Photochemical & Photobiological Sciences PAPER Cite this: Photochem. Photobiol. Sci., 2019, 18, 1333 Received 2nd January 2019, Accepted 10th March 2019 DOI: 10.1039/c9pp00003h rsc.li/pps Synthesis and photophysical properties of pyridyl conjugated triazole appended naphthalenediimide derivatives† Girijesh Kumar, * a Ramu Guda, b Ahmad Husain, c Ranjan Patra, a Kirandeep a and Mamatha Kasula b A series of three substituted triazole appended NDI-derivatives, 2,7-bis(3,5-di(pyridin-X-yl)-4H-1,2,4- triazol-4-yl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone (where X = 2, NDI-PyTz-1; 3, NDI-PyTz-2; and 4, NDI-PyTz-3), were designed, synthesized and well characterized using various analytical and spectroscopic techniques. All the three NDI-PyTz derivatives exhibit decent electronic properties as suggested by DFT, cyclic voltammetry and fluorescence studies. In particular, NDI-PyTz-1 demonstrated the generation of a stable anion radical [NDI-PyTz-1] •− . Introduction Recently, the design and construction of electron-rich and electron-deficient (hetero)aromatic moieties containing organic materials have attracted tremendous attention from the scientific community because of their wide range of appli- cations as semiconducting materials, for example, as optical memory devices, photo-optical devices, switching and display devices and so on. 1–7 In this regard, several electron acceptor moieties such as diketopyrrolopyrrole, 8 dicyanovinylene, 9 benzothiadiazole, 10 [1,2,5]-thiadiazolo[3,4-g]quinoxaline, 11 per- ylene diimide, 12–14 isoindigo, 15 and naphthalene diimide (NDI) 16–22 based building blocks have been previously explored. So far, a number of NDI derivatives offering various appended groups, e.g., 4-pyridyl, 4-pyridylmethyl, bis(4-n-butyl- phenyl), bis(4-t-butylphenyl, bis{4-[bis(4-butylphenyl)-amino] phenyl}, thiophene, bithiophene, and thienylene-vinylene-thie- nylene, have been synthesized and their chemistry has been explored significantly. 23 In principle, the NDI unit offers a planar conjugated bicyclic electron rich (10π electrons) aro- matic structure accomplished by displaying strong π–π and van der Waals interactions in the building blocks and thus exhibits better electron transporting properties and ability to self- assemble. Furthermore, the introduction of the pyridyl substi- tuted triazole unit at the N-position of the imide ring not only advances the physical properties in terms of their solubility but also increases their self-assembly process and crystalliza- tion by offering various types of supramolecular interactions. 24–27 In addition, pyridyl substituted triazoles are also very famous for their chelating and/or bridging behavior as well. The electron-deficient nature of the NDI core (accep- tor) and the presence of the electron-rich pyridyl substituted triazole (donor) unit reduce the HOMO–LUMO energy band gap and therefore make them suitable for semiconducting materials. 28 Thus, comprehensive research into the structures of the electron-accepting nature of the NDI core and the possi- bility of the introduction of several interesting electron-rich functionalities either at the imide-N or at the naphthalene ring provides extra advantage to the design and development of new NDI-based semiconducting materials in the near future. So, based on the aforementioned fascinating chemistry of the NDI-based organic compounds, herein, we report the design and syntheses of three novel NDI-derivatives, 2,7-bis (3,5-di(pyridin-X-yl)-4H-1,2,4-triazol-4-yl)benzo[lmn][3,8]phen- anthroline-1,3,6,8(2H,7H)-tetraone (where X = 2, NDI-PyTz-1; 3, NDI-PyTz-2; and 4, NDI-PyTz-3). We have also explored the electrochemical behaviour, DFT calculation and their fluo- rescence properties to corroborate their electronic properties. Experimental Materials and methods The starting materials such as 2-cyanopyridine, 3-cyanopyri- dine, 4-cyanopyridine, hydrazine hydrate, hydrazine sulfate, ethylene glycol, DMF (anhydrous) and 1,4,5,8-naphthalenete- † Electronic supplementary information (ESI) available: Experimental and characterization details, single crystal data collection and bonding parameters, thermal analysis, UV-Vis, powder XRD and electrochemical behavior. CCDC 1537786. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c9pp00003h a Department of Chemistry & Centre for Advanced Studies in Chemistry, Panjab University, Chandigarh–160014, India. E-mail: gkumar@pu.ac.in, girijeshchem@gmail.com b Department of Chemistry, Kakatiya University, Warangal–506009, India c Department of Chemistry, DAV University Jalandhar, Punjab–144012, India This journal is © The Royal Society of Chemistry and Owner Societies 2019 Photochem. Photobiol. Sci. , 2019, 18, 1333–1341 | 1333