Symmetry-breaking charge separation (SB-CS) has recently evolved as an emerging concept offering its potential in the latest generation of organic photovoltaics. But there are several concerns that need to be addressed to reach the state-of-the-art in SB-CS chemistry, for instance, the desirable molecular geometry, interchromophoric distance and extent of electronic coupling. To shed light on those features, herein, ortho-functionalized perylene monoimide (PMI) constituted regioisomeric dimer and trimer derivatives with varied molecular twisting and electronic conjugation have been synthesized. In steady-state photophysical studies, all the dimers and trimer derivatives exhibit larger bathochromic shift in emission spectra and significant reduction of fluorescence quantum yield in polar DMF. Among the series of multichromophores, ortho- and self-coupled dimers display strikingly different optical feature of SB-CS with very fast charge separation rate (= 80.2 ps) upon photoexcitation in DMF, which is unveiled by femtosecond transient absorption (fs-TA) studies. SB-CS for two dimers is well-supported by the formation of and band in fs-TA spectra. However, other multichromophores did not exhibit a clear charge separation, they undergo relaxation to the ground state. Additionally, the charge separation dynamics of two aforesaid PMI derivatives is devoid of kinetically favorable excimer or triplet formation. The evidence of a profound charge transfer phenomenon in ortho-dimer is characterized by density functional theory (DFT) calculations on excited state electronic structures. The excitonic communications in the excited state electronic arrangements unravel the key role of dihedral twisting in SB-CS. The thermodynamic feasibility of CS (ΔGCS) and activation barrier () of the derivatives in DMF are established from the Rehm-Weller equation and Marcus’s theory, respectively. This work deciphers an in-depth study of the effect of mutual orientation of PMIs and regioisomerism in determining the sustainable guideline of SB-CS.

This article is Open Access

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