Cross Conjugated Organometallic Polymers Exhibiting Ultrafast Excitation Energy Channeling: Drastic Effect of the Connectivity

Abstract

A polymer composed of 2,6‐diethynylanthraquinone diimine (AQI) and trans‐bis(tributylphosphine)platinum(II), [Pt], flanked by one tetraphenylpalladium(II)porphyrin (TPPPd) and one para‐nitrobenzene (C6H4NO2) is prepared (P1: M n = 57000, M w = 124500, Đ = 2.18, DP = 52.5) and is studied by time‐resolved emission spectroscopy and fs transient absorption spectroscopy (fs‐TAS). A model polymer (AQI(C6H4NO2)2‐[Pt]) n is used for comparison (P2: M n = 88200, M w = 188700, Đ = 2.14, DP = 111). Taking advantage of the dynamics of the excited states of [Pt] and TPPPd and those obtained for P1 and P2, it is shown that the excitation energy absorbed by the central polymer chain, (AQI‐[Pt]) n , channels this energy very efficiently, to the pendent TPPPd with a rate of energy transfer, k ET(S1), larger than 2.3 × 1010 s−1 for an energy transfer 1(AQI‐[Pt])* → TPPPd for P1 at 298 K based on the decrease of the fluorescence lifetime of the (AQI‐[Pt]) n chain in P1 compared to P2. This rate is more accurately estimated by fs‐TAS and is found to be 1.8 × 1011 s−1. This rate is ultrafast and is due to a large contribution of the Dexter mechanism across the imine bridge (CN).