Small Structural Changes, Large Photophysical Consequences: Fluorescence and Room-Temperature Phosphorescence in Indole-Based Luminophores

The photophysical properties of indole derivatives were investigated with emphasis on their ability to exhibit room-temperature phosphorescence (RTP) and fluorescence. A Jablonski diagram provides the framework to introduce absorption, fluorescence, and phosphorescence as fundamental excited-state processes. N-phenyl-1H-indole-5-carboxamide (Ind-CA) was identified as a compound displaying efficient RTP when immobilized in poly(vinyl alcohol) films. Comprehensive characterization, including absorption spectra, fluorescence anisotropy, phosphorescence emission, and lifetime distributions, demonstrated that immobilization of Ind-CA in the polymer matrix facilitates long-lived triplet emission. Extended studies on isomeric indole carboxamides revealed unique structure-property correlations, thus emphasizing the critical role of positional isomerism in modulating excited-state dynamics, intersystem crossing efficiency, and the manifestation of RTP in indole-based luminophores.