縮環系𝝅共役分子の輻射および無輻射遷移速度

Abstract

Herein, we have studied radiative and nonradiative transition rates (k[r] and k[nr]) of singlet excitons in fused-ring 𝝅-conjugated polymer films by spectroscopic measurements. More specifically, we employed three different conjugated polymers (PTQ1, PNTz4T, PTNT2T) with different sizes of fused-ring 𝝅-conjugation system. In order to evaluate radiative and nonradiative transition rates, we measured fluorescence lifetime [τf] by time-correlated single-photon-counting method and fluorescence quantum yield Φ[f] by absolute photoluminescence quantum yield method. As a result, we found that both [τf] and Φ[f] increased with increasing fused-ring 𝝅-conjugation system in polymer main chains, resulting in smaller k[r] and k[nr]. For radiative transition rates k[r], it can be quantitatively analyzed by Stricker–Berg equation with molar absorption coefficient for each polymer, suggesting that k[r] is mainly governed by the molar absorption coefficient. For nonradiative transition rates k[nr], it can be analyzed by Englman–Jortner equation with reorganization energy λ and vibronic coupling parameter C. For reorganization energy λ, it decreased for larger fused-ring𝝅-conjugation system in polymer main chains, suggesting that rigid fused-rings can suppress λ effectively owing to small structural change and hence can reduce k[nr]. For vibronic coupling parameter 𝘊, it also decreased for larger fused-ring 𝝅-conjugation system in polymer main chains. This is due to smaller C in larger fused-ring 𝝅-conjugation system due to smaller overlap between HOMO and LUMO in the main chain. We therefore conclude that fused-ring 𝝅-conjugation system would be beneficial for designing highly emissive conjugated polymers with well suppressed nonradiative transitions.