A process for producing an oxidation reaction product of a raw material aromatic compound comprising a benzene, naphthalene or thiophene aromatic ring having at least one substituent selected from the group consisting of -OR 100, -NR 200 2, and -AR 100 which is covalently bound to the benzene, naphthalene or thiophene ring, R 100 is a hydrogen atom or an arbitrary substituent, and when a plurality of R 100 s are present, they may be identical to or different from each other, R 200 s are each a hydrogen atom or an arbitrary substituent, and they may be identical to or different from each other, and AR 100 is an aryl group, and when a plurality of AR 100 s are present, they may be identical to or different from each other, which process comprises reacting the raw material aromatic compound with an oxidizing agent which is oxygen as an elementary substance, wherein the process further uses an electron donor-acceptor linked molecule, and a Brønsted acid selected from hydrogen halides, sulfuric acid, nitric acid, sulfonic acid, carboxylic acids and phosphoric acid and anions thereof, and the process comprises the steps of: generating an electron-transfer state of the electron donor-acceptor linked molecule by photoexcitation; reacting the electron donor-acceptor linked molecule in the electron-transfer state, the oxidizing agent, the raw material aromatic compound, and the Brønsted acid or anion thereof thereby generating an oxidation reaction product, wherein; the oxidation reaction product comprises a substitution product obtained by substitution of at least one hydrogen atom on an aromatic ring of the raw material aromatic compound with an atom or atomic group of the Brønsted acid anion, and the electron donor-acceptor linked molecule is at least one selected from the group consisting of: nitrogen-containing aromatic cation derivatives represented by the following formulae (A-1) to (A-8); 9-substituted acridinium ions represented by the following formula (A-9); quinolinium ion derivatives represented by the following formula; stereoisomers and tautomers thereof; and salts thereof: where in the formulae (A-1) to (A-8) and (A-9), R is a hydrogen atom or an arbitrary substituent, Ar is the electron donor group, and the number of Ars may be one or more, and when a plurality of Ars are present, they may be identical to or different from each other, a nitrogen-containing aromatic ring that forms a nitrogen-containing aromatic cation may or may not contain at least one arbitrary substituent other than R and Ar, and in the formula, R 1 is a hydrogen atom or an arbitrary substituent, Ar 1 to Ar 3 are each a hydrogen atom or the electron donor group and may be identical to or different from each other, and at least one of Ar 1 to Ar 3 is the electron donor group. generating an electron-transfer state of the electron donor-acceptor linked molecule by photoexcitation; reacting the electron donor-acceptor linked molecule in the electron-transfer state, the oxidizing agent, the raw material aromatic compound, and the Brønsted acid or anion thereof thereby generating an oxidation reaction product, wherein; the oxidation reaction product comprises a substitution product obtained by substitution of at least one hydrogen atom on an aromatic ring of the raw material aromatic compound with an atom or atomic group of the Brønsted acid anion, and the electron donor-acceptor linked molecule is at least one selected from the group consisting of: nitrogen-containing aromatic cation derivatives represented by the following formulae (A-1) to (A-8); 9-substituted acridinium ions represented by the following formula (A-9); quinolinium ion derivatives represented by the following formula; stereoisomers and tautomers thereof; and salts thereof: where in the formulae (A-1) to (A-8) and (A-9), R is a hydrogen atom or an arbitrary substituent, Ar is the electron donor group, and the number of Ars may be one or more, and when a plurality of Ars are present, they may be identical to or different from each other, a nitrogen-containing aromatic ring that forms a nitrogen-containing aromatic cation may or may not contain at least one arbitrary substituent other than R and Ar, and in the formula, R 1 is a hydrogen atom or an arbitrary substituent, Ar 1 to Ar 3 are each a hydrogen atom or the electron donor group and may be identical to or different from each other, and at least one of Ar 1 to Ar 3 is the electron donor group.