Firstly, the phototophysical properties of the monomolecular species of TPA-CO2H in dilute 2-MeTHF (1 × 10 -5 M) were studied (Figure ). At 298 K, the steady-state photoluminescence (PL) spectrum is unstructured, with a PL maximum, lPL, of 386 nm, while no afterglow was observed. At 77 K, the steady-state PL spectrum shows emission from two states. The high-energy emission appears at the same energy as the steady-state PL at room temperature and is structured, this associated with fluorescence from a predominantly locally excited (LE) state. The low-energy structured delayed emission (acquired between 1-10 ms after excitation) is assigned to phosphorescence, peaking at lPh of 446 nm. The singlet-triplet energy gap (DEST), determined from the onsets of the 77 K steady-state PL and phosphorescence spectra, is 0.56 eV, which is too large for thermally activated delayed fluorescence to occur. These PL spectra and state energies at 77 K are similar to those recorded in a 1:1 ethanol:methanol glass (Figure ), resulting in a similar DEST of 0.58 eV. As expected, due to the presence of the hydrogen bonding interaction between the solvent and TPA-CO2H, the steadystate PL has a larger phosphorescence component and a longer tPh of 604.5 ms, compared to that in 2-MeTHF (tPh = 517.8 ms) (Figure ); there is, however, no detected RTP. We next explored the photophysical properties of TPA-CO2H in a rigid, nonpolar, and non-H-bonding polymer matrix, Zeonex (Figure ). The behavior of the 1 wt% doped film in Zeonex at RT and 77 K largely mirrors those in 2-MeTHF, with no RTP observed; of note, the fluorescence is slightly red-shifted at lPL of 415 nm. Similarly, there was no RTP detected in 1 wt% doped films of TPA-CO2H in other non-Hbonding matrixes such as 1,3-bis(N-carbazolyl)benzene (mCP), 2,6-bis(3-(carbazol-9yl)phenyl)pyridine (2,6DCzPPy) and naphthalene (Figure ). These results indicate that the structural motion cannot be sufficiently supressed to activate RTP in non-H-bonding matrices.