Unprecedented intense fluorescent emission was observed for a variety of flavin compounds bearing a perpendicular cyclic imide moiety at the C7 position of an isoalloxazine platform. A series of alloxan‐substituted flavins was prepared selectively by reduction of the corresponding N‐aryl‐2‐nitro‐5‐alkoxyanilines with zinc dust and subsequent reaction with alloxan monohydrate in the presence of boric acid. Analogues bearing oxazolidine‐2,4‐dione functionality were obtained on methylation of the alloxan‐substituted flavins with methyl iodide and subsequent rearrangement in the presence of an inorganic base. The flavin compounds exhibit intense white‐green fluorescent emission in the solution state under UV excitation at 298 K, with emission efficiencies Φ298 K greater than 0.55 in CH3CN, which are higher than the values for all reported flavin compounds under similar conditions. The highest Φ298 K value of 0.70 was obtained in CH3CN for isoalloxazine bearing C7‐alloxan and N10‐2,6‐diisopropylphenyl groups. The temperature dependence of the emission intensities indicates that the pronounced emission properties at 298 K are attributable to the highly heat resistant properties towards emission decay with increasing temperature. Mechanistic studies, including X‐ray diffraction analysis, revealed that the good emission properties and high heat resistance of the alloxan‐substituted flavins are due to a synergetic effect of the associative nature of the C7‐alloxan unit and the repulsive nature of the perpendicular bulky substituents at the C7 and N10 positions.