Electron, Hole, Singlet, and Triplet Energy Transfer in Photoexcited Porphyrin-Naphthalenediimide Dyads

Abstract

The excited-state dynamics of two molecular dyads, consisting of zinc (1) and free-base (2) porphyrin connected via a peptide linker to a core-substituted naphthalenediimide (NDI) have been investigated using optical spectroscopy. These dyads exhibit rich photophysics because of the large number of electronic excited states below 3 eV. In the case of 1 in apolar solvents, excitation energy transfer from the vibrationally hot singlet excited porphyrin to the NDI takes place with a 500 fs time constant. Electronic energy ends up in the NDI-localized triplet state, which decays to the ground state on a microsecond timescale. In polar solvents, ground-state recovery is faster by 5 orders of magnitude because of the occurrence of charge separation followed by recombination. On the other hand, excitation energy transfer in 2 takes place in the opposite direction, namely from the NDI to the porphyrin, which then undergoes intersystem crossing to the triplet state, followed by triplet energy transfer back to the NDI. Therefore, four distinct local electronic excited states are consecutively populated after excitation of the NDI unit of 2, with the energy shuttling between the two ends of the dyad.

Triphenylamine disubstituted naphthalene diimide: elucidation of excited states involved in TADF and application in near-infrared organic light emitting diodes

“…Although to this point never used in OLED applications, NDIs have found a home in many donoracceptor based systems, (most especially in porphyrin-NDI based dyads). [27][28][29] In these dyads, they form photoinduced intramolecular charge-separated states -a molecular requirement for the fabrication of many TADF OLED materials. The design of TADF materials that cater towards specific OLED device manufacture requires the critical arrangement of the local triplet ( 3 LE) and charge-transfer states ( 1 CT and 3 CT) to promote the spin-vibronic coupling that underpins rISC and TADF.…”

A Triphenylamine–Naphthalenediimide–Fullerene Triad: Synthesis, Photoinduced Charge Separation and Solution‐Processable Bulk Heterojunction Solar Cells

“…[11][12][13][14] Naphthalenediimide (NDI) is one such unit and hasastrongly electron-deficient planar structure, is able to extend p-conjugation, and is known to exhibit n-type semiconducting properties. [15,16] NDI derivativesh ave attracted considerable interest as electron acceptors in photoinduced chargeseparation [17][18][19][20][21] and in the fabrication of organic electronic devices. [22,23] Incorporation of electron-withdrawing subunits at the core of NDIs has been shown to significantly improve the efficiency of BHJ devicesi f blendedw ith the conventional donorp olymer P3HT.…”

Long-lived triplet charge-separated state in naphthalenediimide based donor–acceptor systems

“…[1][2][3][4][5][6][7] Their high oxidative power and the good stability of their radical anions make NDIs popular electron accepting units in multichromophoric systems. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] In principle, they can also act as chromophores due to their strong p-p* transition around 375 nm. In contrast to their bigger brother, the perylenediimide, 27 unsubstituted NDIs have a low uorescence quantum yield and a very short S 1 state lifetime arising from a fast intersystem crossing (ISC).…”