REEs are typically seen in fluorescence spectroscopy under low temperature and viscous solvent conditions where solvent relaxation times are forced to be much longer than fluorescence timescales (𝜏 F ≪ 𝜏 R ), and varied solvent interactions become more accentuated. It is possible that for larger, more conjugated chromophores such as those featuring highly mismatched reactivity and absorbance, these REEs are more readily observed at low viscosities and at room temperature with an increased 𝜏 R and a reduced 𝜏 F . To investigate if these microenvironments are indeed wavelength-selective under similar experimental conditions as those achieved during action plot experiments, both wavelength-dependent steady-state and picosecond (ps) time-resolved fluorescence spectroscopy were utilised for our model molecule, trans-PyChal. Figure displays the results from these experiments, with an excitation wavelength dependence in both the emission wavelength and fluorescence emission lifetimes of trans-PyChal dissolved in acetonitrile. Full details of these experiments are providing in Supporting Information Section S8. Figure shows that the wavelength of maximum fluorescence emission is constant for shorter excitation wavelengths, then becomes increasingly longer at excitation wavelengths along the red-edge of the absorbance tail. A similar trend with the fluorescence lifetime measurements is observed in Figure , showing that two dominant decay components, likely to be fluorescence driven by environmental interactions, each have a similar excitation wavelength dependence on their lifetimes which are rather short-lived (100's of ps). Evaluation of trans-PyChal steady-state fluorescence in other solvents can be found in Supporting Information Section S8, showing wavelengthdependent emissions that are also consistent with the REE, with no observable REE seen in cyclohexane (an orientational polarizability very close to zero), and very large REEs seen for water/PEG (a much higher orientational polarizability of 0.32 observed for water). Further evidence of these selective microenvironments can be seen in the wavelength-dependent time-resolved fluorescence decay profiles (Figure and). When using shorter excitation wavelengths close to the absorption maximum of trans-PyChal, the decay profile can be closely approximated with a mono-exponential fit (Figure ). However, excitation wavelengths at the absorption tail of trans-PyChal result in a decay profile that only matches a higher order exponential fit (Figure ). Moreover, a broader lifetimes distribution is observed for decays collected at the emission tail (Supporting Information Figure ), suggesting that the relaxational component is indeed at a similar timescale to the fluorescence lifetime (𝜏 F ≈ 𝜏 R ). These results suggest that despite being at room temperature in a relatively low viscosity solvent, the trans-PyChal molecule still experiences a distribution of microenvironments, allowing for selective excitation based upon the excitation wavelength utilised. Additionally, the selective excitation leads to increased excitedstate lifetimes of the trans-PyChal molecule at longer wavelengths. In the previous section, we concluded that there must exist a wavelengthdependent quantum yield for the photocycloaddition reaction that is not present in the photoisomerisation reaction. With the distinction of the photocycloaddition reaction being bimolecular in nature and thus dependent on both concentration and lifetime, the excitation wavelength dependence on excited-state lifetimes found in Figure and the excitation wavelength dependence on reactivity found in Figure appear less coincidental. It is this very same connection of wavelength-dependent excitedstate lifetimes, that we therefore propose are responsible for the enhanced quantum yield at longer excitation wavelengths for the [2+2]-photocycloaddition of trans-PyChal.