Figure 4.
(a) Initial value of the PL anisotropy following excitation with a short (100 fs) light pulse for c-P6·T6 (red), c-P6x·T6 (blue), and l-P6·T6 (green). Dashed lines serve as a guide to the eye. Anisotropy values have been calculated using the PL intensity polarized parallel and orthogonal to the excitation pulse, averaged over the first 5 ps following excitation, during which these intensities do not vary (see Supporting Information). (b) Schematic diagram illustrating the splitting of the k = ±1 level leading to the observed trend in PL anisotropy for l-P6·T6. For the highly symmetric c-P6·T6, Herzberg–Teller effects activate transitions from the k = 0 state to the ground state via vibrational levels (not shown), while for l-P6·T6 with broken π-conjugation such transition may become directly Franck–Condon allowed.