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Zinc porphyrins (ZnP) are an important class of small molecule donors that have gained significant attention in the domain of organic photovoltaics. In this work, we investigate and correlate various photophysical and third-order nonlinear optical (NLO) properties of three different zinc porphyrin molecules: a monomer – ZnP1 (ZnP-TEH-DPP) with two diketopyrrolopyrrole (DPP) units bridged to zinc porphyrins, its corresponding porphyrin dimer ZnP2 (ZnP2-DPP) with an additional porphyrin unit at the centre, and another porphyrin dimer ZnP3 (HDDPP-EHTOM) having two zinc porphyrin donors linked with DPP and endcapped with 3-ethylrhodanine. To investigate the excited state dynamics of the systems, a femtosecond transient absorption spectroscopy (fs-TAS) experiment was employed in the visible range by exciting the molecules at 2.53 eV. The estimated lifetime values from the global analysis were in the range of 230–560 fs, 10–27 ps, and 200–350 ps, which is attributed to the internal conversion, vibrational relaxation, and relaxation from the lowest excited singlet state, respectively. Furthermore, the NLO features of ZnP1, ZnP2, and ZnP3 were investigated using a femtosecond Z-scan technique. All the three samples exhibited saturable absorption (SA) at lower intensities and SA followed by reverse saturable absorption (RSA) at higher input intensities. The second hyperpolarizability (γ) from closed aperture Z-scan measurements was estimated to be 5.72 × 10−31, 7.02 × 10−31, and 10.6 × 10−31 esu for ZnP1, ZnP2, and ZnP3, respectively, which were consistent with the theoretically obtained ones using the DFT calculations. Zinc porphyrin dimers (ZnP2 and ZnP3) having extended π-conjugated systems exhibit better NLO properties in comparison to the monomer ZnP1. The observed properties of these samples revealed that these porphyrins can be useful for organic photovoltaic as well as other NLO applications. [ABSTRACT FROM AUTHOR]

A new series of β-functionalized meso-tetraphenylporphyrins bearing 4-methoxyphenyl, 3,5-dimethoxyphenyl and 3,4,5-trimethoxyphenyl groups appended selectively to the single pyrrole unit of the porphyrin macrocycle, H2TPPR2 (where R = p-CH3O-Ph, m-CH3O-Ph and m,p-CH3O-Ph), and their Co(II), Ni(II), Cu(II) and Zn(II) metal complexes were synthesized, characterized and meticulously examined for their adjustable electronic spectral, electrochemical and structural attributes. A gradual bathochromic shift of absorption bands (Δλmax = 5–8 nm) was observed in these porphyrins relative to the unsubstituted parent porphyrin, H2TPP. A progressive cathodic shift in the first ring oxidation potential was observed in the series. Among all free base porphyrins, H2TPP(p-CH3O-Ph)2 showed the maximum red shifted absorption and the largest cathodic shift in the first ring oxidation, unveiling the effective electron donation via the +R effect of methoxy groups placed at the para position of β-phenyl rings. Within this framework, fine-tuning of the HOMO–LUMO gap accompanied by a gradual reduction in energy was observed which followed the trend H2TPP(m,p-CH3O-Ph)2 (2.22 V) > H2TPP(m-CH3O-Ph)2 (2.13 V) > H2TPP(p-CH3O-Ph)2 (2.08 V). Single crystal X-ray analyses of H2TPP(p-CH3O-Ph)2, ZnTPP(m-CH3O-Ph)2 and CuTPP(m-CH3O-Ph)2 unfolded planar, quasi-planar and saddle conformations respectively. Hirshfeld surface and 2D fingerprint plot analysis were also performed to see the significant intermolecular interactions. Further, DFT and TDDFT calculations were performed to gain a deeper understanding of the observed experimental results. [ABSTRACT FROM AUTHOR]

In recent years, lead-containing perovskite quantum dots (PQDs) have sparked a great deal of research in sensing applications as a result of their exceptional optoelectronic characteristics. However, due to their poor stability in ambient air and polar solvents such as water, they are not suitable as probes to detect analytes under aqueous conditions. The present study introduces a rapid and simple fluorescent approach for the sensing of bilirubin (BR) using ultrasonication-assisted synthesis of ethylenediaminetetraacetic acid functionalized CsPbBr3 PQDs (EDTA@CsPbBr3 PQDs) as optical nanoprobes. The as-prepared EDTA@CsPbBr3 PQDs displayed intense green fluorescence under UV light (365 nm) with excellent water stability. The fluorescence emission intensity (at 525 nm) of EDTA@CsPbBr3 PQDs was drastically decreased with the introduction of BR via an inner filter effect mechanism. The developed method for the assay of BR exhibited a broad linear range of concentration (0.05–25 μM) and low limit of detection (15.94 nM) with good selectivity. This study could open a path for the fabrication of water-dispersed PQDs with selective identification of BR, which is essential for sensing applications. [ABSTRACT FROM AUTHOR]

The structural, optoelectronic, and charge-transport properties of linearly fused polycyclic hydrocarbon molecules with heteroatoms (NH, O, S, and Se) in five-membered rings have been investigated using the DFT approach. The hybrid functional B3LYP in combination with the 6–311 + G (d,p) basis set is utilized in the Gaussian 16 W software package for all the calculations. The absorption and emission energies are investigated by using time-dependent density functional theory (TD-DFT) at the same level of theory. To investigate the stability of each molecule concerning its aromaticity, nucleus-independent chemical shift (NICS) values are computed. Electron affinity (EA), hole extraction potential (HEP), ionization potential (IP), and electron extraction potential (EEP) are also reported. The simulated hole (λh) and electron (λe) reorganization energies for the majority of the molecules are lower than the characteristics hole and electron-transporting materials. The reported fused polycyclic compounds may have potential applications in optoelectronic devices. [ABSTRACT FROM AUTHOR]