New naphthalene polyimide with unusual molar absorption coefficient and excited state properties: Synthesis, photophysics and electrochemistry

Abstract A high molecular weight 1,4,5,8-naphthalene polyimide (ENPI) by one-step polycondensation mechanism and for comparison its monomeric diimide (ENDI) were synthesized; the photophysical and electrochemical properties were studied in detail for ENPI . Monomer has shown unusual insolubility so that the characterization proven to be difficult, whereas ENPI has shown better solubility. The molecular weight data obtained by GPC for the polymer were M n =8240 and M w =34,000 g mol −1 respectively with a polydispersity of 4.13. The polyimide exhibited outstandingly high molar absorption coefficients as 599,000, 1,021,000, and 972,700 M −1  cm −1 , which is first time reported in literature for the characteristic 0–2, 0–1, and 0–0 electronic transitions, respectively. ENPI showed concentration dependent and red shifted excimer emission in 1,1,2,2-tetrachloroethane (TCE). The polymer has undergone multielectron reductions in CHCl 3 solution below 100 mV s −1 scan rates which merged into two reversible one-electron reduction peaks at higher scan rates. In solid-state, similar scan rate dependent reduction peaks were noticed. The LUMO, HOMO and optical band gap values obtained for ENPI were −3.73, −6.91, and 3.18 eV respectively. ENDI polymer with striking features has great potential as new sensitizer for efficient dye sensitized organic cells.