY units, whereas complete suppression of the BODIPY fluorescence emission is observed in the latter, as a direct consequence of the strong electron-accepting character of the (CO)5M=C moiety. As the π-acceptor character of the metal–carbene group can be modified, the electronic properties of the conjugated BODIPY can be tuned. Density functional calculations have been carried out to gain insight into the photophysical properties. [ABSTRACT FROM AUTHOR]

ABSTRACT New carbo[6]helicene derivatives grafted with π-conjugated cyano-phenyl arms were synthesized in enantiopure forms and their π-conjugation examined by UV-vis spectroscopy. The influence of the π-conjugation on the circular dichroism spectra and molar rotations is discussed based on comparing experimental data with results from quantum-chemical calculations. The results highlight the fact that increasing the spatial extension of the π-system in a helicene molecule is an efficient way of increasing its molar rotation. Chirality 25:455-465, 2013. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Abstract: Bis(tri-n-butylstannyl)acetylene was synthesized and used to create a series of symmetric diarylacetylenes via a one-step Stille coupling protocol with Pd(PPh3)4 as the catalyst. In many cases, the product simply crystallized in good yields from the reaction mixture upon cooling after reflux at 100°C or upon removal of solvent. The diarylacetylenes were studied using UV–vis and fluorescence spectroscopies, which showed that naphthyl- and biphenyl-substituted acetylenes had very high solution-state fluorescence quantum yields. [Copyright &y& Elsevier]

A new tin-functionalized benzo[1,2-b:5,4-b']dithiophene building block was synthesized that can provide access to a series of further extended π-conjugated materials for Organic Field-Effect Transistors (OFETs) via Stille coupling protocol, as exemplified in two cases. The syn-configured benzodithiophene scaffold complements the well-established (anti) benzo[1,2-b:4,5-b′]dithiophene unit that has already been successfully employed in OFET devices. DFT-quantum theoretical calculations on a series of organic semiconductors support the selective modification of the band gap by either changing the HOMO, the LUMO, or both. The suitability of the tin-functionalized synthon to efficiently access a variety of organic semiconductor materials with different properties was also confirmed by the study of their photophysical features. [ABSTRACT FROM AUTHOR]

The present paper describes a nonenzymatic chemiresistor sensor based on an azo-polymer and reduced graphene oxide (rGO) as a resistive platform for superoxide radical detection. The sensorial platform was prepared on layer-by-layer-assembled films of poly(azo-Bismarck Brown Y) and reduced graphene oxide by cyclic voltammetry. The nanocomposite film exhibited interesting synergetic properties based on the redox properties of the azo-polymer combined with the good electronic conductivity and stability of graphene. The electrical conductivity mechanism of the graphene-polymer was analyzed by electrochemical impedance and compared to that of an electrode coated with only polymer. The conductance properties of the interlayer formed by π-π stacking between the conjugated structure of the polymer chains and the structure of the graphene sheet are dependent on the applied potential of the system. The performance of the poly(azo-BBY)/rGO film as a chemiresistor material for the sensing of superoxide anions was evaluated by impedance measurements at the applied potential of +0.30 in PBS (7.4). The charge transfer resistance values change substantially in the presence of superoxide in solution. The effect of superoxide on the resistivity of the device is attributed to changes in the oxidation state of the polymer. The impedance measurements in real time (chrono-impedance) with the poly(azo-BBY)/rGO sensor with different superoxide concentrations revealed good linearity behavior between the real impedance and the superoxide anion concentration (0.12–2.6 ​mmol ​L−1) with a detection limit of 81.0 μmol L−1. Image 1 • The investigation of the charge transfer of a chemiresistor material in the presence of different concentrations of superoxide radical. • The resistance values of the material are very sensitive to variations in the superoxide concentration. • The chemiresistor sensor for selective monitoring of superoxide was effective and with possible application in biological systems. [ABSTRACT FROM AUTHOR]

Discrete π‐conjugated zinc porphyrin nanotubes are investigated as molecular analogues of carbon nanotubes. These porphyrin nanotubes have a diameter of 2.4 nm (Zn–Zn distance) and lengths of up to 3.6 nm, measured to the van der Waals surfaces of the outer β‐pyrrole hydrogen atoms, or 4.5 nm measured to the para hydrogen atoms of the aryl groups. We explore three different strategies for synthesizing these nanotubes. The first two strategies use a template to achieve direct or sequential stave‐joining, respectively, and proceed via linear oligomers that pre‐define the length of the nanotube. These strategies are applied to synthesize porphyrin nanotubes containing 12‐ or 18‐porphyrin subunits, with ethynylene (C2) or butadiynylene (C4) links between the 6‐porphyrin nanorings. The third strategy involves the covalent stacking of pre‐formed 6‐porphyrin nanorings to form a 12‐porphyrin nanotube, without using a template to guide this coupling reaction. The nanotubes show strongly red‐shifted absorption spectra and low fluorescence quantum yields, indicating structural rigidity and extensive π‐conjugation. [ABSTRACT FROM AUTHOR]