LAUSR

The coumarin derivatives are documented as exceptional luminophores. However, using them in devices directly has posed challenges due to photodegradation. Herein, the environmentally benign matrix chitosan, with its excellent film‐forming nature, has been taken as a base for fabricating blue emissive composite films doped with 7‐diethylamino‐4‐methyl coumarin (DEAMC). The dopant‐dependent surface morphological, mechanical, thermal, and structural changes of the composite films are revealed by standard characterization techniques. These dopant‐dependent changes are due to the dopant–matrix interaction via H‐bonding between CO and NH2 groups of the dopant and matrix, respectively. The UV‐transparent chitosan matrix converted to excellent UV‐absorbing films upon composite formation with λmax at 375 nm. The calculated direct optical bandgap is found to be in the range of 3.01–2.95 eV, indicating the semiconducting nature of the films. The emission max for the films is at 465 nm, with a bathochromic shift from 432 nm of the pure dopant DEAMC, with the gain in quantum yield from 19.55% to 43.16%. The refractive index of 1.4–2.15 and proper blue emission with Stoke's shift of 60 nm is advantageous for these composite films. The inherently X‐aggregated DEAMC, when doped into polar chitosan, uniquely creates blue emissive, easy processable, low‐cost optical material which could be used in optoelectronic devices.