Figure shows results at a 10 wt% doping concentration. The emission in mCP is blueshifted at lPL of 496 nm, compared to that of the doped PMMA film. The ΦPL of the doped film in mCP is 57.4% under N2, which decreased to 53.5% in air. The τp = 24.9 ns and the average τd = 5.3 µs [τ1=1.4 µs (46.8%), τ2=7.7 µs (53.2%)]. In both PMMA and mCP matrices at 10% doping the delayed emission is thermally activated (Figure ). However, extracting detailed information from such highly doped matrices is dangerous because of spurious phenomena, including homo energy-transfer and inner filter effects (selfabsorption). To minimize spurious concentration effects, low-concentration (down to 1 wt%) films were fabricated, relevant spectra being shown in Figure . In these films both the high frequency emission originating from the bent structure, and the low-frequency emission from the orthogonal structure, are present, suggesting that both conformers are present in all films. The high frequency emission decays much more rapidly (Figure ), again confirming that it originates from the bent conformer. Upon increasing concentration, the high frequency emission progressively weakens and disappears for doping concentrations above 3 wt%. Two phenomena may exist to explain this observation, both related to the large transition dipole moment (large oscillator strength) of the S0→S1 transition in the bent geometry: (1) self-absorption; and (2) energy transfer from the bent to the orthogonal structure. Both phenomena are expected to become more efficient upon increasing the concentration of the emitter in the host matrix.