Energy Transfer in Near-Orthogonally Arranged Chromophores Separated through a Single Bond

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• 作者：Rijo T. Cheriya ; Jimmy Joy ; Andrews P. Alex ; Anil Shaji ; Mahesh Hariharan
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：June 14, 2012
• 年：2012
• 卷：116
• 期：23
• 页码：12489-12498
• 全文大小：556K
• 年卷期：v.116,no.23(June 14, 2012)
• ISSN：1932-7455

文摘

A combined experimental and theoretical study shows a significant barrier (ca. 100 kJ/mol) to rotation through the interchromophoric carbon鈥揷arbon single covalent (1.49 脜) bond between the naphthalenimide and perylenimide units that prevents coplanarization of the two units in the dyad NP, thereby forcing them to act as independent chromophores/redox centers. Upon photoexcitation, highly efficient energy transfer is observed from the naphthalenimide (energy donor) to the perylenimide (energy acceptor) moiety predominantly through Coulombic coupling, completely isolating the orbital overlap (Dexter-type) interaction between the chromophoric units at such short separation by virtue of their orthogonal arrangement. Because F枚rster鈥檚 ideal-dipole approximation ignores the contribution from significant higher-order Coulombic interactions at such short distances between donor and acceptor moieties, the complete coupling was computed from the transition densities, giving an estimate of the energy-transfer rate from the naphthalenimide donor to the perylenimide acceptor of k_ET = 2.2 脳 10¹⁰ s^鈥?, in agreement with observations. Ultrafast excitation energy (ca. 40 ps, 90%) and electron (<0.5 ps, 10%) transfer from the singlet excited state of naphthalenimide to the perylenimide moiety competes with further delayed processes in the conjugate NP. Upon excitation at 345 nm, conjugate NP exhibits near-quantitative energy transfer in conjunction with solvent-polarity-dependent (solvatochromic) perylenimide fluorescence, resulting in a remarkable Stoke鈥檚 shift of ca. 175鈥?40 nm. Favorable photophysical properties such as high fluorescence quantum yield, wide excitation range, ultrafast energy transfer, marginal electron transfer, and large Stoke鈥檚 shift make this conjugate a potential candidate for biological applications.