The structural studies of 2-[(4-tert-butylphenyl)-5–(4-biphenyl)]-1, 3, 4- oxadiazole (PBD) incorporated γ ray irradiated chitosan films for optoelectronic applications

Abstract

Herein, versatile biopolymer chitosan films doped with 2-[(4-‑tert-butylphenyl)-5–(4-biphenyl)]-1, 3, 4- oxadiazole (PBD) a known OLED material were prepared by intercalation method. These films witnessed crosslinking which in turn exhibited exciting properties due to gamma irradiation with varied dosages. The radical mediated crosslinking of NH2 group with t‑butyl group was envisaged by the increased crystallinity of the films. The XPS analysis showed the formation of the bond between dopant and polymer backbone. The changes in binding energies of unirradiated and irradiated CHPBD films for N1s from 399.08 eV (1° amine) to 400.7 eV (2°amine), supported reaction of NH2 group with t‑butyl group of PBD in crosslinking of dopant and polymer matrix with the formation of CN linkage. In PXRD, peaks centered around 21.24° for pristine chitosan film, but for the unirradiated CHPBD, it was shifted to the lower angle16.09° to form amorphous film. However, for the irradiated CHPBD shifting to the higher angle 22.9°, 23.08°, 27.23° suggesting that dopant had chemically interacted with the polymer matrix. The Young's modulus, tensile strength indicated supportive properties. An interesting change in UV absorption behavior was observed for the unirradiated CHPBD exhibiting λmax at 290 nm with a hypsochromic shift with respected to dopant (λmax,309 nm). This indicated weak head-to-head alignment of dyes in an unirradiated matrix; whereas irradiation brought about changes through chemical crosslinking in the architecture of films with a redshift to 309 nm. Hyperchromism was also the effect of irradiation on films. The unirradiated films exhibited emission maxima around 369 nm whereas irradiated films showed 412 nm. Hence, a simple method was developed for the preparation of blue emissive biopolymeric materials.