Push‐pull dibenzodioxins with electron withdrawing and donating groups were prepared in good yields through a short and simple synthesis. Strong green emission above 500 nm occurs in those derivatives where there is maximum charge transfer to the most electron deficit terephthalonitrile ring, from proximal cyclic amino donor groups. Theoretical calculations support experimental findings through evaluation of excited state properties. In molecules with a nitro group, the excited state localizes electron density exclusively onto it and twisted nitro geometry was also found. In effect, electronic charge cannot relocate into the molecular plane, rendering them non‐fluorescent. Also, studies on the fluorescent derivatives show that best emission would occur when the donor moiety contains a saturated cyclic amino ring and the amines are 2°. Overall, our study establishes structure‐property guidelines and limits on dibenzodioxin functionalization towards preparing fluorescent derivatives of the same.

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Push-pull dibenzodioxins and phenazines having ‘anthracene-like’ planar structures and good charge transfer character had been previously synthesised in our laboratory. The dibenzodioxins had earlier proven their anti-proliferative nature against HeLa tumor cell lines. Since phenazines are structural analogues of the former, these molecules were evaluated in course of the current study for their cytotoxic action against HeLa cell lines and they exhibited strong anti-tumor activity. This behavior could be related to their good DNA binding property. The DNA binding modes of molecules 1 – 4 (Fig. 1) were evaluated using various experimental techniques and they interacted with DNA in a non-covalently by both intercalative as well as groove binding mechanisms. Molecule 1 follows predominantly intercalative binding mode whereas molecules 2 and 3 have nearly equal and opposite preferences for both groove binding and intercalative modes. For molecule 4 , groove binding is preferred mode of binding to DNA. A rationale for such differential binding behaviour is provided based on the subtle structural differences in our synthesised dibenzodioxins and phenazines. Elucidation of the mode of a molecule-DNA-binding event is relevant for understanding the mechanism of action of these molecules and will help promote further research into designing better DNA targeting small molecules.

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Chlorins are a class of reduced porphyrins with a very intense longest wavelength Q band (Q y) in the red region, due to their non-planar conformations. This fact is useful in fields like photodynamic therapy and organic photovoltaics, which rely upon the long wavelength absorptivity of the photosensitizing dyes. Here, we have reviewed the synthesis and optical properties of many novel β-meso-annulated chlorins, which possess bathochromic shifts in their optical spectra, compared to their non-fused analogues. In general, we find that these red-shifts are promoted by planarization of the macrocycle caused by β-meso-ring fusion. However, in select examples of ring-fused chlorins bearing an additional non-pyrrolic subunit, in fact we see strong deviation from planar conformation contrary to the general trend. These molecules show Q y bands in the NIR region, but with reduced absorptivity.

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Phenazines bearing electron-donor and electron-acceptor groups with high pH-sensing behavior were synthesized in moderate to good yields. Theoretical calculations on the frontier molecular orbitals and experimental oxidation potential measurements under variable pH values provide evidence for extensive internal charge transfer at high pH value. The well-known strong affinity of the catecholate moiety present in our phenazines is utilized for spectrophotometric detection of Fe3+ ion. Fluorescence-quenching behavior of the prepared phenazines is utilized for detection and distinction of electron-rich and electron-poor aromatics.

A porphyrinoid containing cis‐diol pyrroline subunit and fused nitro‐quinoxaline π‐elongated unit at its peripheral β,β’‐positions was prepared. The UV‐visible spectrum exhibits typical chlorin‐like sharp Qy‐band, but significantly more red‐shifted (687 nm) and more intense than for a normal diol chlorin. The precursor porphyrin exhibited weak Q‐bands slightly above 650 nm. The same porphyrin exhibited a low pH dependent ∼40 nm red‐shift in its UV‐visible spectrum. Analysis of the frontier molecular orbital energies using electrochemical techniques and theoretical analysis of the lowest energy geometry of the porphyrin confirmed the roles of non‐planar conformation and electronic charge redistribution in inducing this spectral feature. In addition, biophysical and computational analysis of DNA‐binding behavior of these porphyrinoids indicated that groove binding induced by Van der Waals contacts was the preferred mode of interaction.