Structure and Photoinduced Electron Transfer Dynamics of a Series of Hydrogen-Bonded Supramolecular Complexes Composed of Electron Donors and a Saddle-Distorted Diprotonated Porphyrin

Abstract

The excited-state photodynamics of intrasupramolecular photoinduced electron transfer was investigated in a series of hydrogen-bonded supramolecular complexes composed of diprotonated 2,3,5,7,8,10,12,13,15,17,18,20-dodecaphenylporphyrin (H(4)DPP(2+)) and electron donors bearing a carboxylate group. The formation of supramolecular complexes was examined by spectroscopic measurements. The binding constants obtained by spectroscopic titration indicate the strong binding (10(8)-10(10) M(-2)) even in a polar and coordinating solvent, benzonitrile (PhCN). The crystal structure of the supramolecular assembly using ferrocenecarboxylate (FcCOO(-)) was determined to reveal a new structural motif involving two-point and single-point hydrogen bonding among saddle-distorted H(4)DPP(2+) dication and two FcCOO(-) anions. Femtosecond laser flash photolysis was applied to investigate the photodynamics in the hydrogen-bonded supramolecular complexes. Rate constants obtained were evaluated in light of the Marcus theory of electron transfer, allowing us to determine the reorganization energy and the electronic coupling matrix constant of photoinduced electron transfer and back electron transfer to be 0.68 eV and 43 cm(-1), respectively. The distance dependence of electron transfer was also examined by using a series of ferrocenecarboxylate derivatives connected by linear phenylene linkers, and the distance dependence of the rate constant of electron transfer (k(ET)) was determined to be k(ET) = k(0) exp(-beta r), in which beta = 0.64 A(-1).

Thermodynamics and Photodynamics of a Monoprotonated Porphyrin Directly Stabilized by Hydrogen Bonding with Polar Protic Solvents

“…[28] Protonation equilibrium of H 2 Ph as been widely investigated for severald ecades because of the crucialinfluences on redox and photophysicalproperties of H 2 P. [28][29][30][31][32][33][34][35] In general, H 2 Pe xhibits ap lanar conformation due to the 18p-conjugated heteroaromatic macrocyclic structure including four pyrrolem oieties,w hich are capable of accepting two protons at two available lone pairs of pyrrole nitrogen atoms. [46][47][48][49][50][51][52][53][54][55][56] In spite of the fact that the detection of H 3 P + is indispensable for thermodynamic elucidation of an acid-base equilibrium of H 2 Pa sshown in Scheme 1, the detection and characterization have been seldom reporteds ofar. Protonation of H 2 Pu sually proceeds in one step withouta ny detectable monoprotonated porphyrin (H 3 P + )a s an intermediate in sharp contrast to dibasicd iamines, such as ethylenediamine, which showc lear two-step protonation involving as table monoprotonated species (K 1 @ K 2 in Scheme 1a).…”

Quantum-Сhemical Insight into the Reactivity of 5-Bromo-10,20-diaryl-porphyrins towards Nucleophiles

“…While the extension of basis set with the polarizing and diffuse functions may increase the quantitative accuracy of the obtained data, the 6-31G* basis set provides compensated compromise between the accuracy and time-consuming characteristics of the calculation. The B3LYP/6-31G* level of theory is widely applied for the calculation of the characteristics of porphyrins and their metal complexes, such as structural parameters, [26][27][28][29][30] electronic coupling, [26] energy profiles, [27,30] electron transfer and charge separation, [31,32] molecular orbitals localization, [28,29,[31][32][33] spectral properties. [29,30] We attempted to evaluate the reactivity of bromoporphyrins 2a-g towards nucleophiles using the value of a skew angle between the nitrogen atom lone pair and the porphyrin plane.…”

Hydrogen-bonding dynamics of photoexcited coumarin 138 and 339 in protic methanol solution: Time-dependent density functional theory study

“…This intermolecular interaction can assemble multiple molecules into a cluster, which is formed in the ground state and influence a series of photophysical processes, such as internal conversion (IC), photoinduced proton transfer (PPT), and photoinduced electron transfer (PET) [8][9][10][11][12][13][14]. The numerous researchers and engineers are making efforts to understand the hydrogen bonding dynamics with theoretical and experimental methods, exploring the applications in photoelectronics, such as fluorescence probe, optical sensor and light emitting devices [6,[15][16][17][18][19][20][21][22].…”